RECOVERY OF LEUCAENA AND DACTYLADENIA RESIDUE N-15 IN ALLEY CROPPING SYSTEMS

Quantification of the fate of residue N is essential in low-input trop ical cropping systems for the development of management practices that optimize N-use efficiency. The recovery of N from N-15-labeled leucae na [Leucaena leucocephala (Lam.) de Wit] and dactyladenia [Dactyladeni a barteri (Hook f ex Oliv.) Engl.] leaf residues was followed in the s oil, crop, and hedgerow of the respective alley cropping systems durin g three maize (Zea mays L.) and two cowpea (Vigna unguiculata L. Walp. subsp. unguiculata) seasons. More residue N was recovered in the top 5 cm of soil in the leucaena than in the dactyladenia microplot during the first 471 d after residue application (DAA). The first maize crop recovered 8.6 and 5.2% of the N from leucaena and dactyladenia, respe ctively, while the two subsequent crops recovered <1%. The cowpea plan ts in the leucaena and dactyladenia microplots contained 0.5 and 1.1% of the residue N in the first harvest, Sixteen and 9% of the residue N was recovered by the leucaena hedgerow in the first and second prunin g following residue application. The dactyladenia hedges recovered max imally 3.1% of the residue N in a single pruning, The total N recovery in the leucaena microplots was approximate to 90% at 120 and 471 DAA, compared with 56 and 35% in the dactyladenia microplots. At 858 DAA, 62% of the added leucaena N was accounted for, compared with 25% of th e dactyladenia N. Residue quality was shown to have a major impact on the dynamics of applied residue N in alley cropping systems and will b e an important factor in deciding which residue-supplying plant specie s to integrate into similar cropping systems.