EFFECT OF SEMI-EXTENSIVE PASTURE MANAGEMENT ON ITS BOTANICAL COMPOSITION AND ANIMAL PRODUCTION - M. Michalec, M. Zimková and O. Jezíková

Grassland and Mountain Agriculture Research Institute, Mládeznícka 36, 974 21 Banská Bystrica, Slovakia

SUMMARY

A grazing trial with heifers was conducted at Nemecká, Central Slovakia in 1986-89 (520 m; average annual rainfall 727 mm, during the growing season 424 mm; average annual temperature 6.3°C, during the growing season 13°C). The sward was semi-natural grassland, Poo-Trisetetum; fertilization: 120 kg N ha^-1 + 35 kg P ha^-1 annually.

Two systems of grazing were compared:

A. Heifers grazing on a young sward - the main grass species Poa pratensis, Lolium perenne, Festuca pratensis at the stage of tillering - in six paddocks with N-fertilization of 3 x 40 kg N ha^-1.

B. Heifers grazing on an older sward - the dominant grass species (Poa pratensis) at flowering - in three paddocks with fertilization 2 x 60 kg N ha^-1.

The different management and sward utilization (three or six paddocks) and the differently applied N-fertilization influenced the botanical composition and yield of the sward, liveweight gains (LWG) and meat production per ha. The main tendency in botanical composition of system A was: decrease of grass and herb species and increase of legumes; and of system B: amount of grass species stable, slow increase of legumes and decrease of herbs. The percentage of Trifolium repens reached a maximum of 24 percent (system A, 3rd grazing cycle in 1989).

Liveweight gains were 605 and 580 g head^-1 day^-1 for systems A and B, respectively. Corresponding stocking rates were 3.11 and 3.23 head ha^-1 and average meat production, 448 and 433 kg ha^-1.

Keywords: semi-extensive pasture management, botanical composition, grazing, liveweight gain, meat production

INTRODUCTION

Extensification is being called for in many European countries. This implies low inputs of fertilizers and semi-extensive systems of grazing. Within this scenario biodiversity in sward composition is likely and white clover has an important role to play in both its N-fixing and high nutritive value characteristics. This study aimed to quantify the botanical composition and meat production of semi-natural pasture under semi-extensive management.

MATERIALS AND METHODS

The grazing trial with heifers was conducted at Nemecká (Central Slovakia): 520 m; average annual rainfall 727 mm, during the growing season 424 mm; average annual temperature 6.3°C, during the growing season 13°C, in 1986-89. The sward was semi-natural grassland, Poo-Trisetum. The terrain was of northern exposure with 5-7°C declination.

Two systems of grazing were compared:

A. Grazing of heifers (Slovak Spot Breed) on a young sward - the main grass species (Poa pratensis, Lolium perenne, Festuca pratensis) at the stage of tillering - in six paddocks (å 1.58 ha) with 3 x 40 kg N ha^-1 + 35 kg P ha^-1 applied.

B. Grazing of heifers on the older sward - the dominant grass species at flowering stage - in three paddocks with 2 x 60 kg N + 35 kg P ha^-1 applied.

Phosphorus fertilizer was applied each autumn and nitrogen after grazing the cycles (in system A after 1^st, 2^nd and 3^rd cycles and in system B after 1^st and 2^nd cycles). For the A and B systems the grazed area was 1.58 and 1.72 ha, respectively; animals being in one paddock 3-7 and 6-15 days, respectively.

Botanical composition was evaluated by projective dominance (subjective method of species assessment in percentage).

RESULTS AND DISCUSSION

The botanical composition of the swards is shown in Tables 1 and 2.

The dominant grass species was Poa pratensis, its percentage in the 1st grazing cycle being 32-40 and 31-37 for A and B grazing systems, respectively. In the 3rd grazing cycle the percentage of Poa pratensis decreased from 1986 to 1989 by 8 and 17 in the A and B management systems, respectively.

Table 1. Botanical composition of swards in the 1st grazing cycle (%).

Table 2. The botanical composition of swards in the 3rd grazing cycle (%).

Both management systems maintained the development of white clover in the sward; maximum percentage was assessed in the 3rd grazing cycle: 13-24 and 7-18 in A and B systems, respectively. An increasing percentage of white clover in the sward was found from 1986 to 1989: maximum 24 percent in A system in 1989. The dominant herb species was Taraxacum officinale whose highest percentage was in the 1st grazing cycle: 9-12 and 10-14 in A and B management systems, respectively.

Nösberger (1994) and Bakker (1994) have described the benefits of biodiversity potential from extensification methods, though extreme extensification is not the aim of production systems. Periodic oscillations in white clover content have been suggested as an indication that the sward-management-grazing animal complex is working well (Schwinning and Parsons, 1996).

The potential of semi-extensive pasture management depends also on stocking rate (Table 3). The higher stocking rate was in system B though there were differences between years; the lowest stocking rate was assessed in 1988 which was caused by lower forage production due to dry weather. The effect of semi-extensive pasture management on LWG was not as significant as expected (Table 4) but significant differences were found between years. The lowest daily LWG was in 1988: 520 and 490 g head^-1 day^-1 for systems A and B, respectively.

Table 3. Average stocking rate (heifers ha^-1) in 1986-89.

Table 4. Average daily LWG of heifers (g head^-1 d^-1).

Table 5. Meat production (kg ha^-1)

There were differences in beef production between the years, the lowest meat production being in 1988 and averages were 448 and 433 kg ha^-1 for systems A and B, respectively (Table 5). Good results of daily liveweight gains and beef production from grass/clover swards have also been demonstrated by Davies and Hopkins (1996).

REFERENCES

Bakker, J.P. 1994. Nature management in Dutch grasslands. Grassland Management and Nature Conservation. Occasional Symposium No 28. British Grassland Society, 115-124.

Davies, D.A. & Hopkins, A. 1996. Production benefits of legumes in grassland. In: Younie, D. (Ed.). Legumes in Sustainable Farming Systems. Occasional Symposium No 30. British Grassland Society, 234-246.

Nösberg et al. 1994. Grassland production system and nature conservation. Grassland and Society. Proceedings of the 15th General Meeting of the European Grassland Federation, 255-265.

Schwinning, S. & Parsons, A.J. 1996. Interaction between grasses and legumes: understanding variability in species composition. In: Younie, D. (Ed). Legumes in Sustainable Farming Systems. Occasional Symposium No 30. British Grassland Society, 153-163.