Effects Of Herbage Growth On Dynamic Changes Of Soil Aggregation And Nutrients

Herbage growth plays an important role in improving soil condition and preventing soil erosion. The pot experiments were conducted in greenhouse to study the impacts of three kinds of herbs (wheatgrass, tall fescue and alfalfa) on soil aggregate stability, soil organic matter, total N, NO3-N, NO4-N, available P, soil microbial biomass C and soil microbial biomass N, and discuss the effects of three kinds of herbs on improving the soil properties combined with the development of above-ground and below-ground at different stages, the main conclusions were as follows:1)Three kinds of herbs had different height, tiller (branches) quantity, above-ground biomass, below-ground biomass and root volume, and the above-ground biomass and below-ground biomass had significant difference between different herbs.2)The trend of mean weight diameter (MWD) of soil aggregate of tall fescue was similar with CK, and there is no change of MWD at four different growth stages. However, alfalfa and wheatgrass can significantly improve the soil aggregate stability. There were significant differences between 90d and 220d, 90d and 220d, 130d and 250d of soil MWD under wheatgrass treatment, and 250d and the other growth stages of alfalfa. Impacts of different herb types on soil aggregate stability in the same growth time varies. There were no significant differences among different treatments after 90d's growth, so was other stages between tall fescue and CK. There were significant differences between wheatgrass and CK, alfalfa and CK after 130d. Compared with growth time, ground biomass, underground biomass, growth time and herb types the most important factors in affecting soil aggregate stability3)Soil organic matter increased with herbage growth, and accelerated after 220d. Total N amount under Alfalfa treatment was higher than it under the other two treatments. Thus, total N, NO3-N, and NH4-N all turned decreasing trends along the whole living time of the three herbages.4)Compared with CK, soil microbial biomass C and N increased obviously with the herbage growth time, and they followed the order wheatgrass>tall fescue>alfalfa, and alfalfa >wheatgrass>tall fescue, respectively. There were significant differences among soil microbial biomass C contents of the three herbages, but no significant differences were found for soil microbial biomass N contents.5)Correlation analysis showed that plant growth time, ground biomass, and underground biomass are positively related to MWD. Moreover, there are positive relations among the growth time, ground biomass, under-ground biomass, tiller number and soil organic matter, soil microbial biomass C and N. The results showed that herb development improved soil structure and increased soil organic matter. And the varied effects of herbage growth on soil properties were found.