Integrated Plant Nutrient Management For Rice-Upland Crop Rotation System

Rotations of rice and other crops are practiced widely along the Yangtze River Basin where they occupy a total area of about 13 million hectares and they account for 30% of cereal crop production in China. However, a developing water crisis and environmental pollution arising from improper nutrient management threaten the sustainability of these crop rotations and a trend of declining or stagnating yields has been observed in the crop rotations. Improvements are therefore required in the management of nutrient resources, soil, water and straw.In the traditional approach to nutrient management in these crop rotations the objective was to attain maximum yield rather than optimize high yields and environmental protection. The emphasis was solely on fertilizer application, with no regard for the efficient utilization of indigenous nutrient or integration with other agricultural technologies. It also neglected the effects of alternate drying and wetting between the season of the associated crop and rice season on N utilization because of a limited understanding of N dynamics in these crop rotation systems. Non-flooded mulching cultivation is one promising solution to the shortage of irrigation water in rice-based cropping systems. However, detailed studies on productivity evaluation of non-flooded mulching cultivation in rice-wheat rotation systems, especially its long-term consequences, are not available and it is not known whether rice-wheat rotation systems are sustainable using non-flooded mulching cultivation.In the present study, three field experiments were carried out on the Chengdu Plain in southwest China. The aims were: 1) to understand how alternate drying and wetting between wheat and rice seasons affected the N cycling of the crop rotation; 2) to evaluate the productivity and sustainability of rice-wheat rotations under non-flooded mulching by using long-term experiments; and 3) to establish integrated plant nutrient management techniques combining cultivation, water saving, and no-tillage technology with nutrient management. The main results are summarized below.1. In rice-wheat rotation systems the mineral N in the top 60 or 80 cm of the soil profile after the wheat harvest increased with increasing N fertilizer application rate. On the other hand, the soil mineral N in the top of 60 or 80cm after the rice harvest, which was lower than that after the wheat season, was not been affected by N rate, rotation type or non-flooded mulching cultivation. In the present study, apparent N loss in the rice season accounted for 74 - 87% of total apparent N loss in the rice-wheat rotation. Compared to the treatment using conventional farming practice (Tra, representing one-third of the production area in the experimental region), integrated plant nutrient management (Opt) significantly decreased the apparent N loss in rice-wheat rotation systems and this was ascribed to decreased apparent N loss in the rice season. In conventional agricultural treatments, however, 50% N apparent loss in the rice season was derived from residual soil mineral N after the wheat harvest.2. Alternate drying and wetting between wheat and rice seasons (from drying to wetting) led to large losses of residual soil mineral N. In the conventional agricultural treatments, about 70% of the residual soil mineral N in the top 80 cm after the wheat season (125 kg ha'1) was lost from rice lowlands within 13 days of the flooding of aerobic soil. The loss of residual 15N fertilizer after the wheat seasonwithin 13 days of the flooding of aerobic soil accounted for 18% of total amount of residual N fertilizer after the wheat season, 58% of total loss of residual 15N fertilizer after the wheat season in rice season, and 10% of the total loss of residual soil mineral N during alternate drying and wetting stage. Integrated plant nutrient management significantly decreased residual soil mineral N and residual N fertilizer at 0-80cm soil depth after the wheat harvest, with subsequent significantly decreased N loss during the stage of alternate dryi...