2. Breeding and cultivation of sweet sorghum

2.1. Breeding Shennong no. 2 with high grain yield and high juice sugar content
2.2. Accumulation of dry matter and sugar and formation of yield in sweet sorghum
2.3. Inheritance of sugar content in sorghum stalk
2.4. Research on alcohol production of stalk for several sweet sorghum varieties
2.5. Sweet sorghum production by multiple cropping with early maturing crops
2.6. The effect of different cultivation techniques on sweet sorghum

2.1. Breeding Shennong no. 2 with high grain yield and high juice sugar content

Sorghum belongs to C4 crop with high photosynthetic efficiency and high productivity. It is one of the many types of cultivated sorghum and is characterized by high sugar content in juice of stem. The sugar is composed mainly of saccharose (70-80 %), fructose and glucose, similar to sugar beet. The sugar can be easily fermented to produce ethanol which can be used as a fuel for vehicles. So far sweet sorghum has become a very famous energy plant in the world. For example, in the U.S. many sweet sorghum varieties such as Rio, Wray and Keller have been bred to produce ethanol, in the European Community sweet sorghum as a promising energy crop is being studied now. All sweet sorghum varieties from foreign countries have large plant height but low grain yield. Because of the large population in China, sweet sorghum bred must have both high grain yield and high sugar content in juice of stem in order to develop energy crop without competition of field with food crops. However, the competition between grain and stem exists. Germplasm resource of sorghum shows that sorghum is an old crop and has different productivities among varieties. The new sweet sorghum varieties with high biomass which have high photosynthetic efficiency and can fully use the period of duration will be bred by means of studies on germplasm resource, collection of parents and gene recombination. Famous sorghum breeder of the American F.R. Miller has noticed that sweet sorghum with high energy will be bred by recreating process of inheritance.

We has bred a sweet sorghum hybrid, Shennog No.2, based on the above theory. And the research result will be reported in this paper.

2.1.1 The diversity of sweet sorghum

The economic characters of 58 varieties were compared in Table 2.1.

From Table 2.1 that the period of duration of sweet sorghum is longer, the days to 50 % anthesis over three months. The number of leaves is 2-4 more than that of grain sorghum. The plant height is above 3 metres, but the panicle is very small, with grain weight per head less than 50 g, 1000 kernel weight lower than 20 g. However, the sugar content in juice of stem reaches 16° BX or even more.

Analysis of variation coefficient showed that the diversities of 1000 kernel weight and plant height were maximum in the investigated 7 characters. This indicated that different kernel weights could be got from 11g to 38g and that variation of plant heights from 1.45m to 4.3m could also be found. Coefficient of variation of leaf number was small, which indicated numbers that leaf similar each other. Obviously, the characters such as early maturity, big head of more than 100g and high sugar content of more than 22° BX can not be found among the 58 germplasm resources. Therefore it is necessary to collect germplasm of sweet sorghum more widely in order to meet the requirement of breeding.

Table 2.1. Investigation and analysis of diversity in the main economic caracters for 58 sweet sorghum varieties

Characters	Average Standard (s)	Coefficient (C.V.)	Range of deviation of variation (x)	variation
Days to 50% anthesis	91.3	15.42	16.09	79-106
Number of leaves	21.1	1.78	8.4	17-27
Plan height (m)	3.1	0.897	28.9	1.45-4.3
Diameter of stem (cm)	1.98	0.44	22.2	1.55-2.8
Grain weight per head (g)	43.88	5.396	17.2	16-81.2
1000 kernel weight (g)	18.09	7.55	29.8	11-38
Sugar content in stem juice at maturity ('BX)	16.61	2.82	16.9	9-21

2.1.2 Heterosis of sweet sorghum

29 hybrids were combined with ATx 623 as a female parent and 29 sweet sorghum varieties as male parents for the research on heterosis in some traits such as period of duration, plant height, kernel weight and grain weight per head.

The value of average heterosis in Fl for the period of duration was around 0.91%, which indicated that the period of duration of Fl was in the middle of both parents and that this character was controlled by additive effect of gene. The period of duration of ATx 623 was shorter, with 70-75 days to 50% anthesis, although that of male parent was longer. The average value of heterobeltiosis of 29 combinations was -5.24%. However, some combinations had got high values of average heterosis, for example, the heterosis value of ATx 623 x Roma reached 16.4%.

Fig. 2.1 Distribution of heterosis in days to 50% anthesis of the hybrids compared with their parents

Heterosis of plant height of sweet sorghum was apparently high and the values of average heterosis and heterobeltiosis reached 57.92% and 13.52% respectively. This indicated that plant height was controlled by dominant effect of gene.

Plant height of ATx 623 was small, only 1.15m. If high stalked male parent was used, Fl would be high, ever higher than the taller parent, for example in the combination, ATx 623 x Roma, height of male parent Roma was 2.17m, but Fl was 3.5m.

Heterosis of 1000 kernel weight and grain weight per head is also apparently high, their average heterosis reached 23.1% and 50% respectively. This indicated that grain weight per head was mainly affected by the heterosis of kernel number per head besides the heterosis of 1000 kernel weight.

The study on heterosis of sweet sorghum showed that the hybrids with favorable characters such as high plant, big kernel, large head and resistance to lodging could be bred by means of correct selection of parents. The hybrid ATx 623 x Roma reached the breeding aim mentioned above.

Fig. 2.2. Distribution of heterosis of the hybrids compared with their parents in plant height (Length was calculated from the difference between the hybrid and the mean of the parents)

2.1.3 Study on productivity of ATx 623 x Roma

Combination, ATx 623 x Roma named Shennong No.2 was bred by Sweet Sorghum Breeding Group of Shenyang Agricultural University in 1984, and was examined by a scientist group in Liaoning Province, China in 1985. Shennong No.2 has many favorable characters, such as plant height 3.5m, grain weight per head above 75g, strong stem resistant to lodging, juice rate of stem 65%, sugar content ° BX 16, 1000 kernel weight 32g. The grain is also high quality, for example the contents of protein, lysine and tannin are 10.39%, 0.25% and 0.42 respectively and all these have reached the standard for grain utilization. The results of yield testing experiment showed that Shennong No.2 had high productivity. Its fresh stem yield was 51412.5 kg/ha and grain yield was 5040 kg/ha. Compared with sweet sorghum variety Wray, its yield of stem was 10.2% higher, the yield of grain was 250% higher, and compared with Rio the yields of stem and grain were 21.6% and 116% more respectively. Moreover, the maturity of Shennong No.2 was sooner than that of Rio and Wray.

(1) Heterosis of Shennong No.2

Heterosis of Shennong No.2 was found for the accumulation of dry matter. Fig. 2.3 showed that Shennong No.2 surpassed its both parents in dry matter production from elongation to maturity. Finally, the dry matter per plant of the hybrid reached 365g which was 228% and 192% of its female and male parents respectively.

Figure

Table 2.2 Comparison of productivity within sorghum varieties

Varieties		Biomass kg/ha	Increase (%)
SHENNONG NO. 2		24637.50	-
SWEET* 623AXRTX430		15829.95	55.6
SORGHUM ATLASA X RT X		22449.90	9.7
430		20479.95	20.3
	624A X 78CS5946	13849.95	77.8
	623AXSC0599-11E	21729.90	13.3
	623A X RIO	12789.90	92.6
	RIO
GRAIN** WRAY		16415.40	50.0
SORGHUM C42Y		16216.50	51.9
	SHENNON0447	16518.00	49.1
	Shenza 3	19423.50	26.8
	Tieza 6	18517.50	33.0
	191	18964.50	29.9

* Data from F.R. Miller, R.A. Credand, 1980, 35th Annual Corn and Sorghum Research Conference. **Data from Ma Hongtu, 1986, Studies on productivity of different sorghum genotype, Lioaning Agricultural Science 1.

The strong heterosis of Shennong No.2 resulted in a yield increase of the population. The dry matter of the hybrid reached 12318.75 kg/ha, whereas those of female parent ATx 623 and male parent Roma were 5467.5kg/ha and 6412.5kg/ha respectively. The average heterosis of the hybrid was 110%.

Table 2.2 demonstrated the result of comparison between the hybrid and sweet sorghum varieties from the U.S. and grain sorghum.

The productivity of Shennong No.2 was very high even in the condition of it compared with corn and rice. The biomass of the hybrid was equivalent to 10348.5 kg/ha of corn grain as calculated with the economic coefficient of 0.42 and was equivalent to 12319.5 kg/ha of rice grain as calculated with the ratio of grain to straw of 1: 1.

(2) Photosynthesis of Shennong No.2

LAI, NAR and CGR of Shennong No.2 and its parents were tested in order to learn the heterosis of photosynthetic efficiency of the hybrid through sampling every 10 days from elongation to maturity.

Table 2.3 Comparison of photosynthetic efficiency between Shennong No.2 and its parents

Genotype	LAI	NAR	CGR	Growing
		(elongation to maturity)
ATx 623 x Roma	3.97	5.80	14.50	130
ATx 623	2, 32	5.85	8.85	105
Roma	2.45	6.32	10.48	110

The Figures in Table 2.3 were the results measured under the planting density of 67500 plants/ha, and they showed that the LAI of the hybrid was highest and its NAR was also considerably high.

Shennong No.2 did not show strong heterosis in NAR, but it had more green leaves by maturity. These leaves could keep photosynthesis continually if the temperature was appropriate before harvesting. Thus the hybrid could better use the sun light and growing season and produce more dry matter through photosynthesis. The dry matter could be stored in the stem in the form of sugar.

In short, the high productivity of Shennong No.2 was resulted from its great ability of producing higher LAI, NAR and CGR, in addition to the more green leaves before harvesting.

Fig. 2.4 Comparison of NAR between Shennong No.2 and its parents at different growing stages

(3) Alcohol productivity of Shennong No.2

The alcohol yield from grain and stem of the hybrid was higher than that of other sweet sorghum varieties.

Table 2.4. Comparison of fresh stem, juice rate, sugar content, grain yield and fermented alcohol production among different sweet sorghum varieties

Factors	Date of harvest (month .day)	Varieties					Mean
		Keller	Wray	623A x Rio	623A x Roma	Rio
Fresh stem (kg/ha)	9.18	43215	44505	33750	49875	40658	42401
	9.28	46448	46650	35130	51413	42278	44384
	10.7	49448	49845	42518	52103	47400	48263
Juice rate	9.18	0.44	0.59	0.55	0.55	0.54	0.534
	9.28	0.64	0.70	0.60	0.68	0.64	0.652
	10.7	0.622	0.654	0.619	0.653	0.59	0.628
Sugar degree (°BX)	9.18	17	15	13	16	17.2	15.64
	9.28	17.8	15.8	15.3	16	17.4	16.46
	10.7	19.51	18.51	16.7	16.1	17.5	17.68
Grain yield (kg/ha)	9.28	1642.5	1440	4477.5	5040	2325	2985
	10.7	2077.5	1826.3	4545	5022	3375	3369.3
Alcohol yield from grain (L/ha)	9.28	547.5	480	1417.5	1680	775.5	-
Alcohol yield from stem (L/ha)	9.28	2344.95	2176.95	1241.25	2330.7	2100	-
Total alcohol yield (L/ha)	9.28	2892.45	2656.95	2658.75	4010.7	2875.5	-

Table 2.5. Sugar content and fermented alcohol yield of 6 sweet sorghum varieties at different harvesting dates

Varieties	Sugar degree (°BX)		Fructose (%)		Glucose (%)		Saccharose (%)		Total sugar content of stem (%)		AIcohol degree
	9.18	9.28	9.18	9.28	9.18	9.28	9.18	9.28	9.18	9.28	9.18	9.28
Roma	15.6	17.8	1.50	0.90	2.35	1.45	6.651	0.00	4.16	7.14	6.4	7.0
Keller	17.0	17.8	0.50	0.50	1.30	0.90	8.001	0.60	3.30	7 .62	7.2	7.1
Wray	15.0	15.8	0.45	0.80	0.75	1.45	7.25	9.15	4.01	8.00	5.9	6.0
623A xRio	13.0	15.3	0.95	0.85	1.45	1.30	5.60	8.35	3.00	6.67	4.5	5.3
623A xRoma	16.0	16.0	1.45	1.30	2.30	2.05	6.85	8.00	3.58	7.75	6.7	6.0
Rio	17.2	17.4	0.70	0.60	1.30	1.10	7.701	0.50	3.83	7.77	6.9	7.0

Table 2.4 and Table 2.5 showed that the sugar degree in stem harvested on Sept. 28 was 5.2% higher than that on Sept. 18, and the sugar degree on Oct. 7 was 7.4% higher than that on Sept. 28 . Juice rate was highest on Sept. 28 and saccharose content in stem increased greatly at that time. Suitable date for harvest should be determined according to fresh stem yield, juice rate, sugar degree and grain yield. The data in our experiment showed that the date of harvest on Sept. 28 was very suitable for the stem, but several varieties with late maturity such as Keller, Wray and Rio should be harvested on Oct. 7, because their grain yields increased greatly during the period from Sept. 28 to Oct. 7.

Significant differences in yields of fresh stem and grain between varieties were found through statistical analysis. The fresh stem yields of Shennong No.2, Wray, Keller and Rio were similar, and significantly higher than that of ATx 623 x Rio. The grain yield of Shennong No.2 was the highest among the 5 varieties.

The juice yield per hectare of sweet sorghum could be calculated according to the yield of fresh stem and juice rate. Alcohol production from stem could be calculated according to alcohol degree fermented from juice of stem. Table 2.4 showed that alcohol production from stem for Keller, Wray, Rio and Shennong No.2 was similar. In China not only stem but also grain of sweet sorghum was harvested to produce alcohol. The grain yield of Shennong No.2 reached 5022 kg/ha, which was two times as much as that of Rio, three times as much as that of Keller or Wray. Thus, total alcohol yield of Shennong No.2 from stem and grain reached 4010.25 L/ha, which was 40-50% higher than those of other varieties such as Rio, Wray and Keller.

2.2. Accumulation of dry matter and sugar and formation of yield in sweet sorghum

2.2.1 Introduction

Sweet sorghum is a rising crop for energy and being taken seriously due to its merits of substituting fossil fuel with ethanol extracted from it. This paper presents some results on the study of the accumulation of dry matter and sugar and the formation of yield in sweet sorghum. And by comparing sweet sorghum with grain sorghum, we try to indicate the features of the accumulation and distribution of dry matter and the yield formation theoretically, so that a basis can be provided for the cultivation and breeding of sweet sorghum.

2.2.2 Materials and methods

The field experiments were made with two varieties of sweet sorghum, Shennong No.2 and Rio, and two varieties of grain sorghum, Jinza 4 and Shennong 447, in Shenyang and Tiding in 1978-1988. A randomized block design in 3 replications was carried out. The area of plot was 252 square meters (10mx25.2m). The plant density of sweet sorghum was 61500-78000 plants per hectare and that of grain sorghum was 93750-119445 plants per hectare. 10-15 plants were sampled at intervals of 15 days during the development of plants, and then the dry matter weights of leaf, sheath, stalk and panicle were measured. The saccharinity of various internodes was measured with a handy saccharometer beginning at half a month before heading at intervals of 10 days. The fresh weights of stalk and leaf and the grain yield were measured at the harvest.

2.2.3 Results and analyses

a) Models of dry matter accumulation

The accumulations of dry matter of sweet sorghum and grain sorghum plants were similar, which were of S curve and could be described by using a Logistic equation of Y=K/1+ aexp (-bt). K is environmental capacity standing for the biomass of a ripe plant, a is a constant relating to the special variety, b is relative growth rate. Through the statistical analysis the dry matter accumulation models were obtained as follows (Fig.2.5, Table 2.6):

Y1=280.7/(1+ 737.6 exp (-0.07t))
Y2=268.3/(1+ 1430.6 exp (-0.078t))
Y3=172.7/(1+ 235.2 exp (-0.76t))

Table 2.6 Parameters for the models of dry matter accumulation of sorghum plants

Variety		K Environmental		Maximum	growth	biomass (day)	duration
	a	b	capacity	R	Initial period growth rate
	(g/plant/day)		(g/plant/day)		(g/plant)
Shennong No.2	737.6	0.707	280.7	0.9972**	4.91	0.37	140
Rio	1430.6	0.078	268.3	0.9984**	5.18	0.18	145
Jinza 4	235.2	0.076	172.2	0.9955**	3.27	0.73	125

Table 2.6 and Fig.2.5 showed that the dry matter accumulation of sweet sorghum had three features as compared with that of grain sorghum:

(1) The higher peak value of the accumulation of dry matter. From Fig.2.5 it could be found that the fastest period of dry matter accumulation of sweet sorghum, called the high peak stage of dry matter accumulation, was at t= - ln (1/a) /b. At this time the accumulated dry matter of a plant just was half of its last dry matter (K1 (1/2), K2 (1/2), K3 (1/2) in Fig.2.5), which appeared about 70 days after emergence (heading period), in Jinza 4 and over 90 days after emergence, about one week before heading, in Shennong No.2 and Rio. It was clear in Fig.2.5 that the peak value of sweet sorghum was higher than that of grain sorghum in dry matter accumulation. For example, the highest rates of the dry matter accumulation were 4.91 g/plant/day and 5.18 g/plant/day respectively in Shennong No.2 and Rio, which were 50.15% and 58.14% higher than that of Jinza 4.

(2) The higher rate of the accumulation of dry matter at the late stages of the development. The rate of accumulation of dry matter was still higher after heading in sweet sorghum. In two varieties, Shennong No.2 and Rio, individual average growth rates decreased only by 10% as compared with the peak value from peak stage to mature stage but decreased by 44% in Jinza 4 (1.83g/plant/day).Therefore about 50% of dry matter could be produced during 1/3 of the late stages of development in sweet sorghum.

(3) The higher biomass of individuals. Individual and population biomass were higher in sweet sorghum than those in grain sorghum because of a higher peak value of the accumulation of dry matter and a quicker speed of the accumulation of dry matter at the late stage as well as longer duration of the two varieties used in the study .The individual biomass of Shennong No.2 and Rio was 163% and 155% of that of Jinza 4 respectively (Table 2.7)

Fig. 2.5. Models for the accumulation of dry matter in sweet and grain sorghum plants Y1 Shennong No.2, Y2 Rio, Y3 Jinza 4

Table 2.7 Comparison of biomass of sweet and grain sorghum

Variety	Biomass of plant (g/plant)	Biomass (Kg/ha)	Grain yield (Kg/ha)	Economic index
Sweet sorghum
Rio	292.40	21120.00	3300.00	0.155
Shennong No.2	312.92	23508.00	4809.75	0.210
Grain sorghum
Jinza 4	183.55	19386.75	8542.65	0.440
Shennong 447	156.89	17724.45	8152.50	0.440

b) Distribution of dry matter and formation of yield

(1) Distribution of dry matter

We made researches on the source sink relationship between dry matter distribution and organs in sweet and grain sorghum by using the distribution rate of dry matter. The results showed that photosynthate of grain sorghum were mainly distributed to leaf and sheath before elongation; the distribution rate of stalk began to go up after elongation and that of panicle occupied a dominant position after heading. The distribution rates of leaf, sheath and stalk were negative values after anthesis but that of panicle rose rapidly and its value reached over 100%. Afterwards the rates of leaf, sheath and stalk went up and became a positive value as the rate of panicle went down. The distribution rates of leaf, sheath and stalk had negative values because their photosynthate was transported to panicle.

In comparison with grain sorghum, the distribution of dry matter of sweet sorghum was of four following outstanding features:

A. The higher distribution rate and the longer duration of distribution of the dry matter of stalk. The distribution rate of sweet sorghum centred on the stalk, and the duration of stalk distribution in the first place lasted longer in its whole life, which was about 50 days, (but 30 days or so in grain sorghum) that is, from the 60th to the 110th day after emergence. The maximum distribution rate was up to 60 - 80% of the whole plant (but 40 - 55% in grain sorghum). The distribution rate of dry matter of stalk always was maintained to be positive in its all life, which was different from grain sorghum.

B. The coexistent time of the vegetative growth and the reproductive growth lasted very long and almost from the elongation to the maturity. In general the distribution of matter of cereal crop takes leaf as the centre of growth from emergence to elongation, stalk as the new centre of growth after elongation and panicle as the centre of growth after heading, merely the reproductive growth, meanwhile leaf and stalk stop growing basically. However, sweet sorghum is not so. Stalk and panicle grew together from the elongation in sweet sorghum. Stalk was the main centre of growth but panicle was the secondary one from the elongation to the heading. The panicle became the main centre of growth but stalk was the secondary one after heading. The two kinds of growth matched side by side from the elongation to the maturity at which time the amount of the accumulation of dry matter in stalk and panicle rose to the maximum value simultaneously.

Therefore, sweet sorghum was in the state of simultaneous growth of the vegetative and reproductive organs, which lasted above 80 days that accounted for 60% of whole duration of development. The amount of the accumulation of dry matter in stalk did not decrease but increase with the increase of that of panicle in sweet sorghum.

C. Sweet sorghum was a kind of crop with two sinks. Fig.2.6 suggested that the distribution rate to leaf was at the highest level at the seedling stage. The leaf was not only a source for the production of dry matter, but also a sink for the photosynthate at the stage. From the elongation to the heading, much photosynthate was distributed to stalk but little to panicle, which showed that stalk was the main sink but panicle was the secondary one. Meanwhile, the distribution rate to leaf and sheath decreased gradually to change into unitary source. During 10 days after heading, the distribution rate to panicle increased linearly so that panicle became the main sink, but the rate to stalk decreased so that stalk became the secondary one .It could be found that stalk had become the first centre of growth and the sink of photosynthate from the 60th day after emergence on, which lasted above 50 days. After heading stalk became the secondary one which lasted more than 30 days. That is, the time when stalk was the centre of growth accounted for 80 days before and after heading, which was longer than that of panicle. Stalk and panicle were all sinks of the photosynthate in terms of the relationship between source and sink in sweet sorghum. Therefore, sweet sorghum was a kind of crop with two sinks of photosynthate.

D. The ratio of stalk was large. Because of the longer time of the growth of stalk, the higher rate of distribution of dry matter to stalk, and longer duration when the rate kept the maximum value among organs lasting from the elongation to the maturity, the final ratio of dry matter among the different organs was stalk> panicle > leaf> sheath. (Fig.2.6 and Table 2.8).

(2) Formation of yield

A. The model for the formation of yield in stalk. The rate of the accumulation of dry matter of stalk in sweet sorghum was sped up after the elongation and was the fastest around the heading. The main difference between sweet sorghum and grain sorghum was that the dry matter weight accumulation of sweet sorghum did not reduce but increase after heading and the increment lasted till maturity although the speed of the increase was a little reduced. Therefore, This was the obvious feature of the yield formation of stalk. The last stalk harvest index was 0.55 - 0.60 which was 213-232% of that of grain sorghum Its models were S curves. But the dry matter weight of grain sorghum reduced gradually after heading and increased slightly before maturity, so the cubic polynomials were built (Fig 2.7).

Y1=208.60/ (l+ 1268.18exp (-0.082t)) (r=0.9923**; n=7)
Y2=193.45/ (l+ 6410.50exp (-0.0915t)) (r-0.9128**; n=14)
Y3=-196.647+ 7.457t-0.0803t2+ 0.0002877t3 (r=0.9823**; n=7)
Y4=-259.558+ 10.480t-0.124t2+ 0.00047t3 (r=0.9630**; n=7)

B. The model for the formation of yield in panicle. Since the panicle developed late and the speed of the increase of dry matter was slower, the final harvest index of grain was smaller in panicle of sweet sorghum. The means of the harvest indices were 0.155 and 0.210 in Rio and Shennong No.2 respectively. The yield of the panicle or the grain of sweet sorghum was 38.5-55.7% lower than that of grain sorghum at the similar biomass. The model for the formation of yield of panicle in sweet sorghum was as follows:

Y1=69.94/ (1+ 7555.26exp (-0.1506t)) (r=0.9705**; n=7)
Y2=58.35/ (1+ 1733.5exp (-0.0951t)) (r=0.8420**; n=13)
Y3-107.46/ (1+ 9984.30exp (-0.1556t)) (r=0.9367**; n=18)

For the above mentions the chart of formation of yield in sweet and grain sorghum were drawn (Fig.2.9). Clearly, stalk yield far exceeded grain yield in sweet sorghum. There was an obvious difference in formation of stalk and grain yields between sweet and grain sorghum.

Fig. 2.6a. The distribution rate of dry matter in sweet sorghum (Shennong No.2) (Jinza 4)

Fig.2.6b The distribution rate of dry matter in grain sorghum

1. Stalk, 2. Panicle, 3. Sheath, 4. Leaf

Table 2.8. Proportions of dry matter weight of different organs in sweet and grain sorghum (%)

Variety	Panicle	Stalk	Leaf	Sheath
Sweet sorghum
Shennong No.2	26.16	53.68	13.30	6
Rio	15.26	60.28	14.37	9.64
Grain sorghum
Jinza 4	57.12	23.28	11.74	7.86
Shennong 447	57.70	23.77	12.12	8.59
Liaoza 1	52.09	24.78	11.37	7.53

Fig. 2.7 The Formation of yield of stalk in sweet and grain sorghum Y1 Shennong No.2, Y#2Rio, Y3 Jinza 4, Y4 Shennong 447 T is the days after emergence

C. The formation of yield of sugar of stalk. Solvable sugar is mainly stored in the stalk and the saccharinity is a main parameter of the products of sweet sorghum. The main stages of sugar! !accumulation appeared after heading, and the most important stage of which appeared 10-20 days after the heading and saccharinity reached the highest level at maturity. The mean saccharinity of whole plant was 14.9-16.3%, of which the value was higher in Rio than in Shennong No.2.

As for the sugar of all internodes it increased with the development course and was the fastest increase between the heading and the 20 days after heading. And then the increase became steady and the saccharinity rose gradually and got to a high peak at maturity while the dry matter weights of stalk and panicle were also maximum. The vertical distribution of saccharinity was that the upper-middle was higher than the middle-lower in all internodes among which the 5-7th of the upper (from top to bottom, the following was same) was the highest (Fig.2.10). Between the sugar contents and dry matter weights of all internodes showed positive correlation. The vertical distribution of sugar contents of them just was contrary to that of saccharinity, that is, the middle-lower was higher than the upper-middle among which the 11th was the highest and from 11th on the sugar contents reduced little by little upward and downward (Fig.2.10)

Fig. 2.8. The formation of yield of panicle in sweet and grain sorghum Y1 Shennong No.2, Y2 Rio, Y3 Jinza 4 T is the days after elongation

Fig. 2.9 The chart of formation of yield in sweet and grain sorghum (a. Shennong No.2, b. Jinza 4) A. Panicle, B. Stalk, C. Leaf and sheath

2.2.4 Discussion

The research on sweet and grain sorghum indicated that there are great differences between them in the accumulation and distribution of dry matter as well as the formation of yield. These special phenomena and laws of sweet sorghum are of new revelation in the cultivation and breeding of crops.

Sweet sorghum is a kind of crop with two sinks. From this point it differs from common crops of cereal and legume. So deeply studying the features is important to create some of striking advances on the study of the concepts used in the past about the productivity of crop, the formation of yield of crop, the theories of growth and development of plant and the balance among organs of plant. This will bring some new ideas to exploit new genetic resource of crop breeding and to decide the next aim of the breeding.

Fig.2.10 Content of sugar, dry matter weight and saccharinity in each internode (Rio)

As sweet sorghum has some special features, the traditional methods for management in cultivation must be broken and stress should be placed on how to regulate the relationship of two sinks and the relationship between reproductive growth and vegetative growth. The key to the cultivation of sweet sorghum lies in how to promote early emergence and fast development at early stage, to strengthen management at late stage and to diminish the competition of nutrition and water between stalk and panicle. In this way the aim is to gain both higher sugar yield of stalk and grain yield.

Sweet sorghum possesses two kinds of economical organs of stalk and panicle. The use of this genetic resource makes the economic value of production of dry matter of crop increase many times and proposes a new demand for the breeding of new varieties. That is to say, a new variety not only has a strong reproductive organ but also the maximum of total of dry matter production. Therefore we should not only pay attention to the matter production but also to the suitable distribution of matter and balanced development of organs.

2.3. Inheritance of sugar content in sorghum stalk

Sorghum stalk can be generally divided into two types. One is dry type, when plant matures with little juice in the stem, which the other type is full of juice. Sweet sorghum belongs to the second type, and it contains some sugars in its sap. Usually sorghum with over 8 °BX of sugar in the juice is called sweet sorghum. The main component of the sugar in sweet sorghum stem is saccharose. Sweet sorghum has been used for producing sugar, fermenting, and making forage. Sweet sorghum also possesses high photosynthetic efficiency and high biomass yield, so it has become more attractive in agricultural production.

There has been some reports about the inheritance of sugar content of sweet sorghum stalk. Non- sweet is dominant which is controlled by a couple of X and x genes (Ayyangar, 1936). Until now many researches on sugar inheritance in sweet sorghum stalk including Cheng's recent research (1986) are all limited within the hybridization between sweet sorghum varieties. Sweet sorghum is characterized by small grain and low grain yield. Many sweet sorghum varieties lately introduced from foreign countries such as Rio, Wray and Keller, though have high biomass, their grain yield is only about 1500kg per hectare. According to our country's character of high population and small farmland, the sweet sorghum with both high grain yield and high sugar content in juice of stem should be bred to not competing with food production. The hybridization between sweet type and grain type varieties has been conducted to transfer the characters of grain sorghum such as bigger kernel weight, better panicle and larger head weight into sweet sorghum. Under such situation, it is obvious that research on sugar inheritance of hybridization between sweet sorghum varieties is not enough. We should understand the heredity of sugar under hybridization between sweet sorghum and grain sorghum involving dry type. This article has been written on this research report.

2.3.1 Material and Method

Varieties studied in this research, include grain varieties of dry type Shanchishan and Xinliang52, grain sorghum of low sugar content in juice of stem Jingliang5, Xinliang7 and early maturing Hegari, sweet sorghum Roma with high sugar content in juicy stem.

Hybridization between sweet and grain varieties such as combinations of Xinliang7 x Roma, Jingliang5 x Roma, early maturing hegari x Roma, Shanchishan x Roma and Xinliang52 x Roma.

The parents, F1 and F2 were planted in 1987, and F3 was planted in 1988. The experiment was conducted in the farm of Shenyang Agricultural University. The parents, F1, and F3 lines were each planted in a three line plot, each line involved 20 plants. 300 plants were required for each F2 population. The distances between plants and rows were 25cm and 60cm respectively. When kernel showed black tier, the sugar content was to be measured using handle sugar tester made in China and the mean of sugar contents of the second, third and fourth nodes from head was calculated as a sugar value of the plant in ° BX degree . Because dry type of stalk shows dominant to juicy type , so Shanchishan, Xinliang52 and their Fl belong to dry type, thus their sugar contents in the stem can not be measured. But their genes controlling sugar content can be detected from the segregation of F2 population from the hybridization between dry and juicy types. For example, the Fl of combination Xinliang52 x Roma was completely dry stem without any juice. The segregation of stem types was investigated on 300 plants of the F2 population and found 231 plants of dry type, 69 plants of juicy type, which corresponded with the ratio of segregation 3: 1. According to the result of X test, this trait was controlled by one pair of genes and dry type was dominant and juicy type was recessive. The sugar content of F2 was measured from the 69 juicy plants.

Formulas used in the research:

H= [Fl-0.5 (p1+ p2)] / [0.5 (p1+ p2)]

Where H is average heterosis, F1 is hybrid, PI and P2 are the parents in each combination.

h² (B) = [VF2-(Vp1+ Vp2+ VF1) /3] /VF2

Where h2 (B) is broad heritability, VF2, VF1, VP1 and VP2 represent phenotype variance of population F2, F1 and parents respectively.

b=(S XY-S XS Y/N)/[S X²-(S X)²/N]

Where b is regression coefficient.

Where r is correlation coefficient.

2.3.2 Result and Analysis

(1) Sugar content in sorghum stem belonging to quantitative inheritance controlled by minute multiple genes

According to figures in Table 2.9, the variance of F2 in five combinations surpassed that of parents and F1, which indicated that there was wide segregation in the F2 population.

Tab.2.9 Sugar degrees in stems of parents, F1 and F2 populations for 5 combinations

 

Combination	Parents and Number progenies of plants tested		X	S	s 2	h2B	I*	H
Xinliang7 /Roma	Roma	58	14.03	1.59	2.542
	xinliang7	10	6.50	1.39	1.953
	F1	9	8.92	1.98	3.935	0.65	86.89	-13.1
	F2	178	11.96	2.82	7.998
Jingliang5 /Roma	Roma	58	14.03	1.59	2.542
	Jingliang	10	4.43	0.42	0.173
	F1	12	8.20	1.12	1.250	0.79	88.80	-11.2
	F2	153	9.18	2.51	6.300
	Roma	58	14.03	1.59	2.542
Early hegerui /Roma	Early hegerui	14	7.98	1.56	2.430
	F1	9	9.90	2.05	4.203	0.81	90.0	-10.0
	F2	48	10.95	4.01	16.080
Shanchishan	Roma	58	14.03	1.59	2.542
/Roma	F2	51	14.18	2.41	5.799
Xinliang52	Roma	58	14.03	1.59	2.542
/Roma	F2	44	12.89	3.20	10.266

* Index of heterosis

Fig. 2.11 showed the distribution curves of sugar contents of the parents, F1 and F2 of combination Xinliang 7 x Roma were normal. The distribution of sugar degree of parent, Xinliang 7, ranged 4-9, the parent, Roma, ranged 10-18 and F1 ranged 5.5-11.5. The distribution of F2 was wider than others, from 6 to 18.5. This was mainly caused by segregation of genes besides environment effect.

Fig. 2.12 showed distribution curves of sugar degree of Roma and its combination with Xinliang 52. Xinliang52 belongs to dry type and its sugar degree can not be measured. The wide segregation of F2 of the combination Xinliang 52 x Roma reflected gene recombination, leading to many genotypes. Comparing the variation in Table 2.9, F2 was 10.267, Roma was 2.5415, variation of F2 was four times of Roma, and the mean of sugar degree in F2 was 12.893 lower than that of Roma, 14.034. Thus, the genotype controlling sugar degree of Xinliang 52 can be known from the figures and the curve of segregation in the F2. It was the same as that of Xinliang 7 with low sugar degree in stem.

Fig. 2.11. The distribution curves of sugar contents of the parents, F1 and F2 of combination Xinliang 7 x Roma

In the combination, Shanchishan x Roma, although X values of were not significantly different between F2 and Roma. The variate of F2 was one time higher than that of Roma. This proved the meaning of the X was different for the F2 and Roma and showed that the diversity of Sugar degree in F2 population was caused by the gene recombination between Roma and Shanchishan besides environment effect . This also showed that the genotype controlling sugar of Shanchishan was different from Xinliang 7 and Xinliang 52, which could lead to high sugar degree.

From above analysis, it is obvious that, if only one parent belonged to sweet sorghum, the sugar degree of F2 population can be measured. The sugar degree of F2 population with wide continous variation and normal distribution showed that sugar content was controlled by minute multiple genes.

Fig.2.12. The distribution curves of sugar degree of Roma and its combination with Xinliang 52

(2) The genes controlling low sugar content was partially dominant

The sugar degrees of F1 from 3 combinations in which the parents were juicy type were lower than the average value of their parents. For the F1 in combination, Xinliang 7 x Roma, it's average of the sugar degree was lower than both parents by 1.345, in other combination, Jingliang 5 x Roma, the sugar degree of F1 was lower than both parents by 1.03, and F1 in combination, early mature Hegari x Roma was lower average value of both parents by 1.1. Therefore, their average heterosis of F1 was negative value, -13.1 %, -11.2 % and 10 % respectively. This proved that genes controlling low sugar content were partially dominant, the genes controlling high sugar content were recessive. This also proved that sugar degree in stem can not be improved by heterosis breeding.

According to genetic theory the plant with recessive homozygote of gene in F2 population would appear and plant with high sugar degree in F2 population could be found.

Therefore, the X value of sugar degree of F2 appeared higher than that of F1. The three combinations all showed that the value of F2 was higher than F1, which was the best proof of recessive genes increasing sugar degree.

(3) The analysis of heritability of sugar degree in stalk

The broad heritability of three combinations in which the parents were juicy type, Xinliang 7 x Roma, Jingliang 5 x Roma and early maturing Hegari x Roma was calculated through variate of their parents, F1 and F2, they were 0.65, 0.79 and 0.81 respectively and the average value was 0.75. The sugar degrees of plants in F2 and F3 lines were compared and the result was that sugar degree of F2 was 12.71 and that of F3 was 12.43, the regression coefficient, b=-0.3226, and regression formula, a=Y-6X= 16.53, just as shown in figure 3. The value was significant for the regression relation, which indicated that sugar degree in stem of sorghum was determined by additive effect of gene.

The broad heritability of sugar degree in sorghum stem was not high, which showed that the character was easily changed by environment. The effect of nitrogen content in soil on sugar content in stem of sweet sorghum was observed in the our research. For example, for sweet sorghum variety, Roma, which was planted in soil lack of nitrogen, its sugar degree was over 16 °BX, but in rich nitrogen soil the sugar degree was only 14 °BX.

Because sugar degree is mainly determined by additive effect of gene and because the trait of high sugar content is recessive, high sugar content of F2 plants can be steadily inherited. For this reason, plants with high sugar degree can be selected in the early generation of breeding, but the growing condition of plant should be equal.

(4) The correlation between sugar degree in stem and other characters

Ten plants from each combination, a total of 50 plants were sampled to measure sugar degree, plant height, date in blossom and kernel weight, then the correlations between sugar degree and other characters such as 1000 kernel weight, plant height and blossom date were calculated and the correlation coefficients were -0.472, 0.007 and 0.2749 respectively. The t values were measured indicating that the correlation coefficient between sugar degree and 1000 kernel weight was very significant, but the other two were not significant. All these belonged to the correlation of phenotype because the measurements were made for the phenotypes of F2 plants. From the results, it could be found that there was no any correlation between sugar degree in stem and plant height or blossom date. But significantly negative correlation between sugar degree and 1000 kernel weight had been found, which showed that the plants with high sugar degree in hybridization offspring had low kernel weight. This seemed to be the reason why sweet sorghum had small seeds, Chao pointed that the 1000 kernel weight of sweet sorghum was always lower than 20g. In our research on sweet sorghum, 57 varieties from China and abroad were investigated and we found that only 21 % varieties had their 1000 kernel weight surpassed 20g, 3.5 % varieties surpassed 30g. In order to select the plants with both high sugar content and high kernel weight from hybridization offspring large population was required.

2.3.3 Conclusion

(1) Sugar content in stem of sweet sorghum was determined by multiple genes with minute effect and the trait belonged to quantitative inheritance of additive gene effect. The gene controlling low sugar content appeared to be partially dominant.

(2) Large population of hybridization offspring was necessary for screening plants with high sugar content and high kernel weight because negative correlation existed between sugar degree and kernel weight.

(3) The generations with high productivity of grain and high sugar degree in stem can be selected through gene recombination from hybridization between grain sorghum and sweet sorghum. Such materials have been obtained in our breeding program.

2.4. Research on alcohol production of stalk for several sweet sorghum varieties

There is high sugar content in juice of sweet sorghum stalk. Saccharose, fructose and glucose are the main components of the sugar. Sweet sorghum belongs to C4 crop and has high photosynthetic efficiency. So in recent years, sweet sorghum has become an attractive biomass energy resource. Many countries, such as the united states, Brazil and Germany have exploited the sugar in sweet sorghum stalk to produce alcohol fuel. Such research has also been conducted in China. Sweet sorghum varieties, Rio and Roma were introduced from the united states in 1974 and Wray, Keller were also introduced in the past several years. Several important things such as the variety adaptation, the relation between alcohol output and sugar content, and the best harvest time should be studied in order to use sweet sorghum to produce alcohol fuel in China. In this article we will report the preliminary result of the research on the aspects mentioned above.

2.4.1 Material and Method

In 1985, eight sweet sorghum varieties were planted on 11 May in a randomized block design with three replications in the farm of Shanyang Agricultural University. Each plot included seven rows that were eight metres in length and spaced 0.6 metre apart. Plant population was 5 plants per linear meter. Fertility of soil in the experiment field was moderate. Samples were taken from two middle rows on Sept. 18, Sept. 28 and Oct. 7 respectively. The fresh weights of whole plant, stalk and leaf were tested respectively, then the stalk juice was extracted and sugar degree of the juice was measured. The content of saccharose, fructose and glucose was measured with liquid-phase chromatography in the Physical and Chemical Test Center of Liaoning.

The process of fermentation:

(1) Culture in slant medium: Original spawn 102 was from Jilin Sugar Plant and it was reserved in freezer. In the fermentation the original spawn was inoculated on slant medium consisting of rice koji extract to grow in 28-30 °C for 3-4 days.

(2) Liquid culture: The spawn cultured in slant medium was to make suspension liquid of germ and inoculated into the sterilized juice of sweet sorghum of 100 ml and to culture in 28-30 °C for 24 hours.

(3) Extension culture: The germ liquid from second step was inoculated into sterilized sweet sorghum juice, with the ratio of 1: 5. The culture of fermentation was conducted in flask in 28-30 °C (pH=5) for 38 hours.

(4) Distillation: The liquid of fermentation was distilled through conventional method and the alcohol degree was measured.

2.4.2 Result and Discussion

(1) Sugar in stem juice of sweet sorghum

According to Table 2.10 and Table 2.11, the eight varieties all possessed high sugar degree in stem juice. The sugar degree of hybrid 623A x Rio was 13 °BX at late dough stage on Sept. 18, the sugar degree of Keller was the highest, 19.5 °BX on Oct. 7. The sugar degree in stem of all varieties increased as the crops matured. Table 2.10 also showed that the sugar degree of five varieties with high biomass on Sept. 28 was higher than that of the sample extracted Sept. 18 by 5.2 %, and the sugar degree of the sample extracted on Oct. 7 was higher than that on Sept. 28 by 7.4 %. Table 2.10 showed that saccharose content in the juice of stem was highest and the content of glucose and fructose were little. Furthermore saccharose increased and glucose and fructose decreased as the crops matured. From Table 2.10 we could find that the juice rate extracted on Sept. 28 was more than that on Sept. 18 apparently. The average of five varieties increased 22% and the content of saccharose in juice increased even more dramatically. Although the fresh of weight stem also increased, such as the average of five varieties that increased 4.6 %, the total sugar content increased doubly. For example, the average of total sugar contents in stem were 3.49 % and 7.33 % on Sept. 18 and Sept. 28 respectively.

(2) The correlation between alcohol degree and sugar content

Alcohol was made from sweet sorghum stem through the fermentation process of sugar in juice of stem. Analysis on correlation showed that there was a very close correlation between the saccharose content in stem juice and alcohol degree. The correlation coefficient for the two period extractions were significant and very significant respectively. And there also were are higher positive correlation coefficients between saccharose content and total sugar content. For the sample on Sept. 18, r=0.616, and for the sample on Sept. 28, r=0.87, all were very significant, which showed the proportion of saccharose in total sugar was higher. There was a high correlation coefficient, r=0.851, between sugar degree and alcohol degree which reached very significant level for the sample on Sept. 18. Glucose and fructose all showed weakly negative correlation to sugar degree and alcohol degree. Saccharose is sweet. The sweeter of stem juice is, the more sugar degree will be, thus the sugar degree in stem of sweet sorghum can be evaluated directly by tasting and the alcohol degree of fermentation can then be deduced.

(3) Alcohol production of different varieties in sweet sorghum

The variance analysis was made for fresh stem and grain in eight sweet sorghum varieties, which showed that there was significant difference among varieties. There was no significant difference in fresh stem yields of 623A x Roma, Keller, Wray and Rio, but their fresh stem yields were higher than those of other four varieties. The grain yield of 623A x Roma was the highest among the eight varieties, significantly higher than that of 623A x Rio and very significantly higher than those of the other six varieties.

According to fresh stem and juice rate, the juice yield per hectare can be calculated, and according to alcohol degree produced from sugar, the alcohol yield from stem can also be calculated. The data from foreign countries showed that one bushel sorghum grain can produce alcohol 2.5 gallons, the proportion rate was 2.5: 1. The proportion, 3: 1, was used to calculate alcohol yield from grain in our research. Alcohol production of stem juice among Keller, Wray and 623A x Roma was similar but higher than that of other varieties. In developed countries, the stem yield was mainly concerned and attention was not paid to grain in sweet sorghum breeding, because only sweet sorghum stem with exclusion of grain was harvested by machines. In China sweet sorghum was cut by hand and grain was harvested for food or feed. In order not to compete with food production field, the sweet sorghum variety with higher grain yield and high sugar content in juice of stem was required. The hybrid, 623A x Roma, was bred just for this aim. Table 2.10 showed that the grain yields of the three varieties, Keller, Wray and Rio were low and the alcohol yields from grain were only as 1/3-1/4 as that from stem, which indicated that there was no great difference in total alcohol yield per hectare from stem and grain between the three varieties and other ones. However, the hybrid 623A x Roma not only had high stem yield but also high grain yield. So its total alcohol yield from stem and grain was significantly higher than that of other varieties in this experiment.

Table 2.10 Fresh stem yield, juice rate, sugar degree and grain yield of sweet sorghum with different harvest time

Category	Harvest time month. day	varieties					average
		Keller	Wray	623AxRio	623AxRoma	Rio
fresh stem	9.18	43215.0	44505.0	33750.0	49875.0	40657.5	42400.5
yield	9.28	46447.5	46650.0	35130.0	51412.5	42277.5	44383.5
kg/ha	10.7	49447.5	49845.0	42517.5	52102.5	47400.0	48262.5
juice rate	9.18	0.44	0.59	0.55	0.55	0.54	0.534
	9.28	0.64	0.70	0.60	0.68	0.64	0.652
	10.7	0.62	0.65	0.62	0.65	0.59	0.628
sugar	9.18	17.0	15.0	13.0	16.0	17.2	15.64
degree	9.28	17.8	15.8	15.3	16.0	17.4	16.46
(BX)	10.7	19.5	18.5	16.7	16.1	17.5	17.67
grain	9.28	1642.5	1440.0	4477.5	5040.0	2325.0	2985.0
yield kg/ha	10.7	2077.5	1826.3	4545.8	5022.0	3375.0	3369.3
alcohol yield from grain (1/ha)		547.5	480.0	1417.5	1680.0	775.5	980.1
alcohol yield from stem and grain (1/ha)		2892.5	2657.0	2658.8	4010.3	2875.5	3018.8

(4) The relation between harvest time and alcohol yield

Table 2.11 showed that the late harvest of sweet sorghum can cause increase of sugar content in stem juice, for example, the sample took on Sept. 18 was 15.7 °BX, and that on Sept. 28 was 16.7 °BX, but alcohol yield didn't change, each sample was 6.5 degree. Which seemed to show that the germ was not sensitive to sugar content.

Table 2.11. Sugar content of stem and its alcohol degree of fermentation in eight sweet sorghum with different harvest time

Varieties	sugar degree (BX)		fructose (%)		glucose (%)		saccharose (%)		total sugar content (%)		alcohol degree
	9.18	9.28	9.18	9.28	9.18	9.28	9.18	9.28	9.18	9.28	9.18	9.28
623A	15.5	16.9	1.50	0.55	2.15	0.90	4.50	9.25	2.17	6.25	4.80	4.80
623A x	16.2	16.9	0.70	0.80	1.00	1.40	7.60	9.65	3.84	7.42	6.85	6.00
Sugardrip
Roma	15.6	17.8	1.50	0.90	2.35	1.45	6.65	10.0	4.16	7.14	6.4	7.00
Keller	17.0	17.8	0.50	0.50	1.30	0.90	8.00	10.6	3.30	7.62	7.2	7.10
Wray	15.0	15.8	0.45	0.80	0.75	1.45	7.25	9.15	4.01	8.00	5.9	6.00
623A x	13.0	15.3	0.95	0.85	1.45	1.30	5.60	8.35	3.00	6.67	4.5	5.30
Rio
623A x	16.0	16.0	1.45	1.30	2.30	2.05	6.85	8.00	3.58	7.75	6.7	6.00
Roma
Rio	17.2	17.4	0.70	0.60	1.30	1.10	7.70	10.50	3.83	7.77	6.9	7.00
average	15.7	16.7	0.97	0.79	1.58	1.31	6.77	9.43	3.49	7.33	6.2

The stem and leaves of sweet sorghum were green before they were killed by frost and can photosynthesis which increased the yield of fresh stem if the temperature was suitable. The fresh stem yield of five varieties in Table 2.10 demonstrated that the yield harvested on Sept. 28 was higher than that on Sept. 18 by 4.6 %, and the yield harvested on Oct. 7 was higher than that on Sept. 28 by 8.7 %. Because the sugar degree in stem juice increased continually by delaying harvest, the sugar degree on Sept. 28 was higher than that on Sept. 18 by 5.2 %, and sugar degree on Oct. 7 was higher than that Sept. 28 by 7.4 %. The juice rate on Sept. 28 was highest, which was high than that on Sept. 18 by 22 %, however, the juice rate on Oct. 7 was lower than that on Sept. 28 by 3.7. So, in order to get high alcohol yield, the change of fresh stem weight, sugar degree and juice with mature process of grain rate must be considered and early harvest was not suitable. According to average of eight varieties the stem yield on Sept. 28 increased 26 % than that on Sept. 18, according to the grain yield of five varieties, the grain yield on Oct. 7 increased 13 % than that on Sept. 28 which showed that late harvest was benefit to late mature varieties, Keller, Wray and Rio, but there was not benefit to moderate mature variety, 623A x Rio, in increase of grain yield.

It was difficult to conserve fresh stem of sweet sorghum for long time because after of harvest the sugar content in stem juice decreased quickly with water in stem disappeared. So, in practice of production harvest in short time and store of fresh stem in long time would be avoided. After one month of blossom grain in early dough stage, sweet sorghum can be harvested, but its fresh stem weight, sugar degree and juice rate was not high and alcohol yield would be decreased. Especially early harvest was not suitable for the varieties with high grain yield, because their grain yield would be drastically decreased, therefore, it should be considered that premature varieties were combined with late mature varieties and early harvest was not suitable for late mature varieties.

2.4.3 Conclusion

(1) Saccharose was main component of sugar in juice of sweet sorghum stem. There was positive correlation between alcohol degree and degree of saccharose, in juice. There was also positive correlation between saccharose content and sugar content in juice of stem. Because saccharose possessed sweet, the alcohol degree fermented from sweet sorghum stem can be directly evaluated by tasting stem of sweet sorghum.

(2) Keller, Wray and Rio were the good varieties for producing alcohol by fermentation of stem in the foreign countries, but their grain yield was lower. Hybrid, 623A x Roma, bred by using heterosis possessed high grain yield, 5040 kg/ha, which was the highest in all varieties in the experiment, its grain yield on Sept. 28 was one time as that Rio and two times as that of Keller and Wray. The alcohol yield from stem of 623A x Roma reached or surpassed that of Keller, Wray and Rio.

(3) Although the late mature varieties had high sugar degree in the early double stage, the stem yield, sugar content and juice rate would still increase with the grain maturity. So it was obvious that early harvest was not suitable for varieties with late maturity. In order to extend the duration of fermentation, the premature variety should be combined with late mature variety in the practice of production.

2.5. Sweet sorghum production by multiple cropping with early maturing crops

China is a country with large population but small per capita farmland, just as much as one third of the world average. So, it is very important to fully tap the potentialities of the farmland in agricultural production. In fact, Chinese people have the tradition of intensive cultivation since a very long time ago. As early as two thousand years ago, there was recorded multiple cropping format of different crops in China. In recent years, along with the deepening reform in cropping systems intercropping or interplanting has developed rapidly and many new patterns with advanced techniques have been created. Take Liaoning Province as an example, maize intercropping with soybean was once very popular, with unfixed row ratios depending on the objectives and growth conditions. In recent years, maize intercropping with wheat has developed rapidly, and higher yield has been obtained, with row or area ratios of maize and wheat 1:1, 2:1 and 3:1. Obviously, the higher yield are gained with the contribution of edge effect of maize when it is intercropped with short stalked soybean or early sown spring wheat. The intercropping populations are also good for the fully utilization of sun light, heat and the farmland, therefore increasing the total product of per unit area of land.

Sweet sorghum is long stalked plant that has edge effect too when intercropped with short stalked plants. Therefore, we launched the studies on sweet sorghum intercropping with potato consulting the experience of maize intercropping with short stalked plants.

Sweet sorghum is suitable to intercropping with early maturing crops for its characters in growth and development. As originated from the tropics, sorghum is a thermophilic crop. If it is sown too early in the northeast of China, the seeds are more liable to turn deterioration because of the low temperature. The adapted sowing date is the early May when the mean soil temperature at 5 cm position below the ground has steady passed 10 °C. Sorghum sown in spring requires about 160 °C accumulated temperature of 10°C from sowing to emergence, with a time over 10 days. Sweet sorghum seedlings develop slowly at their early stage. Most sweet sorghum varieties are late maturing or long growing. Jointing stage is reached no early than 12 leaf stage. About 680 °C accumulated temperature or 40 days are required from seedling emergence to jointing stage. At jointing stage, the natural height of plants is about 30 ~ 40 cm, with leaf area index of about 2.5, therefore the ground is not shaded by leaves very much. Sweet sorghum grows vigorously following jointing stage, a newly developed leaf being present in about every 3 days, about 10 cm of plant height being increased each day for a short period, and leaf area index increasing rapidly. The plant height may reach about 300 cm and the leaf area index may be over 5 when sorghum at flowering stage. So, sweet sorghum is not suitable for high density, the recommended density is about 70000 plants/ha. It is known from the discussion above that sweet sorghum can not fully utilize the solar radiation in its early growing stage because of its slow growth and small leaf area. The adult sweet sorghum is very long stalked with long and broad leaves, which makes it more capable of giving fully play to the edge effect.

Potato and wheat is a cool-loving crop that can be planted in early April and harvested in early or mid July with a substantially high yield.

Until mid or late June when sweet sorghum begins jointing and grows up at only 30 ~ 40 cm in height, the intercropped sorghum does not have shading effect over potato or wheat, and the potato or wheat can develop vigorously. When sweet sorghum begins developing luxuriantly and has higher leaf area index after mid or late June, potato or wheat has been already harvested, so the rows in which once potato or wheat grows become the empty rows like cropping edge of sweet sorghum. In this case sorghum can give fully play to the edge effect because of the broadened space easier for air diffusion and light penetration, consequently grows normally and produces nearly the same yield as monocropped sorghum even though it has fewer rows and is seeded at smaller distance in the row. This proves that by using suitable cropping patterns according to the different ecological properties of sweet sorghum and potato in the growth and development the heat, light and soil resources can be fully utilized, therefore high yield can be obtained.

The sowing date of potato could be moved up to mid or late March in the condition of covered soil with plastic films, ensuring that potato will mature in mid or late June and that it can be reaped in time. Early maturing sweet sorghum hybrids can be planted then as a succession crop in multiple cropping with potato. The studies showed that higher yield was obtained in this cropping pattern.

2.5.1 Sweet sorghum and potato production in intercropping

Sweet sorghum hybrid Shennong No.2 (developed in Shenyang Agricultural University) and potato cultivar Dongnog 303 (developed in Northeast Agricultural University) were used in this study. The experimental plots were arranged in a randomized complete block design each with three replications. Each plot consisted of twelve 10 m rows spaced 0.60 m apart. Sweet sorghum and potato were planted in a row ratio of 2: 1. Monocropping sorghum was planted as control. Potato was sown on 15 April with 23 cm apart between plants; sorghum was sown on 5 May. Ammonium di-hydrogen phosphate of 150 kg/ha was applied along with sorghum planting as the seed fertilizer. No any irrigation was provided in the experiment.

Potato emerged on 8 May and grew sturdily. It came into squaring stage by 10 June when a large number of tubers had formed and some had been 2 ~ 3 cm in diameter.

Table 2.12. Fresh and dry weights tested on 23 June and 2 July in intercropped and monocropped sorghum

Replication Treatment		23 June		2 July
		Fresh weight (g/plant)	Dry weight (g/plant)	Fresh weight (g/plant)	Dry weight (g/plant)
I-1	Intercropping	37.5	5.5	149.6	21.7
I-2	Intercropping	59.0	9.0	107.6	16.0
I-3	Intercropping	51.0	7.1	124.5	17.0
I-1	Monocropping	73.2	12.1	152.4	20.6
I-2	Monocropping	107.0	12.2	204.2	28.1
I-3	Monocropping	71.5	9.1	155.1	19.1
II-1	Intercropping	57.5	7.3	247.8	32.1
II-2	Intercropping	53.0	7.2	234.1	31.5
II-3	Intercropping	67.9	8.7	183.1	21.1
II-1	Monocropping	35.0	4.6	177.0	20.8
II-2	Monocropping	45.2	5.4	209.0	24.2
II-3	Monocropping	39.1	5.1	154.6	17.0
III-1	Intercropping	83.0	10.6	185.1	23.5
III-2	Intercropping	71.0	9.0	171.1	20.5
III-3	Intercropping	90.1	11.1	223.0	29.2
III-1	Monocropping	70.0	8.8	103.2	10.9
III-2	Monocropping	50.0	6.9	207.5	26.7
III-3	Monocropping	70.0	8.7	246.0	29.2
Mean	Intercropping	63.3	8.4	180.6	23.6
Mean	Monocropping	60.5	8.0	178.0	21.8

Sweet sorghum emerged on 15 May and was thinned at 6 leaf stage. The distance between sorghum seedlings was 25 cm for monocropping and 16.5 cm for intercropping, but both had the same plant density.

Both potato and sweet sorghum developed vigorously after mid or late June, when potato had luxuriant branches and leaves with plant height over 40 cm, and when sorghum had come into 11~12 leaf stage with plant natural height approximately 30 cm. Fresh and dry weights of monocropped and intercropped sweet sorghum were measured on 23 June and 2 July (Table 2.12). The results showed that there was no significant difference between the two cropping patterns of sweet sorghum, indicating that potato had little negative influence on sweet sorghum growth. It was also seen that sweet sorghum grew rapidly and the dry weight doubled and redoubled during that period.

Potato was harvested by stages. The average yield per plant was 320 g when potato was harvested on 2 July 54 days after emergence. It became 365 g when harvested 6 days later on 8 July 60 days after emergence. Compared with the first harvest, there was a yield increase of 14%, illustrating that the tubers grew rapidly during that period. For the last harvest on 25 July, the average yield per plant was 495 g, with an increase by 35.6% compared with the harvest on 8 July.

Plant natural height of Shennong No.2 was about 150 cm on 8 July, when the potato rows had been shaded by sorghum leaves. The light intercept by potato leaves was severely affected, and in addition it was getting rainy season and sometimes with days of continuous cloud and rain. However, the potato tubers developed rapidly during that time.

Shennong No.2 came into bloom on 11 August when the leaf area index was maximum. The intercropped sorghum and monocropped sorghum had the leaf area indices of 4.77 and 5.54 respectively.

Sorghum was reaped on 26 September. The yields were showed in Table 2.13 Although sweet sorghum produced less fresh stalk, 6000 kg/ha reduction, which seemed bad for alcohol production, the extra 10875 kg potato was gained.

Table 2.13. Yields of intercropping and monocropping Shennong No.2 sorghum and potato in fresh weight

	Sweet sorghum	Potato tuber Stalk
	Whole plant
	(kg/ha)	(kg/ha)	(kg/ha)
intercropping	69241	52215	10875
Monocropping	80048	58523

2.5.2 Multiple cropping using early maturing sweet sorghum with potato

Early maturing sweet sorghum 623A/1738 is also a hybrid with short growth period and high yield potential. It can be planted on 20 June and will reach maturity 95 days after emergence in Shenyang. Grain yield of 7500 kg/ha was obtained in this study. The plant height is 200 cm. At the time of maturity the plants still stayed green, and the fresh stalk yield reached 37500 kg/ha. The juice extraction rate was 53%, and the sugar content in the juice was 12 indicated as BX.

In the condition of plastic film covering cultivation, potato may be seeded in late March and emerged before late April. As covering cultivation is conducive to increasing soil temperature and maintaining soil moisture, potato grows rapidly. Early maturing potato may produce a yield of 26250 kg/ha when harvested in the end of mid June.

In summary, the cool weather in early spring is suitable for potato growing, while the warm weather since June is suitable for the growth of summer planting early maturing sweet sorghum. By multiple cropping with potato and early maturing sweet sorghum, 7500 kg/ha grain, 37500 kg/ha sweet sorghum fresh stalk and 26250 kg/ha potato can be harvested. In view of alcohol production, the yield per hectare in multiple cropping is much higher than in monocropping sorghum or in intercropping sorghum plus potato.

The cultural technique is not complicated. In order to ensure planting immediately after soil thaw in early spring, the field should be prepared in the previous autumn by applying base manure in amount of 30000 kg/ha and making ridges by 60 cm apart. The potato seeds are to be conducted accelerating germination before sowing. The distance between plants maintains 25 cm in the row. The ground is covered using plastic film following seed sowing. When potato seedlings emerge, small holes are artificially drilled on the film letting seedlings grow out, with the other parts of the film undamaged.

Potato is to be harvested before the end of mid June, and the field preparation is carried out immediately to ensure that the early maturing sweet sorghum is seeded no later than 20 June. The row distance is 60 cm and plant spacing in the row is 17 cm, with a density of 97500 plants/ha. Since the temperature is high in summer season, sweet sorghum grows very rapidly. It takes only about 50 days from emergence to flowering. So, agronomic measures should be taken by providing sorghum sufficient water and fertilizer to ensure early maturity and high yield. In sowing time, 150 kg ammonium di-hydrogen phosphate per hectare is to be applied as seed fertilizer. The sorghum should be thinned at 4 ~ 5 leaf stage. Top application by the amount of about 450 kg ammonium sulfate per hectare is made at 8 ~ 9 leaf stage. If drought condition is encountered during seedling stage, irrigation will be necessary.

There is no aphid injuries in summer planting sorghum, and corn borer injuries are very light. There are also no smut and leaf diseases. Thus summer planting is very favorable to sorghum growth and development.

2.5.3 Intercropping and or multiple cropping using early maturing sweet sorghum with spring wheat

A success has been obtained on the intercropping and or multiple cropping using early maturing sweet sorghum 623A/1738 with spring wheat. The wheat produced 6000kg/ha grains under the condition of moderate irrigations, and the sweet sorghum produced higher yields than it did when multiply cropped with potato as mentioned above.

Wheat was sown in the fields separated by ridges in late March. The rectangular fields are 80cm in width usually with 6 lines of wheat. There are 40cm broad border zones between the border checks. Two lines of sweet sorghum were to be planted on a border zone in mid-June, with a plant density of 97500 plants/ha.

The experiment demonstrated that for the wheat sown in border checks because the border zones were empty until its grain filling it had considerable border advantages.

The border line had a yield increase of 52.9%, the line next to the border one had a yield increase of 25.0%, and the third line increased by 7.3%. The mean increase was 28.4%. Therefore, even though the border zone occupied 1/3 field area the grain yield was nearly as much as that of purely cropped wheat.

The sorghum in the border zones was seeded at the beginning of mid-June and emerged by the end of mid-June. The spring wheat was harvested by the end of June. The wheat and sorghum had a common growth period of only about 10 days, so basically they did not affect each other. Moreover, because this summer sown sorghum was seeded several days earlier than the multiply cropped sorghum following potato, it had a higher productivity.

As for the farming managements, the summer sorghum was basically similar to the sorghum of the potato's successor.

Photo. 2.1 Intercropping cultivation of sweet sorghum with potato

2.6. The effect of different cultivation techniques on sweet sorghum

2.6.1 Sweet sorghum has features of high plant height, exuberant foliage and high biomass per plant. When the density of it is slightly higher, That will lead to the lodging and the reduction of yield easily sometimes, in addition sweet sorghum grows slowly at early stage so that time and space can not be fully utilized and the resources of light and heat are wasted. If sweet sorghum of high plant height and some crops of short stalk, or and early maturing crops of cold-resistance and short duration, can be interplanted and become a compound population, both of the utilization rates of light energy and the yield may be increased. Therefore the interplanting of sweet sorghum and sweet potato and the interplanting of sweet sorghum and pea were studied.

Rio is a variety of sweet sorghum with larger area of cultivation. It has long duration and can not ripen normally in Shenyang and Tieling with shorter frost-free period .By reason of this we adopted plastic mulch technique to promote mature and stabilize yield, which broke a new path for exploiting and using sweet sorghum in North Liaoning .

2.6.2 Materials and methods

The experiments were carried out in Shenyang and Tieling in 1985-1988. The treatments included (l) monocropping of Rio, (2) 2:2 intercropping of Rio and sweet potato, (3) monocropping of shennong-2, (4) 1:1 intercropping of Shennong No.2 and pea, (5) plastic mulch and its control and (6) leaf- cutting and head-cutting. The experiments were designs of large plot. The area was 666.7-1000m². Sampling and measurement were made once at intervals of 10-15 days from elongation on. Sampling size was ten plants one treatment each time, and then the dry matter weights of organs and saccharinity were measured. At the 30th day after heading the leaf-cutting of whole plant and the head-cutting of entire were conducted by 50-60 plants respectively. The cultivation of plastic mulch were observed once at the stages of seedling, elongation, flag leaf, heading and every 10th day after heading respectively. The items were as before.

2.6.3 results and analyses

a) Monocropping and intercropping

(1) The saccharinity of stalk and the accumulation of dry matter

Fig. 2.13 Stalk saccharinity and individual dry matter weigh (Rio)

1 .Individual dry matter weight
2. Saccharinity
3. Stalk dry matter weight
4. Panicle dry matter weight

The saccharinity of stalk was generally very low before heading, below 5% ro so, and increased rapidly after heading and the fastest increase was 10-20 days after heading. And then the increment of saccharinity became slow gradually and saccharinity got to climax between last waxy ripe stage of grain and full-ripe stage. The results of measurement showed that the last saccharinity of Rio was about 16.3% on an average, the lowest was 14.9% and the highest was 17.9%. The stalk saccharinity went up with the maturity of whole plant gradually and increased together with the dry matter weights of stalk, panicle and individual simultaneously. The maximums of accumulation of four items were almost at the same stage, the maturity stage of grain (Fig.2.13). Under the conditions of monocropping culture and intercropping the stalk saccharinity and the dry matter accumulation were of similar law on the whole.

But the growth rates of stalk saccharinity and dry matter accumulation were different between monocropping and intercropping (Fig.2.14). The two curves of growth rate of stalk saccharinity were both a kind of two- peak shape in monocropping and intercropping of 2:2, but the saccharinity of monocropping was lower than that of intercropping during all the milk stage of grain and its second peak appeared 10 days later than that of intercropping. 40 days after heading the stalk saccharinity of the former only 12.61% which was 25% lower than that of the latter on the average. However after another 10 days the saccharinity of monocropping rose quickly until its last saccharinity approached that of intercropping. The growth tendency of the accumulation of sugar and dry matter of stalk of 2:1 intercropping of sweet sorghum and pea was the same as that of 2:2 intercropping.

Fig.2.14 The growth tendencies of sugar of monocropping and intercropping (Rio)

1. 2:2 intercropping
2. monocropping

According to the dry matter accumulation of individual the growth rate of monocropping was slower and clearly lower than that of intercropping before waxy ripe stage. Especially the difference of stalk was more than that of panicle and at maturity the dry matter weight of individual of monocropping was a little lower than that of intercropping. The dry matter accumulation and saccharinity of stalk of intercropping had tended to be stable before maturity , but those of monocropping still increased clearly 10 days before maturity. All of these showed that the development course of monocropping was slow.

The accumulations of sugar and dry matter of stalk had close relationship. The dry matter accumulation of stalk was little at elongation and then sped up continuously. The accumulation of this rose sharply after heading and continued to increase all the time until fully ripe stage. Meanwhile the sugar also rose continuously with the increase of dry matter of stalk. The stalk height of sweet sorghum was generally stable a little later after heading but the dry matter and sugar of stalk still accumulated at faster speed after heading. The sugar and dry matter increased at the same time and reached maximums simultaneously from last waxy-ripe to full-ripe stage. The monocropping and intercropping had similar results, which is a striking feature of the accumulation and distribution of the dry matter and sugar of stalk in sweet sorghum.

(2) The accumulations of dry matter and sugar of internodes In Fig.2.15 the situation of sugar accumulation of stalk internodes

In Rio of monocropping was described. The saccharinity of lower internodes was higher than that of upper internodes, the upper in position, the lower in sugar, at heading. The upper-middle internodes contented more sugar than lower internodes at maturity .The saccharinity of the 5th - 7th internodes (from top to bottom, the following are same) in the upper position of a plant was the highest, and the saccharinity of 1- 2 internodes at the bottom was the lowest (see Fig. 2.10 in 2.2).

As for one internode only, its saccharinity was different between 20 days before heading and 20 days after heading. The saccharinity of each internode were upper > middle > lower of it and the mean of three parts was close to the saccharinity in middle part the 20 days before. But the 20 days after the saccharinity of the 7th internode and those below the 7th were the same as the 20 days before .The internodes above the 7th had an opposite order of saccharinity, lower > middle > upper .In addition no matter when these were measured, early or late, the saccharinity of upper part and lower part within an upper internode were greatly different but those within a lower internode were a little different.

The saccharinity of different parts of each internode showed a tendency to decrease which was the more evident the more close to fully ripe maturity.

The accumulation of dry matter weight of internodes differed from each other in sweet sorghum. The most content of sugar was the 11th one in middle-lower position and turned to reduction upward and downward little by little .But the sugar at the bottom internodes was higher than that at the top (also see Fig.2.10). As the dry matter weight accumulation of every internode was different the percentage of the sugar content of each one to the sugar content of whole stalk was not same as well, the sugar content and the dry matter weight of each one were identical, the sugar content of an internode that had heavy weight was also high, and therefore the saccharinity among internodes were contrary to the distribution of sugar contents within internodes. The sugar contents of internodes was higher in middle-lower position than in middle-upper position, and was the highest at the 11th internode. From the 11th on three internodes were added upward and downward respectively (i.e. the 8th to 11 th).They (7 ones) accounted for 62.1% of sugar content of whole stalk and for 62.8% of dry matter weight of whole stalk, but only for 46.7% of all internodes, what is more, the sugar contents of the 1st, 2nd and 3rd of the bottom were 4.6%, 7.6% and 9.0% and the dry matter weight were 5.0%, 8.2% and 10% respectively. That is why the cutting position at harvest should be lowered as far as possible so as to reduce some losses of sugar content of the lower.

Fig. 2.15 The changes of saccharinity within each internode at different stages (Rio)

1 is heading stage	2, 3, 4 and 5	are 10, 20, 30 and 40 days after heading
- - -Upper	- Middle	-.-Lower

(3) Effects of monocropping and intercropping on yield

The result of September 22nd showed that the stalk dry matter weight of 2: 2 intercropping was heavier than that of monocropping, 14694. 65kg/ha and 11451.96 kg/ha respectively, and increased by 28%. The dry matter weight of panicle was measured on October 3rd. The dry matter weights of 2: 2 intercropping and monocropping were 5384.39 kg/ha and 4750.2 kg/ha, and increased by 13%. The grain yield of 2: 2 intercropping, 4105.2 kg/ha, was 7.9% more than that of monocropping, 3802.5kg/ha. The former was slightly higher than the latter in biomass.

The fresh weight of 2:1 intercropping of Shennong No.2 and pea was 9% more than that of monocropping. The biomass of the former was 10% more than that of the latter. The economic yield of the former, 5079.75 kg/ha, was 20% more than that of the latter, 4035.0 kg/ha. Furthermore the price of pea is higher, so the economic effect can be increased by use of intercropping.

b) Plastic mulch and control

(1) The effect of plastic mulch on plant development

The treatment of plastic mulch was of fast emergence and early maturity. The stages of emergence and heading were 10-17 days earlier than those of control. On September 27th the former had ripened safely but the latter was still at milk stage.

The result of July 30th indicated that in plastic mulch the plant eight was above 100cm, the stalk thickness was 1.6cm, the number of leaves was 2.5 blades more than that of control and the plants had begun to elongate. But in control the plant height was below 50cm and the stalk thickness was not more than 0.5 cm. According to the observations of elongation, flag leaf, heading and maturity, the development courses of plastic mulch are all faster than those of control, especially the promotion role in early development was more clear.

Because of promoting plant growth by plastic mulch, the leaf area stretched faster and the leaf area index went up rapidly during elongation and heading which exceeded the control obviously. The leaf area index (LAI) maximum was higher than in control and lasted over 10 days longer (Table 2.14). The leaf area duration (LAD) of it was stronger.

For example From July 1st to July 17th that of plastic mulch was 306015.0 m₂*day /ha and that of control was 202309.5 m₂*day/ha. From August 4th to August 17th the former was about 80% higher than the latter.

Table 2.14 Effect of plastic mulch on LAI

Treatment	Jun.30	Jul.17	Aug.3	Aug. 17	Aug.29	Sep.7
Plastic mulch	1.3	3.1	4.2	3.7	3.6	3.4
Control	0.12	2.0	3.1	3.4	3.7	3.2

Since the development course of plastic mulch sped up and photosynthate was made more greatly for the stronger LAD, the observed dry matter weights of leaf, sheath, stalk and panicle were all higher than those of control at all kinds of development stages. The accumulation of dry matter per hectare was also high .In plastic mulch the accumulation was 2100kg of June 30th, 8325kg of August 3rd and 19845kg of September 27th but in control the corresponding values were 34.5, 5107.5 and 18007.5 .It was more clear that plastic mulch promoted early development. Not only the stalk dry matter weight but also the stalk saccharinity of plastic mulch were higher than those of control. The sugar contents of all the internodes were higher. The saccharinity of each internode except two ones of top and bottom got to 17- 18% but most of internodes of control were below 17%.

(2) Effect of plastic mulch on yield

From Table 2.15 the fresh weight and the dry matter weight per hectare in plastic mulch were higher distinctly than those in control .The yield of fresh stalk per hectare of September 27th was 65737.5 kg which was 10.6% higher than that of control, 59422.5kg. The grain yield, 3052.5kg, was above 30% higher than that of control, 2242.5kg. As to biomass the former, 19845kg, was 10.2% higher than that of the latter, 18007.5 kg. In plastic mulch the heading was early and the milk time was long and the 1000- kernel weight was 21.4g. But in control that was 15. 4g and the grains were light and blighted and could even not ripen normally before frost .

Table 2.15 Effect of plastic mulch on yield

Treatment		Plastic mulch	Control
Freshweight (g/plant)	Stalk	913.06	808.48
	Panicle	72.56	69.48
Dryweight (g/plant)	Stalk	275.60	245.08
	Panicle	45.84	39.10
Dryweight of panicle (g/panicle)		45.84	40.89
Grain dryweight (g/panicle)		40.95	32.10
Grain number/panical		1980	1980
1000-kernel weight (g)		21.40	15.40
Yield of grain (Kg/ha)		3052.50	2242.50
Biomass (Kg/ha)		19845.00	18007.50

c) Effects of leaf-cutting and head -cutting on saccharinity and dry matter weight of stalk

All leaves or full heads of plants were cut out 30 days after heading and 10 days later the measurement showed that the saccharinity of all stalks reduced after leaf-cutting, which was even from top to bottom .After head-cutting the saccharinity of stalks did not change greatly and the saccharinity of 3-5 internodes of upper only increased slightly .The dry matter weight of stalk of leaf- cutting was clearly lower than that of its control but that of whole stalk of head-cutting was not different from its control (Table 2. 16) . These showed that the photosynthate of leaves was mainly for the accumulation of solvable sugar and dry matter of stalk 30 days after heading . At the same time the accumulation of dry matter weight of panicle had reduced obviously. So head-cutting did not affect the increases of sugar and dry matter yield of stalk enormously. If the yields of sugar and stalk want to be increased by use of head- cutting, the time of treatment should be moved up. The Japanese scientist, Hoshikawa K., cut head at heading and made dry weight and saccharinity of stalk increase significantly.

Table 2.16. Effect of leaf-cutting and head-cutting on dry matter weight and saccharinity of stalk

Item Treatment	Dryweight of stalk (g/plant)			Saccharinity (%)
	CK	Leaf-cutting	Head-cutting	CK	Leaf-cutting	Head-cutting
Internode of panicle	6.5	5.5	6.0	17.3	15.7	15.9
Internode 2	4.8	3.9	4.7	17.1	16.3	17.5
3	5.6	4.3	5.1	16.8	15.6	17.7
4	7.1	5.2	6.5	17.3	15.5	17.6
5	8.8	6.5	8.4	17.6	16.4	17.2
6	10.2	7.8	9.5	18.0	16.7	17.0
7	11.5	8.8	10.6	18.2	16.8	17.9
8	12.6	9.6	12.0	17.8	16.5	17.3
9	15.4	12.2	14.3	17.5	16.7	17.9
10	17.8	15.4	19.7	18.2	16.5	16.9
11	20.2	20.2	22.0	17.3	16.1	16.6
12	21.1	18.5	20.9	16.8	15.8	16.8
13	17.7	14.9	19.2	17.4	15.8	17.1
14	14.9	14.0	16.3	17.2	15.2	16.5
15	11.4	10.7	14.5	15.5	15.0	16.1

2.6.4 conclusions

a) The intercropping of sweet sorghum and sweet potato with short stalk, or and pea with short duration could promote the accumulations of dry matter and sugar of stalk. Both intercropping and monocropping had sugar growth curves of two-peak shape similarly. But the peak had higher values and appeared earlier and the accumulated rate of dry matter was also faster in intercropping. Therefore the economic yield and biomass could be increased by using the intercropping of sweet sorghum.

b) The use of plastic mulch cultivation of sweet sorghum could speed up the development course. Leaf area stretched faster and leaf area index was higher, which lasted longer .The heading or maturity was about 10 days earlier than that of control and the accumulation of dry matter weight and sugar of stalk could be increased. Meanwhile grains were plump and 1000-kernel weight was high. Therefore biomass not only was increased but also economic yield greatly increased.

c) Under the condition of monocropping after heading was an important stage of the production of sugar and dry matter of stalk in sweet sorghum. The accumulation of sugar was the fastest 10- 20 days after heading and reached the highest when grains were ripe.

d) All the leaves of plants were cut out 30 days after heading, which reduced the saccharinity of stalk and had the dry weight lower than that of its control clearly .The full heads of plants were cut out in the mean time, which did not affect the saccharinity and dry matter clearly.

References

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2. Hoshikawa, K., 1981, Pre-experiment of cultivation of biological energy sweet sorghum, Agriculture and horticulture, No.4, Vol.56, 497-503.

3. Karve, A.D., Ghaneker, A.R. and Kshirsagar, S.H., 1975, Further investigations on sweet sorghum, Sorgum Newsl. 18: 40-1.

4. Li Huaibin et aL, 1984, Accumulation and distribution of dry matter and formation of grain yield in sorghum at the level of 500 Kg/mu, Acta Agronomica Sinica, Vol.10, No.2, 87-94

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