Effects of the conversion time of cropland into forestry on soil physical properties in loess area of western Shanxi Province of northern China

ObjectiveIn order to discuss the “Grain for Green Project” on improving the soil physical property, we did an analysis about the change of soil physical property in different ages.

MethodThe paper selects three kinds of land use (grass, pure plantation, mixed plantation) in the loess area of western Shanxi Province, contrasting with farmland, to discuss the effects of various ages in the Grain for Green Project on soil physical properties such as soil bulk density, soil total porosity and capillary porosity.

ResultThe soil bulk density increased significantly with soil depth. The mean soil bulk density of 0−60 cm soil layer was farmland (1.38 g/cm³) > grassland (1.27 g/cm³) > pure plantation (1.20 g/cm³）> mixed plantation (1.18 g/cm³). There were significant differences in the soil bulk density of woodland and grass, farmland (P < 0.05). Besides, the soil bulk density decreased as the increasing year since abandoned. The value of it had been stable in 1.16 g/cm³ after 23 years old. The best improvement effect was the topsoil, but faded away with the increasing soil depth. The total porosity was inversely proportional to the age and tended to vary gently with increasing age of stand. The value of total porosity of topsoil was the biggest, which was 50.8%−57.6%, and the periods of greatest change was 5−10 years old. The value of it had been stable in 55.61% after 25 years old. The mean in the layers of 0−60 cm was mixed plantation (53.67%) > pure plantation (52.87%) > farmland (47.82%) > grassland (45.97%). There were significant differences between the grassland, farmland and woodland in the total porosity (P < 0.05), and the pure plantation was significantly different from the mixed plantation. With the growth of forest age, the capillary porosity also increased. The value of the mixed plantation and the pure plantation was 52.21% and 50.37%, which was significantly different from the farmland (45.62%).

ConclusionThe project of the Grain for Green can obviously improve soil physical properties, and the effect of mixed plantation on soil improvement is better than pure plantation.