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

The majority of field controlled-release urea (CRU) experiments conducted on maize in recent years were arranged in north China where 80% of maize in China is grown. In 2011, a field experiment was carried out in Yunnan, a big maize producer in south China, to investigate performance of CRU in a high fertility sloping land soil under plastic mulch in humid climate with irregular drought spells in summer. The experiment included four N rates (0, 105, 157.5, and 210 kg N/ha) replicated three times. Each rate of N was tested as paired CRU and regular urea (RU) treatments for strict comparison of CRU effect. Two split N treatments were also included, one with 40% RU basal at seeding and 60% as a top-dressing 53 days after seeding, compared with 40% RU and 60% CRU both applied basal at seeding. All treatments received equal rates of P and K fertilizers that were used as basal application.

Results indicated that all the CRU treatments produced higher maize yields compared to its counterpart RU treatments. The yield increase, however, was not statistically significant, except the CRU versus RU at the full N rate (210 kg N/ha). Maize yields were increased with an increase in N rates and leveled off at 157.5 kg N/ha for RU and at 105 kg N/ha (50% of the full N rate) for CRU. Agronomic efficiency of both CRU and RU decreased with increasing increments of N application, ranging from 9.5 to 12.6 kg kernels/kg N for CRU and 3.1 to 8.4 kg kernels/kg N for RU. Nevertheless, some of the CRU granules remained intact or with partial N release at harvest time due to protection of the plastic mulch on the soil surface from rainwater infiltration, resulting in inefficient use of CRU by maize and underestimated maize response. Thus, even in this humid climate, the right method of CRU placement needs further study to safeguard complete N release from the coating during the maize growing season. Yunnan-BFDP-11