Wheat-maize-rice cropping on permanent raised beds in Bangladesh

摘要

Rice-wheat (RW) cropping systems are critical to food security of the increasing population in Bangladesh. However, the sustainability of RW systems is threatened by productivity decline and environmental sustainability. Crop production on permanent raised beds (PRB) is expanding worldwide as a way to increase system productivity, diversify cropping and improve the efficiency of resource use, especially water. When coupled with raised beds, straw retention can improve soil moisture retention, soil health and crop productivity. A 3-year study was conducted at the Wheat Research Centre, Dinajpur, Bangladesh, to compare the effects of fourN fertiliser rates (0%, 50%, 100% and 150% of the recommended rate) and four straw retention (SR) / tillage treatments (100% SR of all crops + permanent raised beds (PRB), 50% SR + PRB, 0% SR + PRB and 0% SR + conventional tillage on the flat (CTF)) in a RW-maize cropping system. Permanent beds with straw retention produced the highest grain yields for all three crops in the sequence. Within each N rate the total system (rice+wheat+maize) productivity was greatest with 50-100% SR on PRB and least in CTF with zero straw retention. At 100% of recommended fertiliser N rate, mean annual system productivity was 17.9-19.7 t/ha for PRB with 50-100% SR, 15.7 t/ha with PRB without SR and 14.1 t/ha with CTF without straw. For all three crops, yields of PRB with 50% and 100% SR were similar. These benefits from straw retention with PRB were established within 2-3 years. Yield in N-unfertilised plots increased when straw was retained due to increased supply and uptake of N. The results suggest that N fertiliser rates can be reduced when straw is retained. Soil organic matter in surface soil layers of the PRB had increased by 13-41% after 4 years (ie four rice+wheat+maize crop cycles) with straw retention, with a greater increase with 100% SR than 50% SR. Soil organic C in PRB without SR was similar to the initial organic C prior to bed formation. Straw retention is an important component of soil management and may have long-term positive impacts on soil quality. Compared with conventional tillage on the flat with all crop residues removed, the combination of PRB with residues retained appears to be a very promising technology for sustainable intensification of RW systems in Bangladesh.