摘要：

A 3 year field experiment was conducted to study the productivity, soil fertility and N-use efficiency of intensified Rice-Wheat (R-W) systems by adding a third pre-rice crop of mungbean. System productivity, fertility and N use efficiency were evaluated under five N fertilizer levels (0, 50,100,150 and 200 % N of recommended dose, two straw retention (SR) levels (0 and 100%) and two tillage options (permanent raised bed and conventional tillage with planting on the flat (CTP) in a R-W- mungbean cropping system. Permanent beds with straw retention produced the highest productivity for all three crops in the sequence. Within each N rate the total system (rice-wheat-mungbean) productivity was greatest with 100% SR on PRB and least in CTP with no straw retention. At 100% of recommended fertilizer N rate, mean annual system productivity was 12.5 t/ha for PRB with 100% SR, 11.2 t/ha with PRB without SR and 10.3 t/ha with CTP without SR. N uptake and use efficiency were increased with increasing N levels with bed planting up to 150% N application (150 kg N ha-1) in wheat, 100% (80 kg N ha-1) in rice and 100% N (20 kg N ha-1 ) in mungbean for all three years. System productivity in N unfertilized plots increased when straw was retained due to increased supply and uptake of N. The results suggest that N fertilizer rates may be reduced when straw is retained. Soil organic matter in surface soil layers of the PRB had increased by 0.22% after 3 years (3 rice-wheat-mungbean crop cycles) with straw retention, with a greater increase with 100% SR. Straw retention is an important component of soil management and may have long term positive impacts on soil quality. Compared with conventional tillage with crop residues removed, the combination of PRB with nitrogen and residues retained appears to be a very promising technology for sustainable intensification of R-W systems in Bangladesh

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