POSTANTHESIS REMOBILIZATION AND LOSSES OF NITROGEN IN WHEAT IN RELATION TO APPLIED NITROGEN

A N-15 leaf feeding technique was used to measure the extent of remobilisation and loss of nitrogen (N) that had been accumulated prior to anthesis in wheat plants that received three rates of N fertilizer. Uptake of postanthesis N to the heads was reduced as the quantity of applied N was increased. This reduction of postanthesis N uptake did not affect the quantity of N in the heads because the loss of preanthesis accumulated N was reduced and the extent of remobilised preanthesis N increased at higher rates of N application. At the lowest rate of N application the increase in N-15 in the heads of fertile shoots arose chiefly from the remobilisation of N in the stem supporting the head. At higher rates of N application this source of N was increasingly supplemented by N remobilised from infertile tillers and roots.