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GrainGenes Reference Report: AAR-55-645

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Reference	AAR-55-645
Title	The impact of agronomic manipulation of early vigour in wheat on growth and yield in South Australia
Journal	Australian Journal of Agricultural Research
Year	2004
Volume	55
Pages	645-654
Author	Sloane DHG Gill GS McDonald GK
Abstract	The initial growth of wheat crops can be manipulated either by agronomic means, such as by increasing inputs of seed and fertiliser, or by genetic improvement in early vigour. Cultivars of wheat with enhanced early vigour are still not commercially available and so a series of experiments was conducted to examine the impact of increasing initial dry matter production and leaf area index by increasing sowing and nitrogen (N) rates on grain yield. Increasing the sowing rate and amount of N fertiliser applied significantly increased early dry matter production and leaf area, with the largest responses occurring when sowing rate was increased. However, there was little effect on yield. The increases in dry matter production that occurred early in the season as a result of the additional inputs diminished as the season progressed. Yield responses to the additional inputs depended on the seasonal distribution of rainfall and in particular the rainfall received in August and September when grains per m2 were being determined. Consequently, yield responses were affected more by changes in grain per m2 than by changes in grain weight, and the benefits of the improvements in early vigour were only realised when moisture availability was high during the immediate pre-anthesis and early grain filling period of growth. High rainfall in August and September increased the responses in grains per m2 from increased sowing rate and N. When N was used to increase early growth, the response in grain weight was negatively correlated with increasing pre-anthesis rainfall, but there was no relationship with rainfall when sowing rate was used to increase early growth. This effect of N, in which responses in pre-anthesis growth were offset by reductions in grain weight, is consistent with the 'haying-off' effect that can occur with applications of N. The results showed that increasing early vigour by increased inputs of seed and N fertiliser produce variable responses in grain yield. While improvements in vegetative growth occurred, the realisation of these gains only happened when rainfall in August and September was adequate. Basing improvements in early vigour only on agronomic manipulation appears to be associated with a relatively high level of risk, as it is difficult to control the balance between vegetative growth and the availability of soil moisture. Alternatively, the data suggest that the levels of early vigour under current agronomic practices may be adequate (>50 g/m2 shoot DM at late tillering stage), and only marginal gains may be achieved by promoting early growth by additional inputs
Keyword	[ Hide all but 1 of 54 ] area australia availability barley production control dry matter dry matter production dryland wheat early vigour fertiliser fertilizer filling period gain grain filling grain weight grain yield grains growth impact improvement improvements index inputs leaf area leaf area index leaf-area manipulation matter moisture nitrogen northern syria period production rain-fed conditions rainfall rate reduction responses risk seed so soil soil moisture soil-moisture sowing sowing rate tillering triticum aestivum vegetative growth water-use efficiency winter wheat yield yield response yield responses

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