The effects of rates of stocking with rotational grazing on the productivity of dryland lucerne at Tamworth, New South Wales

Abstract

A two-year-old stand of Hunter River lucerne (Medicago sativa) at Tamworth Agricultura Research Centre was grazed for three years with dry ewes at five stocking rates (8-21 sheep ha-1) in a flexible rotational system with six paddocks. At each stocking rate, sheep were moved between paddocks on the basis of feed availability, and excess forage was harvested as hay. At the lowest stocking rate a fixed rotation with weekly moves and no harvesting of hay was also examined. Sheep were fed with hay when necessary to maintain mean body weight above 38.5 kg. Lucerne production under grazing was measured from temporarily exclosed areas under grazing and compared with the production from permanently exclosed areas. Up to the median stocking rate of 15 sheep ha-1 a surplus of hay remained at the end of the experiment. At higher stocking rates a deficit resulted and sheep body weights declined severely in autumn and winter in all treatments. The highest stocking rate of 21 sheep ha-1 was terminated after 18 months. Mean annual yield of clean wool increased linearly (P < 0.01) from 32 kg ha-1 at the lowest stocking rate to 45 kg ha-1 with 18 sheep ha-1. The decline of lucerne density was related to stocking rate but significant differences in density were not reflected in lucerne production. Lucerne production under grazing was strongly seasonal with the highest yields measured in spring and summer when hay was harvested. Although production in ungrazed exclosures was comparable with that of grazed areas in autumn and winter it was much greater during spring. It would appear that a more lenient system of grazing management is necessary during the cool months in this environment to maximize lucerne production during the spring and summer. This is feasible in the whole farm situation where alternate crops are available.