Effects of different small grain crops and fertilizations on soil nutrients and soil enzyme activities

Soil chemical characteristics and enzyme activity are closely related to crop types and fertilizations, which are important indexes to soil fertility.In order to determine the effects of different small grain crops and fertilizations on soil pH, nutrient contents and soil enzyme activities in black soil area, leguminous crops (mung bean and red bean) and gramineous crop (sorghum) after four-year continuous cropping with 3 fertilizations including no fertilizer, chemical fertilizer and organic fertilizer were examined.The results showed that fertilization reduced the soil pH of 3 small grains, but no differences were observed among treatments.The reduction of soil pH in gramineous crop was higher than that of legumes.In mung bean planting soil, the contents of total nitrogen (TN), available nitrogen (AN), total phosphorus (TP) and available phosphorus (AP) significantly increased 18.4%, 23.1%, 21.7% and 67.2% compared with no fertilizer application, while organic fertilizer application significantly increased soil TN and available potassium (AK) contents than that of chemical fertilizer application treatment.In red bean planting soil, chemical fertilizer significantly increased the content of soil AP and AK, and organic fertilizer application significantly increased the content of soil AK compared with no fertilization.In sorghum planting soil, chemical fertilizer application significantly increased the content of soil AN but reduced the content of soil AK, while organic fertilizer significantly increased the content of soil AN, AP and AK.In terms of soil enzyme activities, except the lower soil phosphatase activity in red bean than that of sorghum under chemical fertilizer treatment, the activities of sucrase, urease and phosphatase in leguminous crops soils were higher than that in sorghum soil under the same fertilization.The catalase activity of sorghum soil was higher than that of leguminous crops.Therefore, fertilization and types of small grain crops are both important factors affecting soil chemical properties and soil enzyme activities.