Effects of the reduction of controlled-release urea application on nitrogen leaching in double cropping paddy field.

Nitrogen (N) leaching is a major pathway of N losses in paddy fields. Here, an experiment was conducted to assess the effects of the reduction of controlled-release urea application on grain yield and N leaching in a double-cropping paddy field. Fertilization treatments included zero-N (CK, control, 0 kg N·hm-2), conventional urea (CU, 180 kg N·hm-2), and four polymer-coated urea fertilization levels, i.e., 1.0CRU, 0.9CRU, 0.8CRU, 0.7CRU, which represented 0, 10%, 20% and 30% reduction of fertilizer inputs relative to CU, respectively. Leachate was collected at the soil depth of 60 cm using field leakage pool method. Nitrogen leaching peaked shortly after fertilization, implying that measures should be taken to prevent N leaching in the early period. Nitrogen losses from leaching were 42.3 kg N·hm-2 for 0.8CRU, and by 37.7 kg N·hm-2 for 0.7CRU, significantly lower than the leaching in CU (53.9 kg N·hm-2). Nitrogen leaching in 0.7CRU was significantly lower than that in 1.0CRU (51.3 kg N·hm-2). 11.9%-13.5% of the fertilizer N was lost via leaching across the six treatments with comparable N loss rates. Rice yields, N utilization efficiency and N harvest index were significantly higher in 0.8CRU and 0.7CRU relative to CU. Our findings suggested that the use of CRU would permit a reduction in N application by 20%-30%, which could maintain the rice yield and obtain a reduction in N leaching.

[Changes of heavy metals form during aerobic high temperature composting of pig manure and the effects of passivators].

Sequential extraction method was employed to study the heavy metals concentration and form change during aerobic high temperature compositing of pig manure, and the effects of amendment with different proportion of passivators on the concentration and form change. During the composting process, the concentrations of total As, Cu, and Zn in the manure all increased to some extent. As for the form change of the heavy metals, the exchangeable As and Zn decreased while the residual As and Zn increased, indicating that the availability of As and Zn declined through the composting process. On the other hand, the exchangeable and residual Cu decreased while the carbonate-, Fe/Mn-, and organic bound Cu increased, suggesting the potential environmental risk of the future application of the compost. Among the passivators amended, 5.0% of sepiolite and 2.5% of bentonite had the best effect in reducing the availability of As and Zn, with the residual form of As and Zn after composting increased by 79.8% and 158.6%, respectively, and 7.5% of sepiolite induced the least decrement (39.3%) of residual Cu, compared with the control. Therefore, amendment with appropriate proportion of passivator during pig manure composting could decrease the availability of heavy metals in the manure, and reduce the environmental risk of applying the compost to farmland.