Effects of intercropping and waxy maize stalk returning on distribution of soil aggregate and soil organic carbon in broccoli continuous cropping filed

Abstract: With the large-scale and intensive development of vegetable planting, continuous cropping obstacles have become more and more serious. Intercropping farming and straw returning have great values for improving soil ecological environment in vegetable fields. The objective of this study was to evaluate the changes of soil water-stable aggregate distribution and stability after 6 years in response to long-term relay-intercropping and crop straw management experiment in broccoli and waxy maize cropping system. Three treatments were used: relay-intercropping mode of broccoli and waxy maize with waxy maize straw returning (B/MR-B), relay-intercropping mode of broccoli and waxy maize without waxy maize straw returning (B/M-B) and broccoli continuous cropping (B-B). As a result, the size class of soil water-stable aggregate decreased with the soil layers deepening, while the distribution range was concentrated. The main ranges in seedlingperiod and ball-flower growth period were 0.25-0.5 mm and <0.25 mm size classes. In vegetative period, the main ranges were 0.5-1 mm and 0.25-0.5 mm size classes. While in vegetable harvest period, the main ranges were 0.5-1 mm, 0.25-0.5 mm and <0.25 mm size classes. The size classes of 0.5-1 mm and 0.25-0.5 mm in B-B treatment were lower than in other treatments. On the contrary, the size classes of <0.25 mm in B-B treatment were significantly higher than in other treatments. During whole growth period of broccoli, the water-stable macro-aggregate followed by B/MR-B>B/M-B>B-B. Relay-intercropping with straw returning significantly increased the content of the soil organic carbon (SOC). Meanwhile，the water-stable macro-aggregate was also correlated with the SOC content according to the multiple regression analysis. The water-stable macro-aggregate was extremely significantly positively correlations with SOC in the 0-10 cm and 10-20 cm layers (P<0.01). In the 20-40 cm layers, the water-stable macro-aggregate were significantly positively correlations with SOC (P<0.05). Our findings indicated that relay-intercropping with straw returning increases the proportion of water-stability aggregate, improves soil physical and chemical properties and reduces continuous cropping obstacles.