Recurrence of yield and protein variation in the northern grains region

Abstract

Grain yield and protein maps of sorghum and wheat were collected over consecutive seasons at Jimbour (southern QLD) and at Gurley (northern NSW) to identify spatial and temporal changes in nitrogen (N) removal and N supply. The Jimbour site was cropped with sorghum for 3 years (1999-2001), and the Gurley site with wheat (1999) then fallowed into sorghum (2001). Grain yield variation was moderate to
high; coefficients of variation (CV) ranged from 12 to 30%. Protein variation was low for each site and season with CVs below 10%. At Jimbour, high applications of N fertiliser minimised temporal variation in grain protein. At Gurley, matching of N fertiliser with yield potential (based on soil depth) also resulted in a low temporal variation in protein. The low protein variation, both within seasons and between seasons, then contributed little to the temporal variations in N removal. Both sites had areas of stable variation but
low supplies of N; these were related to areas where moisture had pooled or where soil depth, and hence available soil moisture, limited yields. Unstable variation was associated with isolated trees, contour, or edge effects. Under these conditions, protein data may need to only be collected every 2-3 years.