Multiseason recoveries of organic and inorganic nitrogen-15 in tropical cropping systems

• Main Authors: Dourado Neto, Durval, Powlson, David S., Abu Bakar, Mohd Rizam, Bacchi, Osny Oliveira Santos, Basanta, Maria del Valle, Cong, Phan Thi, Keerthisingh, Gamini, Ismaili, Mohammed, Rahman, Mohammad Saidur, Reichardt, Klaus, Safwat, Mohamed Said Ali, Sangakkara, Ravi, Timm, Luis Carlos, Wang, Jia Yu, Zagal, Erick, Van Kessel, Chris
• Format: Article
• Language: English; English
• Published: 2009
• Online Access: http://psasir.upm.edu.my/id/eprint/4778/1/Multiseason%20recoveries%20of%20organic%20and%20inorganic%20nitrogen.pdf; http://psasir.upm.edu.my/id/eprint/4778/; http://dx.doi.org/10.2136/sssaj2009.0192

In tropical agroecosystems, limited N availability remains a major impediment to increasing yield. A 15N-recovery experiment was conducted in 13 diverse tropical agroecosystems. The objectives were to determine the total recovery of one single 15N 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 duringthe first growing season was derived from fertilizer. On average, 79% of crop N was derived from the soil. When 15N-labeled residues were applied, in the first growing season 4% of crop N was derived from the residues. Average recoveries of 15N- 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 15N 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 15N-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 N losses, management practices to improve N use efficiency and reduce losses in wet tropical regions will remain a challenge.