Effects of earthworm tillage on soil nutrients and enzyme activities in vegetable fields

Long-term positioning experimental plots were carried out to study the effects of biological tillage on soil nutrients and enzyme activities of vegetable fields in west of Chongming Island, Shanghai. After three continuous years of the study, the results show that the contents of soil nutrients under the biological tillage are significantly higher than those of the no-tillage, the highest increasing rates of 182.2%, 174.5% and 133.2% in soil organic matter, total nitrogen, total phosphorus, and the highest increasing rates of 125.0%, 432.5% and 21.3% in soil available nitrogen, available phosphorus and potassium. The biological farming time could impact the changes of soil nutrients significantly (P0.05), and tightest rates of soil organic matter, total nitrogen, total phosphorus are generally in the third or second years of the biological farming. The activities of catalase, urease and sucrose are increased under the biological tillage compared with the no-tillage, and the highest increased rates are 27.78%, 951.11%, 16.11% and 420.00%. The enzyme activities are different (P 0.05) in farming times and soil layers. The correlation analysis shows that there are significantly positive correlations between the catalase activity and soil organic matter, total phosphorus, available N, available P,available K and water content. The regression analysis shows that the main factors of impacting soil enzyme activities are available nitrogen, potassium, available phosphorus, total phosphorus and water content which affect enzyme activities with single or comprehensive factors. The path analysis shows that the biological cultivation time directly influences the enzyme activities, for example, the catalase activity invertase activity urease activity protease activity. The direct path coefficients are 1.353, 1.070, 0.421 and 0.110 respectively, and the soil organic matter and the available nitrogen are main factors of impacting the enzyme activities with positive effects.