Fertilizer nitrogen budgets of 15N-labelled sugarbeet (Beta vulgaris) tops and Na 15NO3 dressings split-applied to winter wheat (Triticum aestivum) in microplots on a loam soil

The fate of N from sugarbeet (Beta vulgaris L.) tops returned to the soil (50 T ha^-1) in autumn 1986 before sowing winter wheat (Triticum aestivum L.), and from NaNO₃ split-applied in 3 equal dressings (at tillering, stem elongation and flag leaf stages) was studied using isotopically labelled ¹⁵N in open stainless-steel cylinders pressed into the soil.At harvest, the percentage utilization (PU) of N from sugarbeet was very low (6.66%) and negatively influenced by fertilizer N (5.59%), while that of fertilizer N was rather high (69.64%) and unchanged by addition of tops. Residual N in soil represented 25.9% of the amount applied in tops and ranged from 33% for the tillering application to 21% for the flag leaf application. N losses (mainly denitrification) from sugar beet tops amounted to 67% and were very low for mineral fertilizer (less than 5%).