Theme 22: Grazing Management
Description
The aim of this study was to search the effects of grazing intensity and nitrogen fertilization on the structural stability of a mixed pasture composed by alfalfa (latency group 9), brome grass, tall fescue and white clover, sown in April 1997. Rotational grazing was carried out with dairy cattle with high intensity (HI: up to 3-4 cm) or moderate intensity (LI: up to 8-10 cm), whenever the alfalfa showed basal regrowth. According to a split-plot design, grazing intensities were subdivided to assign three levels of nitrogen fertilization: N0, without fertilization; N1 with 50 kg N/ha per year; and N2 with 100 kg N/ha per year, its supplied at the beginning of autumn and at the end of winter. The botanical composition (%), module density (number per m2) and basal cover (%) before grazing were measured from September 1997 through December 1999. After 20 grazing periods the use intensity affected significantly (p< 0.05) all the variables, while N had minor effect. The average alfalfa content changed from 46.8% to 11.0% in HI, and 25.0% in LI in November 1999; fescue from 15.3% to 5.3% and 36% respectively; brome grass from 28.1% to 65% and 21.7% respectively; and perennial weeds from 4.3% to 8.3% and 6.3% respectively; the rest being dead material. The white clover practically disappeared during the drought of the second summer. The pasture basal cover showed an evolution from 21% to 20.7% in HI and 95% in LI in December 1999; the weed Bermuda grass from 15% to 68.8% and 3.3%, respectively, and the bare soil from 63.9% to 8.2% and 0.5%, respectively. The total module density of alfalfa, tall fescue and brome grass was dramatically reduced from a global mean of 577 mod per m2 to 79 in HI and 152 in LI.
Included in
Structural Stability of Short Latency Alfalfa-Based Pastures in the Humid Pampa, Argentina
The aim of this study was to search the effects of grazing intensity and nitrogen fertilization on the structural stability of a mixed pasture composed by alfalfa (latency group 9), brome grass, tall fescue and white clover, sown in April 1997. Rotational grazing was carried out with dairy cattle with high intensity (HI: up to 3-4 cm) or moderate intensity (LI: up to 8-10 cm), whenever the alfalfa showed basal regrowth. According to a split-plot design, grazing intensities were subdivided to assign three levels of nitrogen fertilization: N0, without fertilization; N1 with 50 kg N/ha per year; and N2 with 100 kg N/ha per year, its supplied at the beginning of autumn and at the end of winter. The botanical composition (%), module density (number per m2) and basal cover (%) before grazing were measured from September 1997 through December 1999. After 20 grazing periods the use intensity affected significantly (p< 0.05) all the variables, while N had minor effect. The average alfalfa content changed from 46.8% to 11.0% in HI, and 25.0% in LI in November 1999; fescue from 15.3% to 5.3% and 36% respectively; brome grass from 28.1% to 65% and 21.7% respectively; and perennial weeds from 4.3% to 8.3% and 6.3% respectively; the rest being dead material. The white clover practically disappeared during the drought of the second summer. The pasture basal cover showed an evolution from 21% to 20.7% in HI and 95% in LI in December 1999; the weed Bermuda grass from 15% to 68.8% and 3.3%, respectively, and the bare soil from 63.9% to 8.2% and 0.5%, respectively. The total module density of alfalfa, tall fescue and brome grass was dramatically reduced from a global mean of 577 mod per m2 to 79 in HI and 152 in LI.
