This study was carried out under laboratory conditions from September to December, 1992. The objective was to evaluate the mineralization of nitrogen in cowpea (Vigna unguiculata L.) green manure, using 15N as tracer, in three major soils of Central Amazon: an Oxisol, an Ultisol and a Low-Humic Gley. The variation in amount and form of the mineral N from cowpea residues was related to the chemical characteristics of each soil. In the Oxisol and Ultisol the incorporation of green manure increased N mineralization significantly, and the ammonium form was predominant in both soils, while in the Humic Gley it was the nitrate form. Cowpea incorporation increased the rate of organic nitrogen mineralization, suggesting the occurrence of priming effects. After 60 days of incubation, approximately 30% (Utisol) to 40% (Oxisol) of the N from green manure was mineralized, and in the Humic Gley 18%. The results demonstrated the good potential of cowpea as green manure for the Oxisol and Ultisol of Central Amazon.
15N-labelled; cowpea (Vigna unguiculata L.); mineralization; priming effect; Oxisol; Ultisol; Low-Humic Gley (Inceptisol); Central Amazon