Plant‐Available Nitrogen from Lentil and Wheat Residues during a Subsequent Growing Season

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Abstract
Lentil (Lens culinaris Medikus) is being grown increasingly on the Canadian prairies as a pulse or green manure crop, and may increase N availability to a succeeding crop. This study was designed to compare the effects of lentil green manure, lentil straw, and wheat (Triticum aestivum L.) straw on plant‐available N during the growing season after application. The fate of 15N from fall‐applied (1988) lentil green manure, lentil straw, and wheat straw and spring‐applied (1989) fertilizer (NH4)2 SO4 was determined four times during the 1989 growing season at a field site located at Outlook, Saskatchewan, Canada, on a Bradwell sandy loam (Typic Boroll). Denitrification and leaching losses of 15N from added lentil and wheat straw were negligible, but 24 and 30% of the 15N in lentil green manure and fertilizer, respectively, were lost in the 6‐wk period after planting (8 May 1989). By wheat harvest (8 Aug. 1989), 7% of the 15N in lentil and wheat straw and 37% of the 15N in lentil green manure were mineralized. Addition of green manure increased net mineralization of indigenous soil N at the time of planting by 0.4 g m−2, equivalent to 10% of added green manure N. Immobilization of soil and fertilizer N was similar for lentil and wheat straw. The smaller fraction of 15N assimilated from green manure (19%) than from fertilizer (34%) by wheat was due solely to less net mineralization of green‐manure N rather than net immobilization of fertilizer N. Of the 15N added in lentil and wheat straw, 5.5% was assimilated by wheat. Thus, lentil straw was not a significant source of N in this study, while ≈40% of the N in lentil green manure was potentially available for plant uptake.

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