Recovery of leucaena and dactyladenia residue nitrogen-15 in alley cropping systems

Quantification of the fate of residue N is essential in low-input tropical cropping systems for the development of management practices that optimize N-use efficiency. The recovery of N from N-15-labeled leucaena [Leucaena leucocephala (Lam.) de Wit] and dactyladenia [Dactyladenia barteri (Hook f ex Oliv.) Engl.] leaf residues was followed in the soil, crop, and hedgerow of the respective alley cropping systems during 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, respectively, while the two subsequent crops recovered <1%. The cowpea plants 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 pruning following residue application. The dactyladenia hedges recovered maximally 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 the dactyladenia N. Residue quality was shown to have a major impact on the dynamics of applied residue N in alley cropping systems and will be an important factor in deciding which residue-supplying plant species to integrate into similar cropping systems.