Effects Of Alfalfa Planting On Soil Physical, Chemical And Microbial Properties

In recent years, Wuwei City tried to promote the "agricultural facility" mode of production. Animal husbandry grew fast and cattle breeding developed rapidly. As a result, forage shortage became an important factor limiting the development of local animal husbandry. Alfalfa (Medicago sativa L.) is known as "the king of grass" with wide adaptability, strong stress resistance and high feeding as well as economic values. Alfalfa can improve soil moisture and nutrient storage, increase water use efficiency, improve soil fertility, help to fix sand and defend wind erosion. Therefore,:alfalfa with high ecological and economic values is a good forage in arid regions. In this paper, Longdong alfalfa and Suntory alfalfa planted with large area in Wuwei City were used as research objects. The physical, chemical and microbial community properties of soil planted with Longdong alfalfa in the first year (LD) and Suntory alfalfa in the first (S1), second (S2) and third year (S3) were studied. The aim of this research was to explore the influences of alfalfa types and growing stages on typical irrigated desert soil in Wuwei City. The main results are as follows:1. In the major growing seasons from May to November in 2012, the pH of the soil planted with LD, S1, S2 and S3 decreased first from May to June, and then gradually increased to a high level from June to November.2. The organic matter contents for LD, S1, S2 and S3 were 11.02g.kg-1,11.43 g.kg-1,11.26 g.kg-1 and 11.20 g.kg-1 respectively. The results indicate that planting alfalfa did not markedly affect soil organic matter content in the short term.3. The total nitrogen content of the soil in the reviving season was 0.394 g.kg-1. In the growing season LD, S1, S2 and S3 showed the total nitrogen content of 0.451 g.kg-1,0.468 g.kg-1,0.437g.kg-1 and 0.428 g.kg-1, respectively, and in post-harvest the content of 0.501 g.kg"1,0.498 g.kg-1,0.527 g.kg-1 and 0.501 g.kg-1, respectively. Application of fertilizers and crop roots might promote the mineralization of soil humus, and thereby increased soil nitrogen decomposition. However, no significant differences were found among the four treatments.4. The seasonal dynamics of soil phosphorus content for each treatment were similar, that is, the phosphorus content decreased during the forage growing season, while the level increased after harvest. The possible reason is that during the growing season, the absorption of phosphorus nutrient to the soil mineral surface might make the phosphorus unavailable. The soil phosphorus content in the non-growing season did not show significant differences among the treatments, whereas the differences between each growth period were significant. There was no definite trend for the potassium content of alfalfa soil during the whole season, and there was no significant differences between the treatments. The available phosphorus and potassium content showed significantly negative correlation with soil pH.5. The characteristic fatty acid ratio of fungi to bacteria for S3 changed obviously, compared with that for S1 and LD. Although the ratio was higher than that for LD2, the difference between the two treatments was not significant.6. The dynamics of bacteria, fungi and actinomycetes in LD, S1, S2 and S3 showed the same trend during the whole season, that is, the biomass peaked in July and August, and then decreased to a lower level until it reached the lowest value in November. The soil microorganism structures in LD, S1, S2 and S3 did not show significant differences (P>0.05). Microbial biomass decreased with the increase of soil depth, as the biomass in the topsoil (0-5cm) was significantly higher than that in the deeper soil (15cm and 30cm)7. The biomass of bacteria, fungi and actinomycetes for LD, S1, S2 and S3 showed significantly negative correlation with soil pH, which indicates that the bloom of microorganisms and the enhanced microbial activities could reduce soil pH.In summary, the experimental results suggest that the effects of alfalfa planting on the physical, chemical and microbial community properties of soil such as soil pH, organic matter content, total nitrogen content, nitrogen content and available phosphorus was well as potassium were complicated, since individual indicators showed different trends within the same season. Therefore, simply describe the raising or lowering of the fertility by planting alfalfa is not accurate, and a comprehensive methodology should be adopted for future alfalfa production in Wuwei City.