Jonas Slepetys
Lithuanian Institute of Agriculture
5051, Dotnuva-Akademija, Kedainiai distr., Lithuania
Introduction
Materials and methods
Results and discussion
Conclusions
References
When large plots of white clover are grown for seed it is important to know the earliest time of harvesting and its duration. White clover can flower over a long period, especially when summers are wet. Seed harvesting begins when it is expected to achieve the highest yield of mature seeds (Grigas, 1976; Radej, 1983). Many researchers recommend determining harvest time for clover seed according to the amount of mature heads (Vlcan, 1987; Liaukonis, 1988). In western Europe a calendar method is used for the determination of white clover harvesting time, counting the days from full flowering till harvesting (Cedell, 1974; Jensen, 1985). However, this method of determining the time of maturity is only approximate.
White clover seed maturity has not been studied in Lithuania. The aims of the trials reported here were: a) to study seed maturity dynamics, b) to find a simple method to determine harvesting time, c) to identify an optimum harvesting time of white clover, using desiccation and, d) to study the changes in the quality of seed stored for several years.
Experiments were carried out between 1982 and 1995. The mean yearly temperature was 6°C and annual precipitation, 572 mm. The growing season ranged from 169 to 202 days. Climatically Lithuania belongs to the west European Atlantic - continental area. The site of the trials was 75 m. a. s. 1. The soil was a drained sodic gley, light loam. The arable layer was 0.22-0.25 m with a pH 7.1-7.3. The content of available P2O5 and.K2O was 170-188 and 129-156 g per kg soil, respectively, and the content of total N 0.14-0.16%, and of humus 1.91-2.22%.
During 1982-1985, the seed maturity dynamics of white clover cv. Bitunai were measured 4-6 weeks from the beginning of flowering and at weekly intervals for 2-3 months on 1 m2 plots. Every week "Region" was applied to white clover and after 3-7 days, the material was threshed in a laboratory thresher. Betwen 1986 and 1987 the yield was harvested with a "Sampo - 500" combine. Each time, before desiccation, 3-4 samples from 0.25 m2 plot were taken for the maturity estimation of the sward. White clover heads were separated from stems and, without flowers and buttons, were divided into three groups: 1. Mature, i.e. calyxes were browned, seed hard. 2. Semi-mature with grey calyxes and seeds in waxy ripeness. 3. Immature with green calyxes.
Over 1986-1995 different harvest times and changes in the quality of the seed yield were investigated, with seed being stored in a dry, warm place in paper bags.
White clover heads which flower early are the most productive. It is possible to obtain seed which matches up to quality standards only from heads which flowered no later than the first ten-day period of August. Seed obtained from heads which began to flower at the end of August had a 1000-seed weight of 0.39-0.45 g and a germination of 51-57%. The main part of the seed yield was obtained from heads which flowered in June and the first half of July.
For the seed maturation of entirely distinct heads an active temperature total of 501±19°C, and an effective total temperature of 186±13°C, is necessary (counting from the start of the flowering stage). One of the reasons why seed from later flowering heads does not ripen fully is the lack of effective heat.
Seeds obtained from desiccated semi-mature heads did not differ in quality from seeds of completely mature heads. Seeds from immature and semi-mature heads, desiccated or ripened in a swath did not differ much in quality (Table 1).
Table 1. White clover seed quality of different maturation and harvested by different methods (Mean of 1982-1987)
|
Harvesting method of heads |
Immature heads |
Semi-mature heads |
||||
|
green calyxes, light brown petals |
grey-yellow calyxes, dark brown petals |
grey calyxes, dark brown petals |
||||
|
1000-seed mass, g |
germination, % |
1000-seed mass, g |
germination, % |
1000-seed mass, g |
germination, % |
|
|
Not desiccated |
0.45 |
66 |
0.62 |
79 |
0.63 |
81 |
|
Desiccated |
0.32 |
36 |
0.50 |
66 |
0.63 |
80 |
|
Matured in a swath |
0.37 |
43 |
0.53 |
71 |
0.66 |
78 |
|
LSD05 |
0.16 |
14.2 |
0.06 |
9.1 |
0.05 |
12.4 |
The earliest possible desiccation time was determined taking into account the following conditions: 1) seed yield during harvesting time must be the highest or increasing within the limits of standard deviation, 2) seed germination must meet the quality standards. If seed germination at all harvesting dates is lower, the earliest possible harvesting time is determined according to the yield of germinable seed. Generalized indices for the determination of earliest possible desiccation time are provided in Table 2. Seed yield in all the years is given in g m-2
The earliest white clover desiccation time can be better established according to the abundance of mature (calyxes and petals brown) and semi-mature (petals brown, calyxes grey, pod stalks yellowish green) heads than only according to mature heads. Temperature sum from the start of flowering was a more accurate index for the establisment of desiccation time than the number of days.
The earliest white clover desiccation time occurs when completely mature heads make up 54 ±2.4%, and mature and semi-mature heads make up 67±1.0%. A tentative desiccation time is eight weeks from the beginning of flowering when the sum of active temperatures reaches 885°C. The average optimum harvesting duration is 2 weeks (8-10 weeks from the beginning of flowering). It is most important to establish the earliest possible desiccation time, since knowing the optimum harvesting duration it is possible to adjust to changeable weather. Furthermore, when mature heads bend down to the ground the losses increase due to unharvested heads.
Table 2. Mean data for the earliest possible desiccation time of white clover seed crops
|
Year |
Sum of days from start of flowering |
Sum of Ts from start of flowering(°C) |
Mature heads, % |
Mature and semi-mature heads, % |
Seed germination, % |
1000 seed mass, g |
Seed yield g m-2 |
Harvest time, weeks from start of flowering |
|
1982 |
49 |
740 |
58 |
64 |
87 |
0.58 |
28 |
7-10 |
|
1983 |
63 |
1019 |
44 |
66 |
84 |
0.70 |
12 |
9-10 |
|
1984 |
63 |
942 |
60 |
67 |
70 |
0.74 |
14 |
9-11 |
|
1985 |
49 |
789 |
50 |
70 |
70 |
0.66 |
20 |
7-9 |
|
1986 |
48 |
838 |
55 |
64 |
83 |
0.75 |
47 |
7-9 |
|
1987 |
64 |
984 |
57 |
69 |
81 |
0.76 |
11 |
9-10 |
|
Mean |
56 |
885 |
54 |
67 |
79 |
0.70 |
22 |
8-10 |
|
Standard deviation |
±3.3 |
±46 |
±2.4 |
±10 |
|
|
|
|
|
Variation |
14.4 |
12.6 |
11.0 |
3.8 |
|
|
|
|
Variation in the seed quality of the seed differing in maturity harvested in 1986 with a combine was investigated up to 1995. The seed was stored for up to nine years (seed moisture content, 8.1-9.0%). After three years of seed storage the germination was similar to that at the start of the experiment and met the quality standard requirements (Table 3).
Table 3. Variation of white clover seed germination % harvested in 1986 and stored over nine years
|
Desiccation and harvest date |
Year |
||||||||
|
1986 |
1988 |
1989 |
1990 |
1991 |
1992 |
1993 |
1994 |
1995 |
|
|
22-28/7 |
89.5 |
81.8 |
89.0 |
72.5 |
72.5 |
75.5 |
64.0 |
59.3 |
48.5 |
|
30/7-4/8 |
83.5 |
85.2 |
88.3 |
62.2 |
59.7 |
62.7 |
57.5" |
62.8 |
49.5 |
|
4-8/8 |
86.0 |
87.0 |
88.0 |
67.0 |
64.2 |
73.5 |
61.3 |
65.0 |
47.5 |
|
6-8/8 |
88.7 |
84.5 |
88.8 |
63.2 |
61.0 |
63.7 |
60.3 |
54.0 |
50.0 |
|
13-15/8 |
86.2 |
88.2 |
90.3 |
70.5 |
61.2 |
58.7 |
60.0 |
65.5 |
54.8 |
|
15-8 Nx |
85.0 |
86.0 |
90.8 |
62.7 |
59.7 |
53.5 |
57.5 |
54.5 |
43.5 |
|
LSD05 |
5.5 |
6.0 |
7.1 |
6.2 |
5.6 |
5.6 |
9.9 |
6.2 |
5.6 |
Nx - not desiccated
In the fourth year of the seed storage the germinating capacity decreased markedly and was equal to 62.2-72.5%. When the seed was stored for a longer period the germination regularly decreased. The seed which was not desiccated stored worse than desiccated seed. The quantity of hard seed decreased from 26.3-30.4% to 18.0-24.8%. Seed vigour after 9 years was low, 13.0-18.5%, a reduction by 2.8 times.
White clover desiccation time can be more accurately established according to the number of completely mature heads (calyxes and pod stems brown) and semi-mature heads (calyxes grey, pod stems yellowish green) than using only the number of mature heads.
The earliest time for white clover desiccation ocurs when the amount of mature and semi-mature heads in the stand makes up 65-70%.
The sum of temperatures from the beginning of stand flowering was a more accurate index for the establishment of the earliest desiccation time than the number of days. The earliest white clover desiccation time is when the accumulated sum active temperatures reaches 885°C from the beginning of flowering.
A tentative optimum white clover harvesting time is 8-10 weeks from the beginning of flowering.
When the whole area of white clover is harvested over one week and head maturity analysis is not made due to whatever reason, it is best to desiccate in the 9th week from the beginning of flowering. The start of flowering is marked when 10% of the buttons start flowering.
Germination of stored seed decreased noticeably in the fourth storage year. Undesiccated seed performed worse than desiccated seed.
CEDELL, T. (1974) Kloverfröskord. Svensk Frötidning. 43, No 718, pp. 89-93.
GRIGAS, A. (1976) Daugiameciu zoliu seklininkyste. pp. 191-196.
JENSEN, T.F. (1985) Valg af høsttidspunkt for froafgrøder. Dansk Frøavl. 68, No 10, pp. 228-230.
LIAUKONIS, J. (1988) Seklazoliu ir sekloju dorojimas. pp. 61-75.
RADEJ, J. (1983) Pestovani jetele plaziveho na semeno. UVTJZ. Rostlinna vyroba. No 1, pp. 1-54.
VLCAN, M. (1987) Pestovani jetele plaziveho na semeno. Uroda. 35, No 2, pp. 64-65.
