Crop Productivity, Soil Nitrogen And Phosphorus Forms And Nutrient Losses In Different Multiple Cropping Systems On Slope Land

Danjiangkou Reservoir is the water source of the middle line of South-to-North Water Transfer Project in China. In Danjiangkou Reservoir catchment area, a traditional mountainous farming region, the agricultural non-point source pollution is increasingly serious recently, which may lead water quality develop into eutrophic state in Danjiangkou Reservoir. In this study,3-year duration field experiments were conducted to test the differences in crop productivity and nutrient absorption, runoff production and soil erosion and nutrient losses of nitrogen, phosphorus and potassium from slope farmland of different multiple cropping patterns, combined with the main crops, under different fertilizer supplies in this area. Meanwhile, the effects on nitrogen and phosphorus losses of the changes in the forms of soil nitrogen and phosphorus were analyzed. The purpose of the present study is to provide a theoretical and technological support for controlling agricultural non-point source pollution from source emergence in this area. The main results were as follows:(1) Under farmer’s fertilization, both economic and straw yields were higher in wheat plantation than that in rape plantation on slope farmland in winter cropping season. In summer cropping season, maize plantation got higher productivity including economic and straw yields than sweet potato plantation. Higher fertilizer application could improve economic and straw yields, and nutrient absorptions of crops significantly, on the basis of current farmer’s fertilization level, only with an exception of sweet potato plantation.(2) Runoff production and soil erosion from farmland changed with seasonal rainfall amount, crop plantations and fertilizations, and etc. Under different fertilizer supplies, total runoff production and soil erosion were highest in the continuous multi-cropping system of wheat-sweet potato pattern, but they were lower in wheat-maize compared to other plantation patterns. Increasing fertilizer supplies could reduce runoff production and soil erosion to different degrees, from slope farmland.(3) Under farmer’s fertilization, the total amount of nitrogen, phosphorus and potassium losses from the slope farmland were highest in wheat-sweet potato pattern, but they were lower in rape-maize and wheat-maize patterns. Under higher fertilization, the amount of total phosphorus (TP) loss showed an increase trend but total nitrogen (TN) and dissolved potassium (DTK) loss decreased in rape-maize pattern. The amount of TN and DTK losses increased but TP loss decreased in wheat-sweet potato pattern, while, TN and TP losses increased but DTK loss decreased in wheat-maize pattern under higher fertilization, compared to farmer’s fertilization.(4) After a3-year duration trial, soil nutrient contents increased to different degrees in various continuous multi-cropping systems, specifically with a higher increasing rate under higher fertilization than farmer’s fertilization. Ca10-P accounted for the largest proportion of soil inorganic phosphorus and Ca2-P was the lowest. The content of available P had significantly positive correlations with the contents of Ca2-P, Al-P, Fe-P and O-Al-P, respectively, in soil. Along with crop growth and development, the contents of available P and Ca10-P changed continuously in soil, and O-Fe-P might be the transitional form in their changes.(5) Nutrient losses from farmland were related closely to the changes in nutrient contents in soil of continuous multi-cropping systems. There was a significantly positive correlation between the concentration in runoff and the content in soil for nitrate nitrogen and ammonium nitrogen, respectively. The concentrations of TP, DTP and Orthophosphate phosphorus in runoff were significantly positively correlated with the contents of available P, Ca2-P, Al-P, Fe-P, O-Al-P, but significantly negatively correlated with the contents of O-Fe-P and Ca10-P in soil, respectively.(6) In the various multiple intercropping systems, the higher total straw yield and higher wheat yield were obtained in wheat//pea pattern than in wheat//vicia faba pattern in winter cropping season; while, the higher maize yield was obtained in maize//soybean but higher total straw yield in maize//sweet potato. However, the total biomass production was lower in intercropping systems than that in monoculture pattern.(7) The total runoff production and soil erosion and the nutrient losses of nitrogen, phosphorus and potassium from farmland showed decrease trends in different multiple intercropping patterns than in monoculture pattern under farmer’s fertilization. Compared between multiple intercropping patterns, the total runoff production and soil erosion and TN loss from farmland were lower in wheat//pea-maize//soybean system than in wheat//vicia faba-maize//sweet potato, while, the TP and DTK losses were lower in the latter than in the former, but without significant difference.(8) From the present study, the best environment-friendly pattern for continuous multi-cropping is wheat-maize, followed by rape-maize pattern, the two multiple intercropping patterns was better than wheat-maize pattern in Danjiangkou Reservoir area. However, increasing fertilization may increase the risks of N and P leakage in wheat-maize pattern and P leakage from farmland in rape-maize pattern.