A study of the relationships between the yield of irrigated lucerne and the properties of some grey and brown soils of heavy texture in south-west New South Wales

Abstract

Correlations between the yield of irrigated lucerne and specific properties of a sequence of grey and brown soils of heavy texture have been investigated under conditions of high superphosphate application and the normal watering regime of the district. Yield is strongly correlated with increment in available water per irrigation, which appears to be largely dependent on degree of cracking as controlled by clay content. A significant evaluation of differences in the chosen range of soils, therefore, would seem to be the status of accession of available water, but its measurement is long and tedious. Significant correlations between yield and more easily measured properties have been sought and found. The properties correlating with yield are clay, fine sand, apparent density, total exchangeable metal cations, exchangeable calcium, exchangeable potassium, and exchangeable sodium of the 1-4 in, layer and chloride and exchangeable potassium of the 8-12 in. layer. Because of a high degree of association between a number of these, the best yield prediction equation involves two only, viz. exchangeable calcium at 1-4 in. (XI as m-equiv./100 g) and chloride at 8-12 in. (X2 as %). The regression equation is Y = 85.1 + 28.3 X1 - 330.6 X2, accounting for 66% of the variability in yield. In the absence of data on exchangeable calcium, other properties closely correlated with it would have predictive value, e.g. clay content at 1-4 in. (X3 as %), the regression becoming Y = 98.5 - 266.1 X2 - 3.6 X3. The technique of seeking soil-plant relationships by direct experimentation is discussed briefly.