Effect of green manure rotation on soil fertility and organic carbon pool

Abstract: The area of fall-planted cover crop in China is quite low in paddy field, and multiple cropping index declines yearly, resulting in tremendous waste of soil resources. This reduction in fall-planted cover crop can lead to decrease in soil fertility. Most paddy field in southern China is suitable for growing winter green manure because of abundant light and heat resources. Winter green manure in general contains 15% - 20% of the organic matter. It can be used to improve soil nutrients cycling and facilitate the mineralization of soil organic matter. Comprehensive evaluation of green manures in different crop rotations in paddy fields of southern China region is needed in order to develop sustainable multiple cropping systems. The objective of this study was to determine the effect of green manure on different cropping systems (A: fallow-early rice-late rice→fallow-early rice-late rice (CK); B: milk vetch- rice- rice→rapeseed/peanut-rice; C: rapeseed/peanut- rice→ potato/maize+ soybean- rice; D: potato/maize+soybean- rice→vegetable/peanut+maize- rice; E: vegetable/peanut+maize- rice→milk vetch- rice- rice) on soil nutrients, soil organic carbon, and carbon pool management indexes in southern China where two rice crops per year were common. The experiment was conducted during September 2011 - November 2013. Soil samples (at depths of 10-20 cm) were taken after rice was harvested in 2013 for analysis. The results showed that compared with CK, green manure rotation treatments had significantly (P<0.05) improved organic matter, alkaline hydrolytic nitrogen and available potassium by 8.73%-15.59%, 11.79%-19.64%, and 5.80%-37.19%, respectively. Soil organic of green manure rotation treatments of B and C were 15.59% and 11.19% higher (P<0.05) than CK. Soil active organic carbon of all green manure rotation treatments was 29.03%, 19.96%, 16.67% and 21.75% respectively higher (P<0.05) than CK. Compared with CK, the soil carbon pool index significantly (P<0.05) increased by 15.70% for the treatment B, and soil carbon management index significantly (P<0.05) increased by 32.07 for the treatment B, 21.98 for the treatment C, 18.64 for the treatment D and 24.47 for the treatment E, respectively. Among the treatments, milk vetch- rice- rice→rapeseed/peanut- rice had the highest values for the soil carbon pool index and soil carbon management index. The soil organic matter and total nitrogen, available phosphorus, total organic carbon, active organic carbon, and carbon pool management index were highly significantly (P<0.01) correlated. Soil total nitrogen, alkaline hydrolytic nitrogen, and available phosphorus had a significant (P<0.05) correlation with carbon pool management index. In addition, soil organic carbon was significantly (P<0.05) positively correlated with active organic carbon and carbon pool management indexes. Therefore, green manure rotation, especially milk vetch- rice- rice→rapeseed/peanut- rice could increase soil organic carbon contents and soil carbon pool management index, improve soil quality and soil fertility under the local soil fertility conditions, and was important for promoting sustainable development of agriculture.