Antonio González-Rodriguez
Centro de Investigaciones Agrarias Mabegondo (CIAM).
Xunta de Galicia. Apartado 10-15080 La Coruña. Spain
Introduction
Materials and methods
Results
Conclusions
Acknowledgements
References
The high use of fertilizer N on grass pastures is a normal practice for milk production in Europe. Since the imposition of milk quotas all the literature normally agrees that milk production has to be mainly based on grass and forage crops, reducing the dependence on concentrates and N inputs, but that assumption is not really observed in practice. In Spain, Galicia is the main dairy region with small farms and low levels of quota, and using pastures and crops and high levels of concentrates. There is a tendency to increase the use of N and concentrates by leading farmers. However grass/clover swards can be successfully integrated on dairy farms that do not have intensive production, provided management to maintain high clover content and high quality pasture is satisfactory. Acid soils in the region need to be fertilized mainly with lime, phosphate and potash to introduce and maintain clover on pastures (Gonzalez 1991).
Bax and Schils (1993) reported that to reach a quota of 400,000 litres under Scottish conditions, the mixed sward needs 25-33% more concentrate per litre of milk than the N fertilizer grass sward in an intensive system with 2.4 livestock units (LU) per ha. Reducing the stocking rate in both herds to 1.9 LU ha-1 by increasing the area by 25%, the same level of quota was achieved with similar concentrate use. In the Netherlands a grass/clover sward with 70 kg N ha-1, with a high variation in clover content among paddocks, and an area 20% more than a grass sward with 275 kg N ha-1, showed no difference in milk production with the same concentrate use for a quota of 420,000 litres. The objective of the present trial is to asses the potential of white clover in pastures to provide the entire lactation requirements of cows calving between January and March and to establish the level of milk production that can be supported at a low level of concentrate use.
Grassland: The grazing trial was undertaken on a total of 12 ha, 7 ha for grazing and 5 ha for silage, on a perennial ryegrass (cv. Brigantia)/white clover (cv. Grassland Huia) pasture established in autumn 1992.
Treatments:
Group-A:
Grass/clover sward with low N
(20 kg ha-1)
Group B:
Grass/clover sward with 200 kg ha-1 of N
(120 in spring and 80 in autumn)
Animal management: The grazing area was divided into two independent areas of 3.7 ha for group A and of 3.3 ha for group B. Two groups of 15 primiparous Friesian cows with a mean calving date of 26/1/93, were used to rotationally graze each area, divided into 12 paddocks. Concentrate feeding was suppressed 15 days after turn-out to grazing on 5 April, with a total of about 400 kg concentrate per cow. Four grazing rotations were made during the spring and most part of the summer. An unusual wet summer in 1993 allowed cattle grazing during August. All cows were housed only during late summer, September, and fed with silage without concentrates. In autumn, from October to December, both groups of cows made two more rotations, grazing the same areas again and the silage areas. The grassland silage made in spring 1993 from a total of 5 ha was enough to feed cows during September and winter of the same year.
Grazing rotations were flexible trying to maintain the same height of pasture in both treatments at entrance and at exit. from each paddock, cutting for silage if paddocks acumulated excesive height.
Sampling: Pre- and post-grazing herbage samples from both groups in alternate paddocks were taken. Net pasture utilized (= intake) was calculated by difference from the pre- and the preceding post-grazing sample. Cows were milk recorded weekly.
The performance of the swards is summarised on table 1.
Table 1. Performance parameters from the grazed grass/clover sward.
|
Treatments |
Spring |
Autumn |
Total |
||||
|
A |
B |
A |
B |
A |
B |
||
|
N applied (kg ha-1) |
20 |
120 |
0 |
80 |
20 |
200 |
|
|
Days of growth |
157 |
150 |
90 |
90 |
247 |
240 |
|
|
N° of rotations |
4 |
4 |
2 |
2 |
6 |
6 |
|
|
Net pasture yield: |
|||||||
|
|
DM (t ha-1) |
9.68 |
9.85 |
2.90 |
3.42 |
12.6 |
13.3 |
|
|
Clover (t ha-1) |
4.33 |
3.05 |
1.50 |
1.28 |
5.8 |
4.3 |
|
|
(%) |
45 |
31 |
52 |
37 |
46 |
32 |
|
Grazing pressure: |
|||||||
|
|
(cows ha-1) |
4.00 |
4.53 |
2.20 |
2.26 |
3.34 |
3.68 |
|
Intake: |
|||||||
|
|
(t ha-1) |
8.37 |
888 |
2.54 |
3.13 |
10.9 |
12.0 |
|
|
(kg head-1 day-1) |
13.3 |
13.1 |
12.8 |
15.4 |
13.2 |
13.6 |
|
|
Net pasture utilization (%) |
86 |
90 |
87 |
91 |
86 |
90 |
Levels of DM yield from the mixed sward are good for the standards of the region. The response to N (N 200 minus N 20) was very low, 4 kg DM per kg N, and clover content was reduced from 46 to 32%. Treatments with N applied were grazed normally in shorter intervals than treatments without N, allowing more paddocks out from the grazing rotation and cut for silage in spring. Despite this low response from pasture, an important difference in grazing pressure was set in spring, 4.53 cows ha-1 in the pasture with N and 4.00 cows ha-1 in the mixed sward, due to the decisions made for grazing at a predetermined pasture height, at entrance and exit from the paddock, to obtain a similar level of pasture utilization in both treatments. This management was good to maintain a good clover content and a high quality leafly pasture.
The result was a similar intake (Table 1) and milk production per cow (Table 2) for the season. The differences in stocking rate lead to a higher milk yield per ha in spring when all cows were at the peak of production.
A total of 125 days of silage feeding was needed when cattle were indoors in late summer (September) and winter (December to February). It was obtained from 2.5 ha available in each treatment for silage cutting in spring. The annual stocking rate (Table 2) was used for calculating the milk yield per ha.
Table 2. Milk production from mixed sward
|
Treatments |
A |
B | |
|
N applied (kg ha-1) |
20 |
200 | |
|
Grazing pressure: |
|
| |
|
|
Annual Mean (cow ha-1) |
3.34 |
3.68 |
|
|
Stocking rate (cow ha-1) |
2.14 |
2.29 |
|
Milk yield: |
|
| |
|
|
l cow ha-1 |
4130 |
4060 |
|
|
l ha-1 |
8840 |
9300 |
The use of N (200 kg ha-1) gave an annual increase in milk yield per ha of 460 l due mainly to the different grazing pressure. Figure 1 shows the weekly milk production per cow per day in both treatments. Despite the similar management in both groups, a drop in milk yield was observed in the August rotation for treatment B, i.e. grazing the N paddocks. At that time differences in clover content in both treatments were not very high, 75% and 60% for A and B, respectively. Measured levels of intake were lower in group B than A, but theoretically sufficient for both.
Silage as the only feed in September was not good enough to maintain levels of milk yield. Milk production recovered when the cows returned to pasture in autumn.
Good milk yields can be obtained from grazing a grass/white clover sward with a high level of clover content and a low level use of concentrate feeding.
Management is a very important tool and grazing flexibility is required for clover maintenance and pasture quality.
The use of fertilizer N on a mixed sward gives a low DM yield response but allows the possibility of a small increase in the annual stocking rate, and as a consequence, a slightly higher milk yield per ha can be obtained.
Considering the low increment of milk production and the need to increase the stocking rate the economy of N application may not always be favourable.
Figure 1. Milk production per month on a grass/clover sward at two N rates
The work presented was done as part of the UE project AIR3-CT 92-0332
BAX, J.A. and SCHILS, R.L.M. (1993). Animal responses to white clover. In White Clover in Europe: State of the Art. FAO REUR Technical Series, 29, 7-16.
GONZALEZ-RODRIGUEZ, A. (1991). Animal production systems based on grass/clover swards. In White Clover Development in Europe. FAO REUR Technical Series, 19, 117-128
