The investigations on white clover in north-west Russia

I. Lepkovitch, Novgorod State Agricultural Academy, St Petersburg, Russia

Introduction
Materials and methods
Results
Discussion

Introduction

White clover is a valuable pasture plant widespread in the native grasslands of north-west Russia. Investigations on white clover were carried out there and also in central Russia (Moscow), Estonia and Belorussia. The problems encountered were: combining biological clover N and fertilizer N, the use of white clover not only on the pastures, but on mown grasslands, and the introduction and sowing of new varieties.

Materials and methods

The investigations were conducted during 1970-90 in the Leningrad district -the centre of north-west Russia. The soils are typically acid dernovo-podsolic, pH 4.8-5.0. The sum of active temperatures (2 10°c) is 1800-2000°. The sum of precipitations during the growing season (May-September) is 350-370 mm. There are deficits of soil moisture in May and June and a drought in May some years. Tests were made in pots and in the field. After liming, the pH was 5.5-6.0. The basic fertilizers applied were P and K at moderate annual doses: P₂O₅ (60-70 kg ha^-1) and K₂O (80-90 kg ha^-1). Russian, Belorussian, Estonian and Danish varieties were studied in pure stands and with companion grasses. Swards were grazed or mown three times a year.

Results

In the pot trials white clover plants were grown for 2-3 months after sowing and in the field over a period of 5-7 years. Observations were made on shoots, roots, yielding ability and the chemical composition of the plants. Plant growth speeded up during the first 2.5 week period as a result of N application but not afterwards (Table 1).

Table 1 The effect of fertilizer N on establishing white clover plants in pots (Shoot and root DM per plant)

Date of yield assessment	Control (no N)		17 ppm of N
	g	% on dates	g	% on dates	% to control
cv. Jogeva 4 (Estonia) 1978
4 July	0.006	100	0.014	100	233
22 July	0.209	3,483	0.206	1,471	99
10 August	1.112	18,533	0.546	3,900	49
cv. Pavlovskii (Russia) 1979
2 July	0.016	100	0.018	100	113
20 July	0.180	1,125	0.144	800	80
11 August	1.950	12,188	1.610	8,944	83

A similar test was repeated in 1980 on a Danish variety. The legumes were grown over a 95 day period and when harvested the plants were flowering. The results (Table 2) were similar to those from previous work.

Table 2 Dry matter yield (g) per white clover plant cv. Milka Pajbjerg without and with fertilizer N, 1980

Control (no N)			17 ppm of N
Shoots	Roots	Sum	Shoots	Roots	Sum
18.200	6.000	24.200	17.500	6.000	23.500
100%	100%	100%	96%	100%	97%

In the field experiment pure sown white clover stands had yields equal to those when stands were fertilized with N in spring by 30 to 120 kg ha^-1.

White clover is used as the best pasture legume in mixture with grasses in fanning practice in north-west Russia (white clover is a good plant for honey bees too, flowering as it does from June till September). White clover contribution to yield was 109-15% in May, 309-50% in June-July and increasing to 70-90% in August-September. However, these proportions maybe less in a dry summer or more in a wet season. In the latter, the fertilizer N equivalent of white clover was 120-150 kg ha^-1 but in dry years only 20-30 kg ha¹. White clover noticeably decreased when fertilizer N was used on the mixed sward and it was found that swards became grass dominant in two years when N-fertilized annually with 90 to 150 kg ha^-1. Competition between white clover plants and grasses took place, even when with lower rates of fertilizer N (Table 3).

Table 3 Yields of DM and CP (t ha^-1) and relativity from a Poa pratensis (cv. Jogeva 1)/Trifolium repens (cv. Jogeva 4) sward (Spring, 1970)

		Nil N		30 kg ha-1 N		60 kg ha-1 N
	Sward Components	Yield	Rel.	Yield	Rel.	Yield	Rel.
DM	Grass	3.52	100	4.47	127	5.71	162
	White clover	2.00	100	1.40	70	0.96	48
	Sum	5.52	100	5.87	106	6.67	163
CP	Grass	0.49	100	0.63	129	0.80	163
	White clover	0.45	100	0.32	71	0.22	50
	Sum	0.94	100	0.95	101	1.02	108

The main effect of N fertilizers was to decrease clover contribution (see also Table 4). The significant index here was the basic one for the white clover plant - shoot mass per m of stolen length, which increased when fertilizer N was used i.e. a positive reaction of white clover to mineral N, but the competition from grasses adversely affected white clover growth, as shown in Table 5.

Table 4 Characteristics of white clover cv. Jogeva 4 and Poa pratensis cv. Jogeva 1 in pasture, 1980 (per Shoot, per Leaf)

	68 kg ha-1 N
	Control (No N)		Spring		Summer		Late summer
	g	Rel.	g	Rel.	g	Rel.	g	Rel.
Poa pratensis Shoot (g)	0.022	100	0.025	113	0.025	113	0.027	122
Shoot's base (0-3 cm)(g)	0.006	100	0.009	150	0.009	150	0.008	133
White clover: Leaf mass (g)	0.020	100	0.016	80	0.015	75	0.016	80
Stolon length (m per m2)	102.5	100	47.2	46	57.4	56	86.0	84
Sum of leaf & stolon (g m2)	58.5	100	33.3	57	42.2	72	64.4	110
Shoot (g m2)	0.57	100	0.71	125	0.73	128	0.74	130

Table 5 Leaf area index (LAI) of components of a mixed stand, 1975-80

	Control No N		68 kg ha-1 N
			Spring		Summer		Late summer
White clover	2.71		2.38		2.69		2.59
Poa pratensis	2.74		3.71		3.42		3.31
Dandelion	0.57		0.48		0.51		0.51
Sum	6.02	100%	6.57	109%	6.62	110%	6.41	106%
Total yield t DM ha-1	5.05	100%	5.39	107%	5.51	109%	5.32	105%
Leaf mass in yield (%)	61.6		64.0		62.8		62.8

Having very fast rates of regrowth, white clover showed a good result when mown. Estonian varieties were used in one mixture (white clover Jogeva 4, Poa pratensis Jogeva 1, Festuca pratensis, Jogeva 47 and Lolium perenne cv. Valinge (Swedish cultivar).

This sward was used over 4 years and mowed 3 times annually. During all these years the average content of white clover in the stand was high at 40-85%. The distribution of total DM yield from the 3 mowings was even: 33.2: 34.7: 32.1% on average (Table 6).

Table 6 Dry matter yield from cut mixed sward (4-year mean)

Nitrogen, (kg 1 ha-1)	DM (t ha-1)	%
No nitrogen	5.56	100
51- in spring	6.49	117
51- after first mowing	6.17	111
51- after second mowing	6.61	119

New varieties of white clover can be especially effective for using in a mowing regime when the plants have bigger leaves, for example, the Belorussian variety Volat. In 1988-89 a pure sown stand of Volat had total yields without fertilizer N of 4.4 t DM ha^-1 in the comparatively dry 1988 and 6.5 t DM ha^-1 in the rather wet 1989. The highest yield was obtained when the rainfall totalled 458 mm (or 3.7 mm per growing day) and the temperature degree sum was 1875°C during the growing season (or 15.1°C per day).

The use of mixed swards has an advantageous economic effect and a high yield energy per unit of energy expenditure (22.9); for comparison, the index for grass swards given 150 kg N ha^-1 was only 4.42 at equivalent yields.

Discussion

Grasses with white clover are the classic grassland stands. In north-west Russia such stands are one of the two main types, the other type being pure sown grasses, mainly used for mowing. Mixed stands yield 5-6 t DM ha^-1 without N fertilization and N fertilizer is not effective on white clover during its establishment. Later, fertilizer N may be used once annually. When there is a deficit of fertilizer N, as at present in Russia, white clover is an independent highly effective source of biological N. Soil pH has to be 5.5-6.0 (by liming) and the basic PK fertilizers are required annually. New varieties of white clover adapted to north-west Russian conditions are required in future, for example, cv. Belgorodski (Leningrad district). Hopwever, to expand white clover use in practice, its seed production also requires expansion.