Managing rhodes grass (Chloris gayana) cv. Callide to improve diet quality. 2. Effects of stocking rate and irrigation frequency

Abstract

The effects of stocking rate and irrigation frequency on the milk production of cows grazing nitrogen-fertilised Callide rhodes grass pastures was studied in south-east Queensland. Pastures were stocked at 3.5, 5.25 and 6.1 cows/ha from January-May inclusive, and irrigated at fortnightly or monthly intervals.

Yields on offer pregrazing and pasture, leaf and stem residues after grazing decreased at the higher stocking rates. Consumption of grass leaf averaged 10.6, 7.7 and 6.5 kg DM/cow/d for cows grazed at 3.5, 5.25 and 6.1 cows/ha, respectively (P<0.05). Intake of stem averaged 1.3 kg DM/cow/d, with no difference between treatments (P>0.05). Milk yields averaged 16.6 kg/cow/d for Weeks 7-18 and were unaffected by treatment. Liveweight loss in the first 15 weeks of the experiment averaged 15, 28 and 43 kg at 3.5, 5.25 and 6.1 cows/ha, respectively (P<0.05). Cows stocked at 3.5/ha recovered liveweight during the experiment, but liveweight losses continued for cows at 5.25 and 6.1 cows/ha.

Rhodes grass management should aim to harvest a high proportion of leaf, a result which was achieved under a wide range of stocking rates in this experiment. Reducing the frequency and total volume of irrigation resulted in reduced levels of soil water and pasture yield, but did not affect milk production until the final 3 weeks of the experiment (May). The stocking rate of 3.5 cows/ha allowed cows to maintain body weight and appears optimal for these pastures. The ability of the pastures to maintain DM yield with half the applied water input demonstrates that efficiencies may be gained by closer monitoring of soil and pasture production in autumn rather than the normal practice of fortnightly watering. This, combined with the longer grazing interval of 6 weeks and a stocking rate of 3.5 cows/ha, provided the most efficient use of the tropical grass pasture resource in late summer and autumn.