Effects of Returning Green Manure-Chinese Milk Vetch on the Availability and Transformation of Zinc in Purple Tidal Mud Soil under Rice Cultivation

This study aimed to investigate the impact of different levels of Chinese milk vetch (Astragalus sinicus L.) incorporation on the availability and transformation of zinc in purple tidal mud soil under rice cultivation. A two-year pot experiment was conducted, comprising seven treatments: a control group without fertilizer, a control group with Chinese milk vetch application, a control group with chemical fertilizer application, and four treatment groups with varying levels of Chinese milk vetch application following chemical fertilizer application. Results showed that Chinese milk vetch application increased the content of available zinc (DTPA-Zn) in purple tidal mud soil. Sole application of Chinese milk vetch ultimately enhanced the transfer factor of zinc in purple tidal mud soil and reduced the distribution index. However, applying Chinese milk vetch after chemical fertilizer application ultimately decreased the transfer factor of zinc and increased the distribution index. Furthermore, sole application of Chinese milk vetch facilitated the conversion of zinc in purple tidal mud soil into available forms, while applying it after chemical fertilizer application promoted the transformation of zinc into ineffective forms, with a greater conversion observed at higher levels of Chinese milk vetch application.