Nutrient losses from sloping lands and its control in Sichuan
IPNI-2006-CHN-SC23
04 Feb 2008
2007 Annual Interpretive Summary
Nutrient Losses from Sloping Lands in Sichuan as Affected by Rainfall Intensity and Fertilizer Rates, 2007
This project has addressed nutrient management on sloping farmlands during the summer rainy season since 2006. In recent years, nutrient losses through soil run-off and leaching, and non-point environmental pollution sources to both surface and underground waters, have become an increasing societal concern. However, how and what proportion of applied nutrients are transported from the sloping lands to water sources is not well understood. The objectives of this project 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 different fertilizer rates and rain intensities on nutrient losses, and (3) study the best nutrient management measures to overcome the problem. In 2006, the major course of applied nutrients lost to the waters under different rain intensities and cropping patterns was identified. In 2007, the focus was on determining the effect of different fertilizers and rain intensities on nutrient losses.
Amounts of soil erosion and run-off from sloping lands were highly positively correlated with rain intensity. Fertilizer application played a dual role on both soil erosion and nutrient losses. Balanced fertilization (BF) usually promoted maize growth and maximized crop coverage which effectively intercepted raindrops and protected soil from erosion. Compared to the BF treatment of 300-150-150 kg N-P2O5-K2O/ha, the farmer practice (FP) of applying 300-150-0 kg/ha had 3 to 6% less maize coverage, 500 kg/ha more soil erosion, and 12 mm more run-off during in a single rainfall event. Researchers tested a higher N rate of 450 kg/ha along with the same P and K rates, but this also resulted in 2 to 5% less maize coverage, 450 kg/ha more soil erosion, and 9 mm more run-off compared to the BF.
Amounts of P and K lost through soil erosion and run-off generally increased with rainfall intensity. However, there was no clear trend observed for N in relation to rainfall intensity. Under any rainfall intensity, the BF treatment was remarkably effective at reducing NPK losses compared to the FP or the treatment supplying extra N. Though N is most susceptible to leaching losses, the amounts lost through run-off and leaching accounted for only about 7.6 kg/ha or 2.5% of the total N fertilizer application. For available P, losses represented less than 0.02% of the total P fertilizer application. These data further substantiated that N and P lost from fertilizers applied to sloping lands cannot be blamed as the major N and P contributors for water pollution. Sichuan-BFDP-06