[Physical and chemical properties of soil bio-crust on rehabilitated grassland in hilly Loess Plateau of China].

Soil bio-crust (SBC) plays an important role in degraded ecosystem restoration. The field investigation and laboratory analysis of SBC on different year rehabilitated grasslands at the north slope of hilly Loess Plateau showed that after cropland shifted to rehabilitated grassland, rainfall- induced structural crust appeared firstly, and then, with the increasing year of rehabilitation, crust- forming microorganism gradually settled in, and SBC developed. The depth of SBC increased in inverse "S" shape with increasing year of rehabilitation. 10 years after rehabilitation, the increase of SBC depth slowed down, and soil bulk density decreased from 1.4 g x cm(-3) to 1.1 g x cm(-3). SBC formation improved soil cohesion significantly, and the latter was increased in inverse "S" shape with increasing year of rehabilitation. The organic matter and total nitrogen contents in SBC were obviously higher than those in cropland, and increased gradually with increasing year of rehabilitation but tended to be stable after 10 years of rehabilitation. The available N, P and K contents in SBC were also increased, but no significant difference of total phosphorus was found between SBC and cropland soil. The formation of SBC in test region could be classified into 3 stages, i. e., the first stage named the beginning of the formation, which was from 1 to 4 years of grassland rehabilitation, the second stage named the rapid development period, which was from 5 to 10 years of the rehabilitation, and the third stage named stable period after 10 years of rehabilitation.