Effects of intercropping Stylosanthes guianensis as a green manure on the soil fertility of coconut plantations

To investigate the effect of intercropping Stylosanthes guianensia green manure (GM) on the soil fertility of a coconut plantation and provide theoretical reference support for intercropping and rationally applying GM in coconut plantations with acidic soil. Effects of different Stylosanthes GM utilization patterns on the soil fertility of a coconut plantation were studied in a three-year field experiment. The three treatments included a single coconut tree without intercropping GM, intercropping Stylosanthes with GM mulch utilization, and intercropping Stylosanthes with GM utilization, and they were designed to observe the dynamics of soil fertility indexes, including the soil organic matter, mineral nutrients, and pH in cultivated soil layers. GM could effectively increase the content of soil organic matter and mineral nutrients and improve the soil acidity. After the GM treatment, the content of soil organic matter, alkali-hydrolyzed nitrogen, available phosphorus, available potassium, soil available iron, available manganese, available copper, available zinc, and pH increased by 54.9%, 62.3%, 150.4%, 53.3%, 72.3%, 82.8%, 22.1%, 19.1%, and 10.9%, respectively (P < 0.05). After the GM mulch treatment, the content of organic matter, alkali-hydrolyzed nitrogen, available phosphorus, available potassium, available iron, available manganese, available zinc, and pH increased by 28.3%, 37.5%, 89.4%, 39.3%, 39.1%, 39.5%, 19.1%, and 6.9%, respectively (P < 0.05). The content of organic matter, alkali-hydrolyzed nitrogen, available phosphorus, available iron, available manganese, available copper, and available zinc in the GM treatment was 20.7%, 18.0%, 32.3%, 23.8%, 31.1%, 10.7%, and 7.7% higher (P < 0.05) than that of the GM mulch treatment over three years. GM could increase the content of mineral nutrients in the first year after manuring and effectively improve the soil acidity and pH after three years (P < 0.05). GM mulch significantly increased the content of soil organic matter, available nitrogen, available phosphorus, available manganese, available copper, and pH in the second year (P < 0.05). GM intercropping with Stylosanthes could significantly improve the soil fertility in the coconut plantation, and the effect of GM was better than that of GM mulch.