Effect of release controlled urea on rice yield and N use efficiency in Sichuan basin


03 Feb 2011

2010 Annual Interpretive Summary

Effect of Controlled-Release Urea on Rice Yield and Nitrogen Use Efficiency in the Sichuan Basin, 2010

The objective of this field experiment was to continue evaluating the effect of controlled-release urea (CRU) applied at rice transplanting to regular/bare urea (RU) split at rice transplanting and tillering stage. The deliverables from the project will be data on the impact of CRU on crop yield, N uptake, and economic benefit. The field experiment in 2010 was conducted on a medium to low fertility soil using 0, 75, 112.5, and 150 kg N/ha. Each rate of N was tested with paired CRU and RU treatments. Besides, a RU treatment using a 40:60 split between a basal application at rice transplanting and a top-dressing at tillering stage was compared with a 40:60 split of RU:CRU applied as one basal application at rice transplanting. All treatments received equal rates of basally applied P and K fertilizers.

Results showed that at the same N rate, the CRU treatment always produced much higher or significantly higher rice grain yield than the RU treatments. The 100% CRU produced the highest rice yield among all the treatments, which was followed by the 40:60 split of RU:CRU. Any treatment receiving N rates less than 150 kg/ha significantly reduced rice yield compared to 100% RU. This differed from the results obtained in 2008 and 2009 when 75% CRU produced equivalent or even high rice yields than the 100% RU treatment. By scrutinizing the data obtained from the CRU trials to date, discrepancies to date could be mainly attributed to soil fertility, that is, the fertility of soils selected in 2008 and 2009 were high to medium-high, but medium-low in 2010. Thus, in the low fertility soils, reduced N rate can be a risk to rice yields, even for CRU. Besides, the unusual low temperatures that occurred in the spring and early summer of 2010 may also have affected the normal behavior of CRU and thus the rice growth.

All the CRU treatments significantly improved N use efficiency by 8 to 22 % and agronomic efficiency by 4 to 8 kg grain/kg N compared with its counterpart RU treatments. Thus, CRU can be a good substitute that can improve rice yield while reducing the risk of N loss to the environment. Sichuan-BFDP-08