Effects of poplar agroforestry systems on soil nutrient and enzyme activity in the coastal region of eastern China

PurposeTo understand the effects of poplar-intercropping systems on soil nutrients and soil enzyme activities, and further analyzed the relationship between soil enzyme activities and soil nutrients.MethodsThree different planting systems were chosen: a monoculture wheat (Triticum aestivum) system (W), a narrowly spaced poplar (Populus deltoides)-wheat intercropping system (PWN), and a widely spaced poplar-wheat intercropping system (PWW). The chemical properties (soil organic matter (SOM), total nitrogen (TN), total phosphorus (TP), total potassium (TK), available nitrogen (AN), available phosphorus (AP) and available potassium (AK)) and four enzymatic activities (urease, catalase, sucrase and alkaline phosphatase) in four soil layers (0-20, 20-40, 40-60 and 60-100 cm) of two sampling sites (1.5 and 3.5 m from tree row) in the three planting systems were investigated.ResultsThe SOM, TN, TP, TK, AP, AK concentrations and four soil enzyme activities were higher in the intercropping systems than in the monoculture wheat system, especially the PWN system. In the vertical direction, the soil nutrient concentrations and soil enzyme activities decreased with soil depth (P < 0.001), except AK and catalase. In the horizontal direction, the SOM, TN, TP, TK concentrations and four soil enzyme activities decreased with greater of distance from the poplar row, but the distribution trend was the opposite for AN, AP and AK. The correlation analysis revealed that the soil enzyme activities were significantly correlated with the SOM, TN, TP, AN and AP concentrations in the three planting systems (P < 0.01).ConclusionIn conclusion, agroforestry systems can significantly increase soil nutrient status and soil enzyme activities and can be an efficient method for improving soil health conditions. Additionally, compared with the wide poplar spacing in the intercropping system, the reasonably dense planting of intercropped poplar had more obvious effects on improving soil enzyme activities and soil nutrients.