THE EFFECT OF CUTTING HEIGHT AND MANAGEMENT SYSTEM ON THE PERFORMANCE OF A GRASS/CLOVER SWARD - R.L.M. Schils and K. Sikkem

Research Station for Cattle, Sheep and Horse Husbandry, Runderweg 6, 8219 PK Lelystad, The Netherlands

SUMMARY

The effect of cutting height on the dry matter (DM) yield of a perennial ryegrass/white clover sward was studied for three years in a cutting experiment on sandy soil. The treatments were all combinations of two rates of nitrogen (N) application in spring (0 or 100 kg ha^-1), two cutting heights (4-5 or 7-8 cm) and four management systems. The management systems consisted of four combinations of silage cuts (2 500-3 000 kg DM ha^-1) and simulated gratings (1 000-1 500 kg DM ha^-1) only silage cuts (SSSSS), only grazing (ggggggg) and two systems with successive silage cutting and grazing (SggSgg and gSggSg). In management systems SSSSS and ggggggg, the contrasting cutting heights were imposed on all cuts, but in management systems SggSgg and gSggSg, they were only imposed on the silage cut, while the simulated grazing cuts were always cut at a high cutting height.

In the management system with the contrasting cutting height imposed on all cuts (SSSSS and ggggggg), white clover DM yields were 2.2 t ha^-1 year^-1 higher with a low cutting height than with a high cutting height, but grass DM yields were hardly affected. In the three consecutive years, close cutting increased the average proportion of white clover in the herbage with 5, 3 and 20 percent, respectively compared to lax cutting. In the management systems in which the contrasting cutting height was only imposed on the two silage cuts (SggSgg and gSggSg), the average DM yield of white clover was 1.0 t ha^-1 higher with the low cutting height. The average proportion of white clover increased by 5 percent due to close cutting. It was concluded that there is some scope for farmers to use the cutting height to affect the white clover content in their swards.

Keywords: cutting frequency, cutting height, management system, perennial ryegrass, white clover.

INTRODUCTION

Recent developments in the Netherlands, like the introduction of milk quotas, growing interest in organic fanning and concern about nitrogen (N) losses are bringing about a gradual decrease in the use of fertilizer N. Although this encourages the use of mixed swards, many farmers are still reluctant to introduce white clover in their swards, partly because mixed swards are often associated with unpredictability and unreliability due to the large variation in their clover content. To attain some control over their swards, farmers need practical management tools that can affect the balance between grass and clover. Frame and Boyd (1937) and Acuna and Wilman (1993) have shown that cutting height affects the clover content in mixed swards. In these experiments, the different cutting heights were imposed on all cuts. However, in a typical Dutch grassland management system, paddocks are alternately cut for silage and grazed with dairy cows. Thus, there is only a limited number of opportunities in which the cutting height can be used to manipulate the clover content. The present experiment was conducted to determine the effect of cutting height on herbage yield and clover content, in a management system with alternative silage cutting and simulated grazing.

MATERIALS AND METHODS

In June 1994 a new sward was established on a sandy soil at the Aver Heino experimental station, using a seed mixture of 20 kg perennial ryegrass (Lolium perenne L. cvs, Herby and Exito) and 5 kg white clover (Trifolium repens L., cvs, Alice and Retor) per ha. During the establishment year three light silage cuts were made and in November the field was grazed by young stock. At the start of the experiment in March 1995, the top soil (0-5 cm) had a pH-KCl of 4.8 and an organic matter content of 6.1 percent.

The experiment, which ran from 1995 to 1997, consisted of all combinations of two rates of nitrogen (N) application in spring, four management systems and two cutting heights. The N applications were either 0 (N₀) or 100 (N₁₀₀) kg ha^-1, applied in March as calcium ammonium nitrate. The management systems consisted of four combinations of silage cuts (2 500-3 000 kg DM ha^-1) and simulated grazings (1 000-1 500 kg DM ha ^-1 i.e. only silage cuts (SSSSS), only grazing (ggggggg) and two systems with alternating silage cutting and grazing (SggSgg and gSggSg). The cutting heights were 4-5 cm (L) and 7-8 cm (H), measured with a falling plate meter. In management systems SSSSS and ggggggg, the low and high cutting height was imposed on all cuts. In order to obtain an improved simulation of farm practice in management systems SggSgg and gSggSg, the low and high cutting height were only imposed in the silage cuts, while the simulated grazing cut was always cut at a high cutting height.

The plats of 9 m² were harvested with a Haldrup harvester and herbage was weighed and sampled for determination of DM. An additional sample was taken for separation of grass and clover. A visual estimate of the ground cover of all plant species was performed every spring and in the autumn of the final year.

Weather data were collected on the experimental farm. The accumulated precipitation surpluses, from March to October, were -48, -72, and -55 mm in 1995, 1996 and 1997, respectively. Compared to the 30 year mean, the winter of 1994/1995 was wet and mild while the winters of 1995/1996 and 1996/1997 were both cold and dry.

RESULTS AND DISCUSSION

The productivity of the sward varied considerably between the three experimental years. In the first year the average annual DM yield was 13.73 t ha^-1 with 60 percent white clover. During the winter of 1995/1996, clover content decreased dramatically and the average annual DM yield was only 9.86 t ha ^-1 with 31 percent white clover. In the final year, white clover content remained at a similar level (33 percent), but the average annual DM yield increased to 12.19 ha^-1.

Application of N increased the annual DM yield by 93 kg per kg applied N, which was in line with earlier findings on the same site (Schils, 1997). As there were no noteworthy interactions between N application rate and the other treatments, it is not considered further in this paper.

Table 1. Annual total herbage DM yield, white clover DM yield and white clover content in DM, in relation to management system and cutting (L and H), averaged over N application rates.

a,b: different letters indicate significant differences (P<0.05) between cutting height within management system.

In the management systems with the contrasting cutting height imposed on all cuts (SSSSS an ggggggg), white clover DM yields and total herbage DM yields were consistently higher with the low than with the high cutting height (Table 1). In system SSSSS, the difference in clover DM yield was 2.5 t ha^-1 between the two cutting heights, and in system ggggggg the difference was 1.9 t ha^-1. As the grass DM yields were hardly affected by cutting height, approximately the same differences were found in total herbage DM yields. In the three consecutive years, close cutting increased the average proportion of white clover in the herbage by 5.8 and 20 percent, respectively, compared to lax cutting. These findings agree well with the earlier results of Frame and Boyd (1987) and Acuna and Wilman (1993).

Not surprisingly, the effect of cutting height was less pronounced and less consistent in the management systems in which the contrasting cutting height was only imposed on the two silage cuts (SggSgg and gSggSg).

The average DM yield of white clover was 1.0 t ha^-1 higher when the silage cuts were cut at low cutting height (Table 1). Again, the grass DM yields were hardly affected by cutting height. Within these management systems, close cutting of the silage cuts increased the proportion of white clover by 5 percent compared to lax cutting. There was no indication that the effect of cuffing height increased over the years, as observed in management systems SSSSS and ggggggg.

The seasonal white clover content in management systems SggSgg and gSggSg is presented in Figure 1. In most cases, close cutting favoured the white clover content in comparison to lax cutting. However, as the following cuts were simulated, grazings with a high cutting height, the positive effect on clover content was usually only temporary.

Figure 1. White clover content in management systems SggSgg (left) and gSggSg (right) with a low and high cutting height imposed on silage cuts only. Data are averaged over two N application rates.

Throughout the experiment, white clover and perennial regress were the dominating species, accounting for 90 percent of the species present. Cutting height had no effect on the presence of other species, the most important of which were annual meadow grass (Poa annua L.) and rough stalked meadow grass (Poa trivially L.).

The results of the present experiment show there is some scope for farmers to use the cutting height to manipulate the white clover content in their swards. At present, the recommended cutting height for grass is 5-6 cm, which is already quite favourable to white clover. If circumstances permit, i.e. an even surface and no expected drought, grass/clover swards can be cut at 4-5 cm to encourage clover growth. On the other hand, Iax cutting is a practical option where clover is becoming too dominant, although it will be at the cost of some DM yield. Under grazing, there is less control over the height of defoliation than there is with cutting. Farmers will be reluctant to use dairy cattle to achieve a stubble height of 4-5 cm, as that might negatively affect herbage intake. Unless sheep or young stock are available, silage cutting will be the most practical opportunity to affect the white clover content in a sward.

REFERENCES

Acuna, P., G.H. & Wilman, D. 1993. Effects of cutting height on the productivity and composition of perennial ryegrass-white clover swards. Journal of Agricultural Science, Cambridge 121, 29-37.

Frame, I. & Boyd, A.G. 1987. The effect of fertilizer nitrogen rate, white clover variety and closeness of cutting on herbage productivity from perennial ryegrass/white clover swards. Grass and Forage Science 42, 35-96.

Schils, R.L.M. 1997. Effect of a spring application of nitrogen on the performance of perennial ryegrass-white clover swards at two sites in the Netherlands. Netherlands Journal of Agricultural Science, 45, 263-275.