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Multiseason Recoveries of Organic and Inorganic Nitrogen‐15 in Tropical Cropping Systems

2010; Wiley; Volume: 74; Issue: 1 Linguagem: Inglês

10.2136/sssaj2009.0192

1435-0661

Durval Dourado Neto, D. S. Powlson, Rosenani Abu Bakar, Osny Oliveira Santos Bacchi, María Basanta, Phan Thi Cong, G. Keerthisinghe, Mohammed Ismaili, Shakilur Rahman, Klaus Reichardt, M. S. A. Safwat, Ravi Sangakkara, Luís Carlos Timm, J. Y. Wang, Erick Zagal, Chris van Kessel,

Phosphorus and nutrient management

In tropical agroecosystems, limited N availability remains a major impediment to increasing yield. A 15 N‐recovery experiment was conducted in 13 diverse tropical agroecosystems. The objectives were to determine the total recovery of one single 15 N application of inorganic or organic N during three to six growing seasons and to establish whether the losses of N are governed by universal principles. Between 7 and 58% (average of 21%) of crop N uptake during the first growing season was derived from fertilizer. On average, 79% of crop N was derived from the soil. When 15 N‐labeled residues were applied, in the first growing season 4% of crop N was derived from the residues. Average recoveries of 15 N‐labeled fertilizer and residue in crops after the first growing season were 33 and 7%, respectively. Corresponding recoveries in the soil were 38 and 71%. An additional 6% of the fertilizer and 9.1% of the residue was recovered by crops during subsequent growing seasons. There were no significant differences in total 15 N recovery (average 54%) between N from fertilizer and N from residue. After five growing seasons, more residue N (40%) than fertilizer N (18%) was recovered in the soil, better sustaining the soil organic matter N content. Long‐term total recoveries of 15 N‐labeled fertilizer or residue in the crop and soil were similar. Soil N remained the primary source of N for crops. As higher rainfall and temperature tend to cause higher 15 N losses, management practices to improve N use efficiency and reduce losses in wet tropical regions will remain a challenge.