Abstract
Reduction of the amount of nitrogen (N) remaining in mature wheat straw is an essential challenge in order to boost grain protein and N use efficiency. However, very limited information is available on the composition of the residual N pools and how they are affected by N fertilization. Winter wheat was grown under field conditions at five different N levels ranging from 60 to 280 kg N ha−1. The fraction of straw N present in amino acids, chlorophyll, DNA, nitrate and lignin-associated compounds were analyzed separately in leaf blades, sheaths and stems. Total straw N concentration increased from 0.29 to 0.69% with increasing level of N application. The largest N pool consisted of amino acids in hydrolysable proteins, which comprised 50 to 70% of the residual N. Lignin-associated, non-hydrolysable N compounds constituted 13 to 16% of the total N, while non-protein N pools (mainly chlorophyll breakdown products and DNA) amounted to 5–14%. Protein-derived amino acids constituted the most abundant N pool in mature wheat straw. Despite a 2.5-fold increase in total straw N content, the relative proportion of the different residual N pools to the total N content in the straw did not change with N fertilization.
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