The Response Of Soil Environment To Grow Of Caragana Korshinskii Plantation In Loess Hilly Region

This study took Caragana Korshinskii plantation, a typical artificial shrub stand in loess hilly region as object, investigated the changes of soil environmental factors during the growth of Caragana Korshinskii with different stand ages, explored the response mechanism of soil environmental factors to recovery of artificial vegetation, assessed the soil fertility and quality under Caragana Korshinskii plantation, revealed the intrinsic law between the growth of typical artificial vegetation and the changes of soil environment. This study was conducted in order to provide scientific basis for constructing artificial vegetation on Loess Plateau, and was important in theoretical and practical sense both for ecological environment construction and implementation of the Grain for Green Project. The results showed that:(1) As a Caragana Korshinskii plantation aged (10a-50a), its above ground and root biomass both increased. The above ground and root biomass of 50 years old plantation were 37.62% and 215.67% higher than that 10 years old, respectively. As regards slope aspects, the above ground and root biomass on shady slope were 42.28% and 24.66% higher than that on sunny slope, respectively. On soil profile, the top layer (0-10 cm) contained the highest biomass, then the layer of 10-20 cm depth, and the biomass in those two layers accounted for more than 50 % of the total biomass in 0-60 cm depth. The lower layers (20-60 cm) didn't present obvious differences in biomass, which was less than top layer.(2) As a Caragana Korshinskii plantation aged (10a-50a), soil water content decreased gradually, meanwhile, soil bulk density, total porosity, and capillary porosity were generally improved. Compared to plantation 10 years old, soil bulk density, total porosity, and capillary porosity of 50 years old plantation changed by -10.17%, 10.35%, and 13.00%, respectively. All of the physical properties of soil under Caragana Korshinskii plantation were better on shady slope than that on sunny slope. Soil water content, bulk density, total porosity, and capillary porosity on shady slope varied by 17.70%, -0.45%, 3.94%, and 7.45% compared to those on sunny slope, respectively. Caragana Korshinskii plantation improved soil bulk density, total porosity, and capillary porosity at top layer (0-10 cm) most significantly. The improvement effect was less obvious as soil depth increased.(3) As a Caragana Korshinskii plantation aged (10a-50a), the indices of chemical properties of soil all increased to certain extents. The organic matter, total N, total P, available P, and available K of 50 years old plantation increased by 114.25%, 84.50%, 9.61%, 122.31%, and 42.68% than 10 years old plantation, respectively. All of the chemical properties of soil under Caragana Korshinskii plantation were better on shady slope than that on sunny slope. The organic matter, total N, total P, available P, and available K on shady slope were 29.20%, 24.34%, 28.84%, 36.90%, and 31.82% higher those on sunny slope, respectively. The improvement effect of Caragana Korshinskii on soil chemical properties declined with layer depth increased, and this trend was not obvious for total P. The concentration of organic matter, total N, available P, and available K in soil all appeared a"top concentration"phenomenon, and was at relatively low levels in lower soil layer.(4) The soil organic matter was positively correlated with all the measured chemical property indices highly except total P. Total N, available P, and available K were positively correlated with each other significantly. The above ground biomass of plantation was positively correlated with root biomass significantly. The root biomass was negatively correlated with soil bulk density significantly, positively correlated with soil organic matter, total N, available P, available K, total porosity, and capillary porosity highly, which reflected the close relationship between Caragana Korshinskii roots and physical and chemical soil properties, a mutual affection and improvement relationship. The soil bulk density was negatively correlated with total porosity, capillary porosity, root biomass, organic matter, total N, and available P significantly.(5) The fertility of soil under Caragana Korshinskii plantation gradually increased with stand age. When the plantation was 10-26 years old, the soil fertility was in a rapid increasing period; when 26-30 years old, a fluctuation occurred, oil fertility decreased a little; when 30-50 years old, the soil fertility increased steadily, and reached the highest value. The soil fertility of 10 and 17 years old plantation was the 4th rank (the worst rank), the soil fertility of 30 years old plantation was the 3rd rank (the bad rank), the soil fertility of 26, 34, and 40 years old plantations was the 2nd rank (the middle level), and the soil fertility of 50 years old plantation was the 1st rank (the high level).