Abstract:

This research investigated soil physical and chemical properties and soil microorganism presence for five sites forming a time series （1， 2， 8， 13， 20 years since cessation of farming） for recovery of degraded grassland in Minqin County， Gansu Province. Soil physical and chemical properties measured included pH， moisture content， sand content， total nitrogen， available potassium and available phosphorus. Soil microbial determinations included comparative abundance of the three main taxonomic groups （bacteria， actinomycetes and fungi）， and soil microbial biomass （carbon， nitrogen， phosphorus） and their correlation. It was found that bacteria were the most abundant soil microorganism， while actinomycetes and fungi were less abundant. With increase in years of recovery， soil sand content， total nitrogen， available potassium， soil microbial biomass carbon， soil microbial biomass nitrogen， soil microbial biomass phosphorus and other indicators showed an initial rise and then a decline trend. For soil moisture content， available phosphorus， bacterial population count， and actinomycete abundance showed a decreasing trend in different degrees. Difference in recovery time did not significantly affect the soil pH or the soil fungal content. There is a certain correlation between soil physical and chemical properties and soil microorganism properties. The results of multivariate evaluation of soil fertility data show that eight years was the time by which key changes were achieved in the recovery of degraded grassland in abandoned farmland areas in Minqin.

Key words: abandoned land, soil physical and chemical properties, soil microorganism abundance, dynamic variation