Study on soil physical and chemical properties and carbon and nitrogen sequestration of grassland under different utilization modes

Abstract

This research investigated the effects of natural grassland and artificial grassland degradation on soil physical and chemical properties, in particular the change in carbon and nitrogen contents and carbon sequestration. Representative areas of natural grassland, grazed artificial grassland and mown artificial grassland in Ar Horqin Banner, Inner Mongolia, were selected for study. Parameters measured in the study area were soil moisture content, soil bulk density, soil microbial content and soil nutrient levels. Growth status of the study sites was also evaluated using the NDVI value and in general the ranking for growth status under the different utilization modes was: mown artificial grassland>grazed artificial grassland>natural grassland. Soil water content in the 0-20 cm depth ranked: grazed artificial grassland>mown artificial grassland>natural grassland, and the differences were significant (P<0.05). The total carbon and total nitrogen contents in the grazed artificial grassland were the highest. The total carbon contents in the grazed artificial grassland and natural grassland for the 10-30 cm soil depth were significantly higher than that of the mown artificial grassland (P<0.05). The total soil nitrogen content of the grazed artificial grassland for the 0-10 cm soil depth was (0.88±0.11) g•kg-1, which was significantly higher than those of the natural grassland and the mown artificial grassland (P<0.05). The soil microorganism carbon and nitrogen content in the three grassland types ranked: grazed artificial grassland>mown artificial grassland>natural grassland. The soil microorganism nitrogen content of the grazed artificial grassland for the 0-10 cm depth was (28.45±8.30) mg•kg-1, which was significantly higher than values in the natural grassland and mown artificial grassland (P<0.05). Soil carbon and nitrogen storage for the three categories of grassland ranked: natural grassland>grazed artificial grassland>mown artificial grassland, and soil carbon and nitrogen storage of natural grassland and grazed artificial grassland for the 10-30 cm depth were significantly higher than that of mown artificial grassland (P<0.05). The performance characteristic of grazed artificial grassland was soil carbon and nitrogen accumulation, while that of mown artificial grassland was carbon and nitrogen loss. In addition, with increase in soil depth, the carbon and nitrogen storage of natural grassland and mown artificial grassland show a decreasing trend. Thus it can be seen that the establishment of artificial grassland and human intervention such as seeding and irrigation will effectively improve soil quality and grassland growth status, but to a certain extent there may be a negative effect on soil carbon and nitrogen sequestration potential.