The ecology and utilization of dryland lucerne pastures on deep sands in the Upper South East of South Australia

A grazing experiment involving Merino wethers in several stocking rate (SR) and grazing method (GM) treatment combinations was undertaken on pastures based on dryland lucerne (cv. Hunter River) at Kynoch Station on deep sandy soils in the Upper South East of South Australia (Mediterranean climate with 420-450 mm average annual rainfall). Merino wethers were grazed for four years (1967-70) to assess treatment effects on lucerne production and persistence, animal performance and potential soil erosion. There were twelve main treatments. Stocking rates of 2 (low), 3 (medium-low), 4 (medium-high) and 5 (high) wethers/ha were used. Grazing method included four t reatments , the extremes being a 6-paddock rotational treatment and a continuous grazing treatment (compared at a11 stocking rates). Intermediate grazing method treatments were a 3-paddock rotational system and a set-stocked winter-6-paddock summer treatment (these treatments were only at the two intermediate stocking rates). Lucerne was t he key to productivity and thus the focus of the interrelationships between stocking rate and grazing method in the ecosystan. Animal performance in the longer term was directly related to lucerne performance. Stocking rate and grazing method both affected lucerne production and persistence. Furthermore, significant SR x GM interactions occurred. Thus at the medium-low stocking rate, only the continuous grazing method significantly depressed lucerne production and density during the experiment. However, at the medium-high stocking rate only the 6-paddock grazing method maintained adequate lucerne production and density. The SR x GM interaction .was also reflected in body weight and wool production of the wethers i.e. the higher the stocking·xate, the more important was a rotational grazing method to maintain long term animal production. Lucerne affected animal production by minimizing both body weight loss and t he reduction of wool growth rates during the summerautumn period. The degree of maintenance of such animal performance depended on amount of lucerne growth, which was largely affected by the amount of out-of-season rainfall. The period of the experiment: included the 1967 drought (lowest rainfall in 64 years of recording in surrounding areas) . That lucerne was able to survive and recover from the effects of this drought indicates the long term viability of lucerne in these deep sand regions provided attention is paid to grazing management. Subsidiary treatments started in December 1968 (following the drought) with stocking rates up to 7.5 wethers/ha indicated that in an average period of years, the effects shown by the treatments in the main experiment could be expected to have occurred at 50-100% higher stocking rates. The Kynoch experiment showed clearly the dangers of set stocking during winter-early spring, especially at higher stocking rates and in poorer years. Although short term advantages in animal production may be obtained these are counteracted by the longer-term costs of reduced production from the lucerne stand and/or the need for re-establishment of the lucerne (with inherent risks of soil erosion). At the highest stocking rate even the 6-paddock rotation was inadequate during severe s tress periods to protect the lucerne from irreparable damage from the grazing animal. Methods of overcoming this problem and thus minimizing soil erosion hazards are suggested. Grazing method and stocking rate, through their effects on lucerne production and persistence, also greatly affected the yield and ground cover of other species in the pasture. The rate of soil water usage, the degree of soil water storage and the amount of soil water drainage in the deep sand profile were also affected by grazing treatments. Lucerne is particularly suited to the deep sand environment largely because of its ability to utilize soil water at depthy and to respond to out-of-season rainfall. The soil water characteristics of the deep sands are such as to allow growth response by lucerne to very l ittle (c. 5 mm) rainfall. Despite initial correction of phosphorus, copper, zinc, cobalt and molybdenum deficiencies on the deep sands, major deficiencies of nitrogen (largely affecting grass production) and potassium (largely affecting subterranean clover production) still occur. However, lucerne overcomes these deficiencies and hence it has a competitive advantage over other species. The wide economic implications from the Kynoch experiment on t he utilization by grazing animals of dryland lucerne pasture on deep sands are discussed in terms of various enterprises. Although the experiment involved only wool-producing wethers, it is considered that the pastures would allow highly successful alternative production of young animals, whether t hese be replacement wool-producing sheep, prime lambs or yearling beef cattle.Thesis (M.Agric.Sc) -- University of Adelaide, Faculty of Agricultural Science, 197