Recovery of 15N‐labelled urea applied to the foliage of winter wheat

Abstract

¹⁵N‐labelled urea (30 kg N ha⁻¹) was sprayed on to the foliage of winter wheat at four sites where sufficient fertiliser N had previously been applied to the soil to achieve approximately maximum yield. Half of the urea was applied shortly before anthesis (growth stage, GS, 37‐39) and half after anthesis (GS 69–73), both portions being labelled. Averaged over all sites, 62% of the urea N was recovered in the crop (range: 45–77%). On average, 89% of the urea N recovered in the crop was in grain, a rather greater proportion than from applications of N to soil in spring. Foliar‐applied N (30 kg ha⁻¹) increased %N in grain as much as an additional 60 kg N ha⁻¹ applied to soil in February but slightly less than an extra 60 kg ha⁻¹ applied to soil in April. Foliar N did not alter yield or 1000 grain weight at any site, and where a breadmaking wheat (cv. Avalon) was grown had no adverse effect on Hagberg Falling Number or grain nitrogen/sulphur ratio.