Recovery in the soil-plant system of nitrogen from green manure applied on cabbage crop

The objective of this work was to determine, in the soil-plant system, the recovery efficiency of N derived from green manure applied on cabbage (Brassica oleracea) crop. The experiment was divided into two stages: the first one consisted of the straw production of jack bean (Canavalia ensiformis), velvet bean (Mucuna cinereum), and sorghum (Sorghum bicolor), in substrate enriched with N-15. The second stage consisted of the application of N-15-labeled green manure on the cabbage beds. Treatments consisted of: fresh residues of jack bean; fresh residues of velvet bean; fresh residues of sorghum; mixture of residues of jack bean, velvet bean, and sorghum at 1:1:1; and control without green manure addition. The N recovery in the soil-plant system was influenced by the green manure species used, and the recovery efficiency of the N derived from the green manure legumes varied from 9 to 16%. The jack bean treatment shows a greater recovery efficiency of nitrogen and, therefore, the best synchrony of N supply, by straw decomposition, with the cabbage crop demand.