Response of Maize under Plastic Mulch to Controlled Release Urea in Yunnan

This research project was initiated in Yunnan province in 2011 to investigate the performance of controlled release urea (CRU) in a high fertility sloping land soil under plastic mulch in humid climate with irregular drought spells in summer. In 2011, because CRU granules were placed too close to the soil surface at seeding time, it resulted in some of the CRU granules remaining intact or with partially N release even at harvest time due to the protection of plastic mulch on soil surface from rainwater infiltration. This year, the CRU placement was done at 5 cm below the soil surface. The experiment included four N rates (0, 120, 180, and 240 kg N/ha) replicated three times. Each rate of N was tested with paired CRU and regular urea (RU) for strict comparison of CRU effect. Besides, one treatment with 40:60 of RU split application (i.e. 40% basal application at seeding and 60% as a top-dressing 63 days after seeding) was compared with another treatment of 40:60 of RU:CRU applied as one basal application at seeding. All treatments received equal rates of P and K fertilizers that were applied basally.

Similar to the results obtained in 2011, all CRU treatments, with the exception of RU split application, produced significantly higher maize yields compared to RU treatments. Maize yields were increased with an increase in N rates, but leveled off at 180 kg N/ha (i.e. 75% of the full N rate) for both RU and CRU. Thus, the highest maize yield was obtained at 75% of full rate CRU, which was 886 kg/ha (8%) higher than the yield with RU treatment (180 kg/ha). Different from the results in 2011, the 40:60 RU split application treatment produced maize yields similar to 40:60 CRU split application treatment. Agronomic efficiency of both CRU and RU treatments decreased with increase in N application, ranging from 7.7 to 13 kg kernels/kg N for CRU and 6.5 to 8.6 kg kernels/kg N for RU. With the increase in CRU placement depth, maize yield was improved as compared to in 2011, and the N release from coated urea granules was verified to be more complete at maize harvest. Yunnan-BFDP-2011