Recovery of nitrogen from different sources following applications to winter wheat at and after anthesis

The effects of applying nitrogen (30 or 40 kg N/ha) to wheat crops at and after anthesis, after 200 kg N/ha had already been applied to the soil during stem extension, were studied in field experiments comprising complete factorial combinations of different cultivars, fungicide applications and nitrogen treatments. Actual recoveries of late-season fertilizer nitrogen (LSFN), as indicated by ¹⁵N studies, interacted with cultivar and fungicide treatment, and depended on nitrogen source (urea applied as a solution to the foliage, or as ammonium nitrate applied to the soil) and year. These interactions, however, were not reflected in apparent fertilizer recoveries ((N in grain with LSFN − N in grain without LSFN)/N applied as LSFN), or in the crude protein concentration. Apparent fertilizer recovery was always lower than actual recoveries, and declined during grain filling. Fertilizer treatments with higher actual fertilizer recoveries were associated with lower net remobilisation of non-LSFN (net remobilised N = N in above ground crop at anthesis − N in non-grain, above ground crop at harvest). LSFN also increased mineral nitrogen in the soil at harvest even when applied as a solution to the foliage. These effects are discussed in relation to potential grain N demand.