Abstract:

A field test was conducted by control and urease inhibitor, water retaining agent, intercropping arrow pea and rapeseed green manure (marked as by CK, T₁, T₂, T₃ and T₄) in 8 years Lycium chinense orchards in Yellow River irrigation area of Ningxia. The aim was to study the nitrogen transformation and leaching characteristics in the soil, providing theoretical and technical references for efficient utilization of nutrients in farmland and water quality protection in the Yellow River Basin. The results showed that: (1) soil pH reduced significantly under T₁ treatment, surface soil water content was increased under T₂ treatment in the second year. After planting two kinds of green manure, the bulk density of the surface soil decreased significantly and the soil moisture content increased significantly. (2) In the first test year, the microbial biomass carbon (MBC) of T₃ and T₄ treatments increased by 33.2% and 48.4% respectively compared to CK. However, in the next year, the total soil organic carbon (SOC) increased by 3.65% and 4.59% respectively, and the MBC increased by 50.3% and 59.2% respectively. (3) The soil MBN of T₃ and T₄ treatment increased by 45.1% and 42.6% respectively compared to CK in the first year, and they increased by 95.9% and 80.7% in the second year, respectively, and T₁ decreased by 28.5% compared to CK. After two years of application of T₁, the soil NH₄⁺-N increased by 71.7% and 75.4%. NO₃^--N of T₃ and T₄ increased by 46.7% and 41.8% respectively in the first year compared to CK, and in the next year they increased by 22.5% and 13.4%. (4) The changes of NH₄⁺-N content in soil profiles over two years mainly occurred in 0-40 cm, while NO₃^--N content mainly occurred in 0-40 cm in the first year and 0-60 cm in the second year. The upper soil NH₄⁺-N and NO₃^--N (above 60 cm) by T₁, T₃, and T₄ treatments were significantly higher than those in other treatments. In a conclusion, application of urease inhibitors leaded to a decrease in soil pH and MBN, resulting in the formation of more NH₄⁺-N; planting two types of green manure could loosen the soil, increase MBC and MBN, and promote organic nitrogen mineralization. Moreover, the two types of green manure had a significant inhibitory effect on NO₃^--N leaching into deeper layers in Lycium chinense orchards in Ningxia. Therefore, it was recommended that intercropping arrow pea and rapeseed manure in Lycium chinense orchards had significant effects on efficient nitrogen fertilizer utilization and prevention of water pollution.

Key words: Lycium chinense, soil organic carbon, nitrogen, transformation, leaching, farmland in the Yellow River irrigation area