Effects of different years of returning farmland on the soil nutrients and C, N and P reserves in grassland in Ningxia

Zhang Xiaoju;Mei Hang;Shen Yan;School of Agriculture, Ningxia University;Key Laboratory of Restoration and Rehabilitation of Degraded Ecosystem in Northwestern China, Ningxia University;

typical grassland area of Ningxia;;returning farmland;;soil nutrient;;measurement ratio;;reserves

With the implementation of the national strategy of returning farmland to forests and grassland, the changes of soil characteristics in the process of grassland vegetation restoration have been widely concerned. With the implementation of the national strategy of returning farmland to forests and grassland, the changes of soil characteristics in the process of grassland vegetation restoration have been widely concerned. The changes of soil nutrient, carbon and nitrogen reserves in different grassland years in Ningxia were analyzed to provide new references for environmental protection and restoration in this area. Using spatial gradient instead of time gradient method, 8 different grassland years(1995, 2000, 2005, 2007,2011, 2013, 2014, 2016) in the experimental area were selected for the purpose to study the nutrient characteristics of carbon, nitrogen and phosphorus, the ratio and reserves of C/N/P of soils, and discuss the effects on soil nutrient, C/N/P ratio and reserves caused by grassland years. The results showed that: ① Different years of returning farmland to grassland have significant effect on nutrient content of 0～40 cm soil(P<0.05). The overall changes of soil organic matter, total nitrogen, alkali nitrogen, available phosphorus and available potassium showed similar trends, both of which showed a trend of rising first and then decreasing, and the peak appeared after 9 years of returning farmland(2007). The total potassium content changed smoothly during the 0～21 years of returning farmland, and the difference of total potassium content in each year of returning farmland was not significant. The vertical change of soil nutrient in the grassland showed a trend of decreasing with the nutrient content of the soil layer, showing a certain surface layer(0～5 cm) enrichment. ②The soil C/N range in the test area ranged from 6.47 to 17.77, the N/P ranged from 0.95 to 1.99, and the C/P ranged from 11.49 to 18.88. The C/N and C/P were lower than the national average. It has high C and P availability. ③The soil organic carbon storage and total nitrogen storage in the 0 ～40 cm soil layer of the experimental area all showed a trend of increasing first and then steadily, reaching a peak in the 9 years of returning farmland(2007). The total phosphorus reserves of soil in 0～40 cm soil layer showed a steady trend.