Factors affecting pasture productivity in topographically variable landscapes: implications for pasture input management

Seventy-three sampling locations (38 on the north-aspect, 35 on the south-aspect) in a topographically variable landscape paddock on the Central Tablelands of NSW were monitored to determine the effect of soil chemical and physical parameters and botanical composition characteristics on pasture production. Stratification of sampling points into regions based on landscape features (aspect and position on slope) showed pasture production varied significantly between strata within the paddock. In some instances, the difference in production between strata was greater than between aspects and was attributable to a combination of soil physical (principally those associated with waterholding capacity) and botanical composition (legume content) factors. Exchangeable aluminium, while not identified as an indicator of pasture productivity in initial analysis, was the main determinant of production when only soil chemical parameters were considered. Exchangeable aluminium in association with ability of soil to hold moisture were found to strongly influence legume content. The results of this study indicate that greater consideration of a range of factors, other than soil available P, are required to determine pasture production potential in variable landscapes. Further, researchers and advisors need to be cognisant of such factors in determining optimum fertiliser application strategies in such landscapes to optimise pasture production, livestock production and economic return on investment. This is particularly important as concurrent studies at this site found that, despite deficiency of available phosphors at all sampling locations, only two regional strata were responsive to P-application. The study findings also highlight the insidious impact soil acidity and associated aluminium toxicity on pasture production in high rainfall regions of southern Australia.