Study On Change Of Alfalfa Biology, Water And Fertility Characteristics For Different Growing Years

Alfalfa (Medicago sativa L.) is not only an excellent perennial leguminous grass, but also that can improve soil. It has a broad adaptability in arid and semi-arid areas, China. In the research, material is alfalfa of different growth years in longdong in Gansu province, Loess Plateau of China, where is a very typical area of planting alfalfa. To provide scientific basis for management of alfalfa field in arid and semi-arid areas, changes of alfalfa fresh grass yield, biological characteristics, soil water content, soil nutrient, soil urease activity, soil catalase activity are studied and the forming reasons of grassland degradation are analyzed. The results are as follows:1. With the plant growth year of alfalfa, the yield of different growth year is firstly increased and then decreased. The highest yield is occurred in 6 and 7 years. From the 8 growth years on, the alfalfa yield is declining and the first cutting yield is higher than the second cutting.2. Biological characteristics of different alfalfa growth years are showed that the changes between stem diameter, plant height, shoot number, branch number and fresh yield are similar. The dry weight of root segmentation is decreased slowly with the root length of alfalfa and is firstly increased then decreased with the plant growth year of alfalfa.3. Soil water content of the first cutting and the second cutting in two continuous years is studied Results showed that soil water content of 60~80cm layer is highest in the first cutting, and dry layer is gradually deepened with the root length of alfalfa; soil water content of surface layer is the highest in the second cutting, which is related to seasonal rainful in Loess Plateau of China. Soil bulk density in 6 years is higher than other years, especially in 20～40cm layer. There are no significant differences among alfalfa growth years.4. Changes of soil total nutrient in different growth years are showed that SOM and STN contents are reached highest at surface layer, and then are declining with the depth of soil layer, STP content is stable with the depth of soil layer and there are no significant differences among alfalfa growth years. 5. Changes of soil available nutrient of 0~1000 layer are studied. It is showed that soil available N content of surface layer is highest, soil available N content is declining gradually with the depth of soil layer, soil available N content of 180~200 layer is lowest and change of layers under 200cm is ont obvious. Changes of soil available P content are opposite to soil available N. Soil available P content is lowest in surface layer and is increased gradually with the depth of soil layer; in the range of 0~400cm soil available P content is declining with the depth of soil layer and change of layers under 400cm is not obvious.6. Soil urease activity is highest of surface layer, and is declining with the depth of soil layer. Soil urease activity of 40～60cm layer is lowest and under the 40~60cm layer changes of soil urease activity are not obvious. There are no significant differences among different alfalfa growth years; with the depth of soil layer, changes of soil catalase are not obvious. Soil catalase activity trend of different growth years is 5a>4a>7a>9a>11a>27a>19a and soil catalase activity of 19a is not significantly diffenent from 27a.