The Influence Of Planting Alfalfa On The Physico-Chemical Characteristics Of Soil

Under the experimental field's condition of non-fertilization and non-irrigation, dynamic changes of raw and mellow soil's physico-chemical characteristics in different planting years and different soil layers were studied. The objective of this study was to evaluate effects of alfalfa on improving soil, enriching fertility and alfalfa-crop rotations. The main conclusions were as follows.1. After planting alfalfa, the contents of soil nitrogon and soil organic matter were improved as a whole, but in seedling stage, alfalfa nodule was not strong and enough, soil nitrogon was consumed during this period, from the third planting year on, nitrogen fixation of soil was significant. After planting alfalfa, contents of each soil layer's organic matter, total N and available N were decreased to the lowest level in the second planting year, improvements of soil total N and organic matter content were not obvious after only planting alfalfa one year. Contents of soil organic matter, total N and available N were reached peak volume at the fourth planting year, which were very significantly increased comparing with planting alfalfa(p<0.01). On profile, the increasing ranges of each layer'soil organic matter, total N and available N in mellow soil were higher than raw soil, and the highest content of soil organic matter, total N and available N all were occurred in the layer of 0~20cm, with the depth of soil layer, all the contents were decreased (except soil organic matter of raw soil) and presented regular change.2. After planting alfalfa three years, the influence on the content of soil total P was not significant, soil total K content was lowered. In the fourth planting year, the difference of soil total P was not significant comparing with planting alfalfa, the content of each layer's total K was decreased and reached lowest level, soil total K content was significantly lowered comparing with planting alfalfa(p<0.01). Comparing with planting alfalfa, soil total K content in 0~20, 20~40, 40~60cm in raw soil was decreased 1.23, 1.12, 1.06g/kg, soil total K content in 0~20, 20~40, 40~60cm in mellow soil was decreased 1.31, 1.12, 1.06g/kg. On profile, the decreasing range of each layer's soil total K in mellow soil was higher than the raw soil.3. Contents of soil available P and available K were decreased after planting alfalfa. Soil available P content in each layer was decreased and reached lowest level at the fourth planting year, which was significantly lowered comparing with planting alfalfa(p<0.01), but comparing with planting alfalfa, soil available P content was not significantly different. Soil available K content was reached lowest level at the fourth planting year, comparing with planting alfalfa, soil available K content in 0~20, 20~40, 40~60cm in raw soil was decreased 127.71, 114.57, 126.48mg/kg, soil available K content in 0~20, 20~40, 40~60cm in mellow soil was decreased 140.07, 116.80, 113.03mg/kg, which was showed that after planting alfalfa, the influence on soil available K content was obvious, long-term planting alfalfa was caused the scarcity of soil K.4. Soil pH value was increased and soil bulk density was decreased after planting alfalfa three years. After planting alfalfa, soil pH value in each layer was increased slowly, and was reached peak volume at the fourth planting year, which was significantly increased comparing with planting alfalfa(p<0.01). Comparing with planting alfalfa, the second planting year and third planting year were not significant different. Soil pH value in 0~20, 20~40, 40~60cm in raw soil was increased 0.24, 0.22, 0.11, soil pH value in 0~20, 20~40, 40~60cm in mellow soil was increased 0.25, 0.22, 0.22. After planting alfalfa, soil bulk density in each layer was decreased slowly and reached lowest level at the fourth planting year, which was significantly increased comparing with planting alfalfa(p<0.01). Comparing with planting alfalfa, the second planting year and third planting year were not significant different. Soil bulk density in 0~20, 20~40, 40~60cm in raw soil was decreased 0.21, 0.19, 0.18g/cm3, soil bulk density in 0~20, 20~40, 40~60cm in mellow soil was decreased 0.12, 0.11, 0.13g/cm3, which was showed that soil pH value, soil bulk density was closely related with the number of growing years of alfalfa.