Physical and chemical properties of soil in alfalfa field for different cultivated years

The present study evaluated soil physical and chemical properties in alfalfa field for different cultivated years in semiarid region. The results showed that with the cultivated period increasing, the soil bulk density changed irregularly with relative high values. Soil organic matter increased with the alfalfa’s growing years, while decreased significantly withthe increased depth of soil (P<0.01). Soil organic matter in five years alfalfa field had the highest increase whereas it was the lowest in the eight years alfalfa field. There was characteristic of soil organic matter surface accumulation for each experiment site and there were accumulation only in range of cultivated period. Soil total nitrogen content firstly increased and then decreased with the cultivated period increasing, but decreased with the soil depth increased. Soil total nitrogen content reached the peak in four years alfalfa field and reached the minimum in eight years alfalfa field. And soil total nitrogen content mainly accumulated in 0-40 cm of soil layer which suggested that soil total nitrogen significantly accumulated in the surface soils. Soil nitrate nitrogen content firstly increased and then decreased with the cultivated period increasing, but decreased with the soil depth increased. Soil nitrate nitrogen content accumulated in the surface soil of 0-5 cm. There was significant correlation between soil nitrate nitrogen content and the growing time of alfalf (P<0.05). Soil ammonium nitrogen did not changed a lot in the soil profile which had no significant correlation with the growing time of alfalfa. The management measures to improve the best cultivation and utilization year in cultivated alfalfa field need be further studied.