Nutrient losses from sloping lands and its control in Sichuan
IPNI-2006-CHN-SC23
30 Jan 2007
2006 Annual Interpretive Summary
Nutrient Losses from Sloping Lands as Affected by Rain Intensity and Cropping Patterns in Sichuan, 2006
Nutrient losses through soil runoff and leaching are blamed for non-point environment pollution of surface water and groundwater, and this issue has become a major societal concern. However, how and what proportions of applied nutrients are being transported from 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 the 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 the first year, the experiment consisted of three cropping patterns including down slope cultivation, contour ridge cultivation, and flat cultivation, and three artificial rain intensities providing small (0.972 mm/min for 62 min), medium (1.741 mm/min for 34.5 min), and heavy (2.255 mm/min for 26.6 min) rainfall events. Rains occurred soon after each fertilizer application. One NPK fertilizer rate was used for all treatments. Corn, one of the most common summer crops grown on sloping lands in southwest China, was employed in the experiment.
The amounts of soil eroded and runoff from the sloping lands were highly correlated with rain intensity and cropping patterns. Contour cultivation was highly effective in soil conservation, while flat cultivation was highly prone to soil erosion and runoff. Leaching was negatively correlated with rain intensity, and ranged from 48 L/plot under heavy rains to 56 L/plot under small rains. The effect of cropping pattern on leaching was inversely correlated to its effect on surface runoff. Total amounts of available soil N removed from sloping lands in water portions (runoff + leaching) were 3.64, 3.18 and 3.69 kg/ha under heavy rains; 3.28, 3.51, and 2.78 kg/ha under medium rains; and 2.48, 4.98, and 3.64 kg/ha under small rains for downslope cultivation, contour cultivation and flat cultivation, respectively. Leaching provided the major pathway for available N loss, and accounted for 64 to 88% of total available N loss under heavy rains, 78 to 98% under medium rains, and 98 to 100% under small rains. Amounts of P lost through leaching were very minor, ranging from 0 to 0.04 kg P/ha regardless of the rain intensity or cropping pattern.
Though N is most susceptible to leaching losses, the amounts lost due to runoff and leaching accounted for only about 1% of fertilizer N application (i.e., 300 kg N/ha). For available P, losses represented less than 0.1% of P fertilizer application (i.e., 150 kg P2O5/ha). Nitrogen and P loss from fertilizer application to sloping lands cannot be blamed for major N and P contributions to water pollution. Sichuan-BFDP-06