On-farm assessment of environmental and management factors influencing wheat grain quality in the Mallee

Abstract

We used data from 63 grower-managed wheat crops during 3 growing seasons in the Mallee to explore grain protein responses to environmental and management factors. Allometric coefficients were calculated as the slope of the regression between the mass of log-transformed protein and non-protein grain components to account for the effect of ontogenetic drift on grain protein concentration. Test weight and screenings were also investigated.

Grain protein concentration ranged from 8.7 to 16.2%; 90% of crops had less than 5% screenings, and 95% had test weight above 74 kg/hL. Screenings increased and test weight declined with increasing concentration of protein, particularly for protein concentration above 13%. Fourteen cultivars were represented in the sampled crops. In comparison with crops of varieties eligible as Australian Premium White, crops of hard wheats had greater protein content, more screenings, lower test weight, and a greater protein : non-protein allometric coefficient, indicating differences in the pattern of protein allocation between these groups of cultivars.

Protein concentration declined with increasing yield at a rate ª1%/t.ha. It decreased with increasing seasonal rainfall at a rate of 0.014%/mm, and increased with the proportion of water stored below 0.5 m at a rate of 0.121%/%. Delayed sowing between mid April and mid July generated a size-dependent increase in grain protein concentration of 0.027%/day. Increasing protein content could attenuate the profit lost due to delayed sowing by up to AU$39/ha in hard wheats.

Wheat grown after legumes accumulated 64% more protein and 47% more non-protein material in the grain than their counterparts grown after cereal, and grain protein concentrations averaged 13.3 and 12.2% respectively. Protein concentration was unrelated to the amount of nitrogen in the whole soil profile (0-1 m), and weakly associated with the amount of initial nitrogen in the 0-0.1 m soil layer; it increased at a rate of 0.038%/kg N.ha. Chemical constraints in the subsoil probably affected the ability of the crop to use, and contributed to the accumulation of nitrogen in deep soil layers.