Genotype, sowing date and plant spacing influence on high-yielding irrigated wheat in southern New South Wales. II. Growth, yield and nitrogen use

Sowing date, sowing rate and row spacing effects were studied on irrigated wheat crops at Griffith, N.S.W. during 1983-85 using genotypes differing in maturity, stature and genetic background. The aim was to identify better management practices and genotypes through a better understanding of development and growth of wheat grown under high-yielding conditions. Maximum yield was up to 891 g/m2. The average yield reduction was 50 g/m2 or 6% per 1-week delay in anthesis after 1 October, but varied between 2 and 23%, depending on the season. Lodging was a significant problem in all three years, with less lodging for later sowing dates, earlier maturity types or shorter stature. Plant spacing, through variations in row spacing (17-45 cm) or sowing rate (50-200 kg/ha) did not significantly affect grain yields, but lodging was reduced by increased row spacing and reduced sowing rate. Dry weight at anthesis (600-1 500 g/m2) explained 65% of the variation in lodging, with severe lodging risks for weights over 900 g/m2. Harvest index improved with later sowing or earlier maturity and was, among genotypes within a sowing, negatively correlated with anthesis date, height, lodging score and final leaf number on the main stem. Nitrogen uptake usually ceased before anthesis. Genotypic differences in grain protein concentrations of more than 2% were found. Some genotypes combined high yield with high grain protein concentration (e.g. 717 g/m2, 14.1% protein). Significant genotype effects on spike density, kernel weight, kernel growth rate, and number of kernels per m2, per spike and per g chaff weight were identified, but none seemed to restrict yield. There was much compensation between traits. For example, high kernel numbers (per g chaff, spike or m2) were associated with low kernel weights and vice versa, both within and between genotypes. It was concluded that short-stature, early-maturing, low spike-bearing cultivars are most suited to high-yielding conditions from any sowing date, provided flowering occurs after late September, as such crops have a reduced lodging risk and use assimilates and N most efficiently. Genotypes were highly adaptable and many morphogenetic traits differed widely between genotypes, but were usually similar among dwarf or semidwarf, and among early or late maturing genotypes.