Argaadi Parol
Institute of Grassland Science and Botany, Estonian Agricultural University
Lai str. 34, EE2400 Tartu, Estonia
Introduction
Materials and methods
Results
Discussion and conclusions
References
The importance of white clover in pastures utilized intensively, depending on soil and weather conditions, was investigated. Pastures rich in white clover were established both as temporary and permanent (long-term) swards. On temporary pastures in Estonia clovers and tall grasses are the dominant species (Sau, 1977). For permanent pastures a type of the sward sown with low grasses and white clover can be recommended (Sau, 1977; Parol, 1986). The clovers are essential to enhance the quality of the pasture herbage. The estimation of the pasture composition is essential at the establishment of a highly productive sward which it is envisaged will produce the maximum amount of milk per unit of pasture area. The most valuable and persistent swards are those pasture swards which include 15 to 35% of white clover (Adojaan, 1955). Results are presented to show the effect of white clover on the milk production of dairy cows.
The trial was carried out on the experimental farm of Sootaga (20 km from Tartu) during 1975-82. Experimental paddocks with a size of 0.14-0.36 ha were established on a gleyed sodpodzolic soil with mean pH 5.3, a humus content of 2.55%, lactate-extractable P - 45 mg kg-1 and K - 115 mg kg-1. The grassland was divided into two parts: a temporary swards with an arithmetical mean age of 3 years (maximum 5 years) and long-term swards with an arithmetical mean age of 9 years. Each type of sward was grazed by a separate group of cattle each of 8 cows. The seed mixture sown (kg ha-1) was: white clover, 6.8; red clover, 3.4; timothy, 4.5; meadow fescue, 11.1; meadow foxtail, 1.6; perennial ryegrass, 5.0 and smooth-stalked meadow grass, 5.1.
Equal amounts of phosphorus (superphosphate) and potassium (potassium chloride) fertilizers were applied to both type of pastures, namely P at 40 and K at 75 kg ha-1. Nitrogen fertilizer (ammonium nitrate) were given in one or two dressings in spring or summer depending on the content of clovers. The mean rates of fertilizer N were: 50 kg ha-1 on the temporary sward and 68 kg ha-1 on the permanent one.
The trial paddocks were grazed separately with a stocking rate of 2.3-3.1 cows ha-1 (May-September). To clarify the effect of clovers on milk production, the experimental years were divided into two groups with regard to the distribution of white clover in the sward. In the years when there were unfavourable conditions for white clover the proportion of clovers in temporary swards was 19-29% and in favourable years, 32-36%; on permanent pastures the contribution of white clover was 8-10% and 11-18%, respectively. Red clover sown had an impact mainly in the first 2 harvest years after establishment of the sward. To determine the productivity of a pasture the dairy cows were weighed at the beginning and at the end of the grazing period and also after each grazing cycle. To evaluate the milk production, the yield of milk produced by each cattle group was weighed after every milking.
The biological accumulation of nitrogen by clovers has a favourable effect on the milk production of cows. The difference in milk production per hectare due to a higher contribution of clovers in the swards (Table 1) was an increase on the both temporary and permanent grasses/clover swards of 10%. The absolute increase in yield of milk ranged from 453 to 463 kg ha-1.
If it is considered that the proportion of clovers in the temporary sward in the years favourable for legumes was on average 35%, and in the unfavourable years, 23%, then an increase in milk yield per 12% difference of the clover content was 453 kg, or 38 kg ha-1 per 1% of the clover proportion. Thus, though there was a significantly higher content of clover in the temporary swards, this was not clearly reflected in higher milk yields. In fact, much higher milk yields per 1% of the clover content was provided by the permanent swards.
Table 1. The dependence of milk productivity on the proportion of clovers in grass clover pastures (May-September, 1975-82)
|
Content of clovers (%) |
Milk production |
|||
|
kg ha-1 |
Increase in yield |
|||
|
kg ha-1 |
% |
|||
|
Temporary sward: |
|
|||
|
|
19-29 |
4179 |
|
|
|
|
32-36 |
4632 |
453 |
9.8 |
|
Permanent sward: |
|
|||
|
|
8-10 |
3931 |
|
|
|
|
11-18 |
4349 |
463 |
10.5 |
In the first harvest years the temporary sward included a great number of other valuable grass species, e.g. perennial ryegrass, timothy and meadow fescue.
Apart from the importance of white clover to milk production it also had an effect on the live weight gain of cows. In the temporary sward with a high content of clovers, annual live weight gain was 106 kg ha-1. In the same sward, but in the years unfavourable for the growth of clovers an increase in the weight of cows was 128 kg ha-1. In some years (1977, 1978, 1980) there was a loss in the live weight of dairy cows during the last grazing cycle in autumn. The contribution of white clover in the herbage yield increased from 10-26% in the spring up to 35-43% in the autumn. Under these conditions the cows had a live weight loss of 29 to 52 kg ha-1
In the permanent sward the content of white clover did not change as much as that in the temporary sward but it still had a significant effect on the increase in live weight.
A decrease in live weight of cattle is not directly connected with the content of white clover in the sward, but indirectly due to the effect of white clover on the milk production of cows. As the yield of milk increases the animals' weight can be reduced. To estimate milk production and changes in cows' live weight together from both type of pasture with regard to the influence of white clover they are expressed in units of energy (Table 2).
Table 2. Energy production from the pastures
|
Content of clovers (%) |
Energy production |
|||
|
MJ ha-1 |
Increase in yield |
|||
|
MJ ha-1 |
% |
|||
|
Temporary sward: |
|
|||
|
|
19-29 |
15424 |
|
|
|
|
32-36 |
15968 |
544 |
3.5 |
|
Permanent sward: |
|
|||
|
|
8-10 |
13722 |
|
|
|
|
11-18 |
15173 |
1451 |
10.6 |
It was calculated by this way (Oil et al., 1972), that 1 kg of milk with a fat content of 4% corresponded to 0.75 Meal (3.14 MJ) and an increase of 1 kg in live weight, 3.2 Meal (13.4 MJ). By creating the favourable conditions for promoting clovers (intensive grazing, moderate nitrogen fertilization) it is possible to increase the energy production by 3 to 10%, especially when the pasture has a low species diversity.
In the short-term sward with a high content of clovers (19-36%) a change in the amount of clover had a smaller positive effect on the productivity, measured as feed units (FU), of the sward (2.5%) compared with that of the permanent sward (5.7%), where the content of white clover was only 8-18% (Table 3). To determine the productivity of pasture in feed units, the calculations considered the maintenance requirements for cows as well as milk production and live weight gains.
Table 3. Pasture productivity evaluated for dairy cows and an importance of clover in a grass/clover sward
|
Content of clovers (%) |
Pasture production |
|||
|
Feed units per ha* |
Increase in yield |
|||
|
Feed units per ha |
% |
|||
|
Temporary sward: |
|
|||
|
|
19-29 |
4104 |
|
|
|
|
32-36 |
4209 |
105 |
2.5 |
|
Permanent sward: |
|
|||
|
|
8-10 |
3705 |
|
|
|
|
11-18 |
3918 |
213 |
5.7 |
* 1 FU = 1 kg oats
White clover is especially valuable for dairy cows, because they need a high-yielding, high-protein and nutritious forage crop. It plays a significant role in seed mixtures for grazing. The trial indicated that the presence of white clover in pastures was favourable for the milk yield of dairy cows. Under the Estonian agroclimatic conditions, where the first period of summer is dry and the second is usually wet, white clover spreads rapidly after midsummer. In that period milk production usually begins to decline. By increasing the distribution of white clover within pastures we can reduce the lowering of milk yield at this time. White clover is particularly essential in the permanent pasture swards, where it may increase the milk production per hectare relatively much more (per 1% of the clover content) than in the case of temporary pastures.
Adojaan, A. (1955). Kultuurkarjamaade tähtsamad heintaimed ja kõrgesaagiliste rohukamarate kujunemine. Kultuurkarjamaade rajamine ja kasutamine. Tallinn, Estonia, pp. 78-106.
Oll, Ü., Older, H., Kree, A. (1972). Eri rohukamarate toodanguvõime katsekultuurkarjamaadel Sootaga sovhoosis. - Sotsialistlik Põllumajandus, No. 12, pp. 536-538.
Parol, A. (1986). The productivity of cultivated pastures evaluated by dairy cows depending on the botanical composition and fertilization. Bioproduction of grasslands. Tallinn, Estonia, pp. 141-148.
Sau, A. (1977). Intensiivkultuurrohumaade tüübid - Teaduse saavutusi ja eesindlikke kogemusi põllumajanduses. Tallinn, Estonia, No. 30, pp. 8-13.
