An evaluation of kikuyu-clover pastures as a dairy production system. 3. Dynamics of pasture composition and diet selection

Abstract

A dairy system based on irrigated, perennial kikuyu (Pennisetum clandestinum) cv. Whittet - white clover (Trifolium repens) cv. Haifa pasture was compared at various stocking rates and nitrogen (N) fertiliser rates in a 3-year experiment. In the final year, observations were taken on 4 treatments comprising: 2.5 cows/ha, 0 kg/ha N; 3.75 cows/ha, 150 kg/ha N; 5 cows/ha, 150 kg/ha N; and 5 cows/ha, 600 kg/ha N. Daily milk yield, and pasture on offer, pasture composition and diet selection on Days 0, 2, 5 and 7 of a 7 day grazing, 21 day spelling rotation were measured. Milk yields ranged from 10.6-15.5 kg/d in May (P<0.01) and from 16.9-21.7 kg/d in October (P<0.05). Peak milk yield occurred on Day 3 of the grazing cycle in May and Day 4 in October, with increases of 1.85 and 0.75 kg/d, respectively, relative to milk yield at the start of the cycle. Clover % in the diet (DCLOV%) on the first day of the grazing cycle was the factor most closely related to milk yield (MY; kg/d). The across-seasons equation, where MONTH - 0 for May and 1 for October, was: MY (kg/d) = 11.77 + 3.94 MONTH + 0.069 DCLOV % (R2 = 0.84; P<0.001).Clover % in the diet (DCLOV%) was most related to pasture clover yield on offer (PCLOVY) with declining coefficients of selection for each day of the rotation. Dietary crude protein % declined linearly with day of the rotation at approximately 1.4% per day, and calcium and magnesium selected from pasture were also observed to decrease with day of the grazing cycle.