Nutrient Uptake and Apparent Balances for Rice-Wheat Sequences. I. Nitrogen |
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| Authors: | J Timsina G M Panaullah M A Saleque M Ishaque A B M B U Pathan M A Quayyum |
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| Institution: | 1. School of Agriculture and Food Systems , The University of Melbourne , Victoria, Australia;2. Soil Science Division , Bangladesh Rice Research Institute , Bangladesh;3. Agronomy Division , Bangladesh Agricultural Research Institute , Bangladesh |
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| Abstract: | ABSTRACT Nitrogen (N) nutrition of the rice-wheat (RW) systems of the Indo-Gangetic Plain is important for sustaining the region's productivity and food needs. Soil N plays an important role in regulating the supply of N to plants. Monitoring plant concentrations, uptake, and balance of N assist in our understanding of plant and soil N status and in devising N-fertilizer strategies for both individual crops and a cropping system. Field experiments with rice-wheat-mungbean and rice-wheat-maize annual cropping sequences were conducted at Joydebpur, Nashipur, and Ishwordi in Bangladesh, which differ in their soils and climates. The experiments compared three pre-rice treatments (mungbean residues retained, mungbean residues removed, and maize residues removed), supplying each with two fertilizer levels (soil-test based, or STB, and farmers' practice, or FP). Zero N (control) treatments were included, with all other nutrients applied as STB or FP. The objectives were to detect N deficiency, if any, in the component crops, and to determine the changes in soil N fertility, plant N uptake, and soil N balance for various RW sequences. There was a significant decrease in mineral N in the topsoil (0–15 cm) of the +N mungbean and maize-residues removed treatments at Ishwordi, and a generally significant but less marked decline under the same treatments at Nashipur. Wheat and maize crops suffered from N deficiency ranging from 33% to 95% each year, at all sites, but deficiency in rice and mungbean was minimal. Annual system-level N uptake across sites ranged from 89 kg ha?1 for the control to 239 kg ha?1 for sequences containing maize with N. There were significant linear relationships between total system productivity (TSP) and annual N application and between TSP and annual system-level N uptake. Considering no N loss through the system, N fertilizer resulted in a positive N balance that ranged between 24–190 kg ha?1 compared with a negative balance of between 40–49 kg ha?1 without it. However, if a 30% N loss was assumed, N balances were reduced to between ?37–62 kg/ha?1 for N-containing treatments, and to between ?64–55 kg/ha?1 for the control treatments. Further research is needed to understand N depletion and replenishment and to sustain the productivity of the RW system. |
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| Keywords: | N concentration n uptake apparent n balance rice-wheat-mungbean ricewheat-maize |
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