The relationship of grain yield to vegetative growth and post-flowering leaf area in the wheat crop under conditions of limited soil moisture

Trials were conducted in 1961 and 1962 at Wagga Wagga in southern New South Wales to investigate the yield physiology of the wheat crop. Various cultural treatments were applied to a single variety (Heron). This paper covers aspects directly related to grain yield. In the rate of sowing and fertilizer trials relative differences in grain yield were invariably less than relative differences in total dry weight at or before flowering. In some cases increased vegetative growth depressed grain yield. These results appear to be mainly the consequence of increased post-flowering competition for limited soil moisture in denser crops. High soil nitrogen had an additional detrimental effect. When as a result of later sowing flowering was delayed, both vegetative growth and post-flowering plant water status decreased; as a consequence grain yield decreased with successively later sowings. For the 1962 crops, grain yield was closely correlated (r = 0.969**) with leaf area duration after flowering, which in turn was related to leaf area index at flowering and to the rate of senescence of photosynthetic tissue. Increased rates of senescence were usually associated with reduced post-flowering plant water status, as indicated by the relative turgidity of the leaves. These results are discussed in relation to the importance of numerical components of grain yield and to improvement of grain yield in the wheat crop.