Productivity of the white clover

Toomas Laidna

Institute of Grassland Science and Botany, Estonian Agricultural University
Lai str. 34, EE2400 Tartu, Estonia

Introduction
Material and methods
Results
Discussion and conclusions

Introduction

Among the perennial legumes of Estonia only white clover and sickle medic (Medicago falcata) are suitable for the pastures. The breeding of white clover varieties began in Estonia more than 60 years ago; the variety Jõgeva 4, developed in Jõgeva Plant Breeding Station at that time, has been in use since. In 1979 a field experiment was established at the Grassland Experimental Station of the Estonian Agricultural Academy, where Jõgeva 4 was studied along with the other forage leguminous species (Trifolium pratense, T. hybridum, Galega orientalis, Medicago media, M. falcata). The general purpose of the experiment was to study the effect of two different N sources (grass + mineral N, 100-400 kg ha^-1 and grass/legume mixtures) on the productivity of the sward, and on the accumulation of organic matter (OM) and N in the soil. This paper deals with the grass/white clover sward.

Material and methods

The grasses (Festuca pratensis, Phleum pratense, Poa pratensis, Lolium perenne) were sown together on the experimental field at the beginning of August 1978 (altogether 21.9 kg ha^-1 of seed with 100% seeding value). The white clover was sown additionally in April 1979 (6.0 kg ha^-1 with 100% seeding value). Every year the experimental field was fertilized with 30 and 70 kg ha^-1 of P and K, respectively. No fertilizer N was given to grass/white clover mixture. Harvesting was done by mowing four times during each growing season. The root mass was examined by taking soil-root monoliths (0.15 × 0.15 × 0.20 metres) in August every year. Soil samples were taken every year at the beginning of October (after the last harvest) to determine the agrochemical parameters of the soil. The experimental field was on pseudopodzolic soil where the agrochemical parameters of the ploughed layer (0-20 cm) were favourable for sward growth: OM, 2.15%; total N, 0.125%; lactate-soluble P, 85 and K, 110 mg kg^-1; pH_KCl was 5.5.

The plot size was 7.15 × 1.4 m, and there were four replications. The herbage yield was measured by cutting with a frontal fingerbar mower MF-70 leaving a 5 cm stubble height. Components of green mass yield were determined by hand separation. The ordinary chemical characteristics of herbage (including amino acid composition in its protein) was determined. During the experimental period (1979-1990) the average precipitation (from April to October) was 452 mm; additional water (mean of 57 mm) was given each year by sprinkler irrigation of the experimental plots.

Results

Although the spring of 1979 was poor in precipitation (April, 16.8, May, 45.5 and June, 17.0 mm) the white clover introduced into the grass sward was present (47.5%) by the 2nd cut, due to the irrigation (6 times during the season and amounting to 185 mm). The average proportion of the white clover in the yield of 1979 was 35%.

During the next four years the proportion of the white clover remained between 47-73%; only from the 6th harvest year did its proportion decrease somewhat (at the same time the proportion of the forbs increased noticeably), and by the last year of the experiment (1990) its share in the sward was still 47.3% (grasses, 26 and forbs, 27%, respectively). Thus under the conditions of frequent cutting and irrigation, the contribution of Jõgeva 4 remained fairly constant for a relatively long period (12 years). Herbage yield data, given in Table 1, show that the productivity of the mixed sward was relatively stable throughout the years - up to 57.00 t ha^-1 green matter, 9.90 t ha^-1 DM, and 1.79 t ha^-1 crude protein. A significant decrease in productivity only took place from the 10th harvest year onwards.

Table 1. The productivity of the mixture grass/white clover (t ha^-1)

	Years of experiment			Average 1979-90
	1979-84	1985-87	1988-90
Green matter	52.4	42.8	28.1	44.0
Dry matter	8.20	7.90	6.70	7.50
Crude protein (kg/ha)	1.49	1.30	0.96	1.26

Table 2. Chemical composition (% in DM) of grass/clover herbage

Parameter	Year of experiment							Average 1979-85
	1979	1980	1981	1982	1983	1984	1985
Crude protein	16.3	20.2	19.3	19.7	16.3	17.8	15.4	17.9
Crude fibre	21.9	21.3	20.2	21.5	23.0	22.4	22.8	21.9
Crude fat	2.79	3.47	2.98	2.90	2.72	3.49	3.49	3.12
Crude ash	10.9	11.9	10.7	10.2	9.9	10.6	10.8	10.7
N-free extracts	48.1	43.1	46.8	45.7	48.1	45.7	47.5	46.4

Table 3. The amino acid composition of the herbage DM

Year	Essential amino acids g kg-1						Sum of other AA, g kg-1	Total AA g kg-1	Total AA in CP (%)
	Thr Val	Met Isl	Leu Phe	His Arg	Lys	Total
1979	5.25 6.67	1.92 5.33	9.45 6.35	6.64 7.72	8.20	57.62	61.42	119.04	73.0
1981	6.72 8.90	2.01 6.87	11.73 5.54	5.71 9.19	9.81	66.48	78.25	144.73	75.0
1983	6.33 8.40	1.83 6.31	9.97 6.10	7.98 7.78?	9.27	63.97	76.54	140.51	86.2
1985	6.04 7.19	1.50 5.17	9.04 6.54	4.62 6.42	7.60	54.12	71.90	126.02	81.8
Average	6.09 7.81	1.82 5.92	10.05 6.13	6.24 7.78	8.72	60.55	72.03	132.58	79.0

Table 4. Root DM yield (t ha^-1) distribution in uppersoil layers, herbage DM yield (t ha^-1) and ratio of herbage to root yield (%)

Year of experiment	Soil layers (cm)				Herbage yield t ha-1	Ratio of herbage to root yield (%)
	0-5	5-10	10-20	0-20		Herbage	Roots
1979	1.30	0.21	0.13	1.64	8.40	83.7	16.3
1981	1.02	0.08	0.07	2.52	7.90	87.1	12.9
1983	4.52	0.71	0.64	5.87	8.70	59.7	40.3
1985	6.14	0.94	0.85	7.93	9.90	55.5	44.5

One of the most important parameters for determining the yield quality is the content of crude protein (CP). The main factors influencing CP content are the species of plant and the stage of development of the plant when cut (Frame 1992). During the course of the present experiment CP content was always above the desired value for dairy cows (14% in DM) and over the experimental period averaged 17.9%. The content of crude fibre, crude fat and crude ash were all in accordance with the optimum values necessary for ensuring the high productivity of dairy cattle. Average values over seven years were: of crude fibre, 21.9% (optimum 14-26%; Oil, 1982): crude fat, 3.12% and crude ash (i.e. mineral compounds), 10.7%. In more detailed studies, the amino acid composition of the DM was determined (Table 3); 17 amino acids were found, including all the essential ones. During the first harvest years the herbage DM yield (Table 4) was relatively stable (about 10 t ha^-1) and its share in the total phytomass (yield + roots) was up to 87%. Only from 4th or 5th harvest year there was a marked increase in the mass of the roots, and therefore the ratio between the roots and yield became narrower. The influence of the clover-rich sward on the soil, in terms of contents of OM, N and other nutrient elements, is given in Table 5. The data indicate that during the 7 years, content of OM (humus) increased by 30%, but the bulk density and contents of mineral nutrients decreased.

Table 5. The influence of the grass/white clover sward on agrochemical parameters of the soil

Time	OM (%)	Total N (%)	Bulk density g cm-3	pHKCl	Available nutrient elements, mg kg-1
					P	K	Ca	M
1979	1.91	0.134	1.47	5.49	150	170	1000	70
1985	2.21	0.131	1.37	5.59	70	50	1050	60

Discussion and conclusions

The results of the research showed that the method used in our experiment, namely, grasses sown at the end of July or the beginning of August, and the legume sown additionally the following spring, is fully justified for the establishment of a new sward. The sward was fully developed by the autumn of the year of sowing the white clover. The proportion of white clover in the herbage yield remained relatively constant during the first 9 years; only from the 10th year was these a noticeable decrease in its contribution. The existence of a high and stable white clover component in the sward fully met the nutritional needs of dairy cattle. Also, under a grass/white clover sward the supply of OM in the soil are replenished.

REFERENCES

Frame, J. (1992). Improved Grassland Management. Farming Press, Ipswich, p. 148.

Oil, Ü. (1982). Põllumajandusloomade söötmise ABC. Tallinn, Estonia, p. 334.