Nutrient losses from sloping lands and its control in Sichuan
IPNI-2006-CHN-SC23
09 Jan 2009
2008 Annual Interpretive Summary
Nutrient Losses from Sloping Lands as Affected by Rain Intensity and Fertilizer Placement in Sichuan, 2008
This project continues to address nutrient management on crops grown on Sichuan’s sloping farmlands during the summer rainy season. The objectives were to: 1) identify the major course of applied nutrients lost to waters under different rain intensities and cropping patterns; 2) determine the effect of fertilizer rates and rainfall intensities on nutrient losses; and 3) study the best nutrient management measures needed to overcome the problem. In 2006 and 2007, the major course of nutrient loss under different rain intensities, cropping patterns, and fertilizers were identified. In 2008, the project began to assess the effect of rain intensity and different N fertilizer placement methods–one basal application (CK), split application with irrigation (SAI), or split application without irrigation (SANO) at ear development–on nutrient loss.
Results showed that fertilizer placement considerably affected not only growth and yield of corn, but also soil erosion and nutrient losses. Compared to a single, basal N application representing common farm practice, land coverage by standing corn increased by 12% with SAI and by 6% with SANO. Similarly, corn yield increased by 7% with SAI and by 5% with SANO. Soil loss was reduced by 80 kg/ha with SAI, but increased by 130 kg/ha with SANO. Why the SANO treatment increased soil erosion is still unclear.
Regardless of fertilizer placement, P and K losses through soil erosion and runoff were generally increased with increased rainfall intensity. For N, however, there was no clear trend observed. Through runoff, N loss was highest and ranged between 9.6 kg/ha in the CK and 8.2 kg/ha for the SAI treatment. Loss of K was similar across treatments, ranging between 3.3 kg/ha for SAI and CK to 3.7 kg/ha for the SANO treatment. Phosphorus loss was marginal at only 0.1 kg/ha across treatments. More than 96% of N and 72% of K were lost through leaching.
Nitrogen placement affects N loss considerably and splitting N application with irrigation at ear development can effectively reduce N loss to groundwaters. Phosphorus loss from fertilizers applied to the sloping lands is minor and cannot be blamed as a major pollution source for water eutrophication. Sichuan-06B