Wheat yields and indices of available soil nitrogen in Southern NSW – A preliminary evaluation

Linear regression analyses were used to evaluate the usefulness of a number of measures of the available soil nitrogen in accounting for the variability in wheat yields under field conditions in southern New South Wales. Single soil tests, such as total mineral nitrogen in the surface sample (0-10 cm depth), could account for only 38 and 18.5 per cent of the variation in yield at flowering and harvest respectively. However, the Use of bilinear regression involving boiling water soluble nitrogen in the surface horizon and nitrate-nitrogen in the sub-soil (10-30 cm depth) accounted for 64 and 36 per cent of the variation in yield at flowering and harvest respectively. The use of these tests to predict the nitrogen fertilizer requirement of wheat will necessitate the measure ment of climatic, cultural and edaphic factors as well as response to nitrogen fertilizer.