Managing roots, nitrogen and fungicides to improve yield and quality of wheat

Abstract

The major aim of this project was to determine whether root growth, distribution and activity late in the growing season (particularly after flowering) influence grain yield and quality of cultivars in response to fungicide and late-season nitrogen applications.  Four experiments were carried out over three seasons on a free-draining sandy loam overlying sand at the Crops Research Unit of the University of Reading. These investigated the effects of cultivar, irrigation/drought, fungicide applications, and late-season nitrogen applications to soil or foliage on root growth and distribution, canopy green area duration, grain yield, grain quality, and root activity in nitrogen uptake from the soil.

When fungicides were applied, the size of root system was maintained during early grain-filling, and root length typically increased. There were significant differences between cultivars in the quantity of roots below 30 cm depth. Shamrock had the longest root system. Fungicide applications had small, but seasonally variable, effects on root growth but consistently increased green leaf area duration. Application at flag leaf emergence generally gave good control of all diseases with little benefit from a further application at ear emergence. There were significant differences between cultivars with Consort being most responsive. Fungicide applications significantly increased grain yields (through increased thousand grain weight and specific weight) and grain N content by delaying leaf senescence via disease control.

There was no relation between grain yield and post-anthesis rooting extent or distribution, but the size of the root system during the post-anthesis period was related to late season N uptake and hence to grain quality. Grain yield and N content were related to green leaf area duration after anthesis (0.17 t grain ha-1 and 2.67 kg N ha-1for each day that the flag leaf remained green), although these benefits do not accrue indefinitely and were limited to a thermal time period less than 700 oCd after anthesis.

It is suggested that fungicide application may delay both senescence of leaves and of the root system, leading to increased N in the grain, either through continued uptake of N into the crop, or through retention of N in the plant that would otherwise leak from the plant. Overall, the results suggest that breeding/variety selection and agronomy could be exploited to optimise late-season rooting to use N more efficiently and to improve grain N content.