Assessment of soil enzyme activities of saline–sodic soil under drip irrigation in the Songnen plain

A field experiment was carried out to research the changes and spatial distributions of soil enzyme activities in saline–sodic soil for a different number of cultivated years under drip irrigation. The distributions of alkaline phosphatase, urease, and sucrase activities within 40 cm in both horizontal and vertical directions of the emitter in saline–sodic soils planted with Leymus chinensis for 1st, 2nd, and 3rd year were studied. A mathematical method was used to determine the relationships between soil enzyme activities and soil environmental factors contain the electrical conductivity of saturated-soil extract, pH value, available nutrient, and organic carbon. Alkaline phosphatase, urease, and sucrase activities all increased with cultivated years in saline–sodic soil under drip irrigation: from 4.5, 1.39 and 19.39 to 20.25, 3.17, and 61.33 μg g−1 h−1, respectively, after planting L. chinensis for 3 year. Alkaline phosphatase, urease, and sucrase activities all decreased with increased horizontal and vertical distance from the emitter. After 3 year of drip irrigation, the correlations between soil enzyme activities and soil environment factors had stronger correlations than in the unreclaimed land. After 4–6 years, the soil enzyme activities should attain the level of the natural L. chinensis grassland.