Effects of Amorpha fruticosa planting on soil nutrient characteristics at rhizosphere andnon-rhizosphere in Tibetan Plateau

The soil nutrients of Amorpha fruticosa cultivated in Lhasa, Tibet were measured in continuous three years from 2010-2012 when the plants were 1-year-age, 2-year-age and 3-year-age, respectively. The test indices included total nitrogen, total phosphorus, soil organic carbon, nitrate nitrogen, ammonium nitrogen, pH and available phosphorus from the rhizosphere and bulk soil. The results indicated that all parameters of the 1-year-age and 2-year-age A.fruticosa showed the positive rhizosphere impacts. However, all parameters except with pH and available phosphorus of the 3-year-age A. fruticosa didn’t show positive rhizosphere impacts. There was no significant variation of soil total nitrogen and phosphorus in rhizosphere and bulk. With the extension of cultivation years, the nitrate nitrogen and ammonium nitrogen of both rhizosphere and bulk soil increased, however, the pH values and available phosphorus decreased. The organic carbon of bulk soil increase with the extension of cultivation years, however, the organic carbon of rhizosphere soil increase in the second year and decrease in the third year. The total phosphorus of rhizosphere soil had a extremely significant positive correlation with total nitrogen and available phosphorus (P0.01). The pH values of rhizosphere soil had a significant negative correlation with the ammonium nitrogen (P0.05) and had a significant positive correlation with available phosphorus (P0.05). The ammonium nitrogen of rhizosphere and bulk soil had a significant positive correlation with the nitrate nitrogen (P0.05). The ammonium nitrogen of bulk soil had a significant negative correlation with the pH values and available phosphorus (P0.05). The pH values of bulk soil had a negative correlation with ammonium nitrogen (P0.05) and a positive correlation with available phosphorus (P0.05).