Effects of degraded sandy grassland afforestation on soil quality in semi-arid area of Northern China
半干旱区沙质退化草地造林对土壤质量的影响

By the methods of field survey and incubation test,this paper studied the effects of degraded sandy grassland afforestation with Mongolian pine on the soil physical,chemical and biological properties in 0-10 cm layer on Keerqin sandy land.The results showed that after 32 years afforestation,soil organic C,total N and total P decreased by 21%,42% and 45%,respectively.In May and November,soil NH4 -N content was significantly higher under Mongolian pine plantation than under grassland(P=0.001;P=0.019),but in May,August and November,soil NO3--N content was in adverse(P<0.001;P=0.048;P=0.031).In May,August and November,soil C mineralization rate was higher under Mongolian pine plantation than under grassland,but the difference in N mineralization rate was not significant(P>0.05).In May and August,soil microbial biomass C under Mongolian pine plantation and grassland had little difference,but in November,it was significantly higher under Mongolian pine plantation than under grassland.Soil nutrients-and moisture contents were the important factors affecting soil microbial biomass C.Soil urease and invertase activities decreased but catalase activity increased under Mongolian pine plantation,compared with those under grassland.It was suggested that 32 years afforestation of degraded sandy grassland with Mongolian pine on Keerqin sandy land led to a definite degradation of soil quality.Owing to the changes of vegetation,the test indicators of soil quality had different seasonal dynamic characteristics under Mongolian pine plantation and grassland.As a means of degraded ecosystem restoration in semi-arid area of Northern China,afforestation had its definite limitations.