Nutrient Uptake and Apparent Balances for Rice-Wheat Sequences. I. Nitrogen uri icon

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.

publication date

  • 2006
  • 2006