| Alfalfa (Medicago sativa ) is a qualified perennial legume with its high protein content, multiplex vitamin and minerals. Alfalfa is also a deeply rooted perennial legume, which can absorb water and nutrients from deep soil, decrease surface runoff and conserve water and soil. Alfalfa is widely grown all over the world, but mainly in neutral and lightly acid soils in north of China. Few varieties are distributed in acid soils.Alfalfa varieties, introduced from abroad or cultivated in north of China, are adapted to soils with pH 6.5 to 7.5. In south of China, especially in the south of Yangtze river, heavy rain enhances soil acidity, decreases the rhizobial affinity for host plant, limits the survival of rhizobia, and inhibits biological fixation of legumes. Acid soils also limit plant growth due to lack of available nutrients, ion imbalance, and high concentration of activated aluminum and H+.In order to enlarge planting area of alfalfa and develop alfalfa industry in south of China, it is necessary to improve environmental conditions for bio-fixation, to increase nutrients uptake of alfalfa from acid soil and to enhance the adaptability of alfalfa to acid soils. However, there still has no report on growing alfalfa in acid purple soil. So, several alfalfa varieties were selected to carry out experiments in classic and representative acid purple soil in Chongqing. The followings are the main conclusions:In trial one, the root and shoot growth index, nutritional characteristics of 6 alfalfa varieties and the nodulation capability of 2 R.meliloti were studied with pot experiment in acid purple soil(pH5.45). The 6 alfalfa varieties were Zhongmu 1, Gannong 1, Gannong 3, Sanditti, Eureka and Defi. The 2 R.meliloti were R.meliloti 1.163 and 1.159. The results showed that different varieties of alfalfa had different tolerance to acid soil. Alfalfa Sandtti was the best among the 6 alfalfa varietiesjudging from shoot yields. Clustering analysis, based on shoot, root growth index and nodule capability of different alfalfa varieties, also showed that Sandtti was the best.The correlation analysis indicated that height of alfalfa was significantly and positively correlated with stem / leaf ratio, but not with shoot dry weight. It meant that internodes elongation relatively decreased the leaf amount. While branching number of alfalfa was significantly and positively correlated with shoot dry weight and stem/leaf ratio. The contribution of branching number on yield per plant was higher than that of height. Root collar diameter was significantly and positively correlated with root weight, root/ top ratio, nodule weight and nodule number per pot. Root collar diameter is easy to be measured and could be an important index in judging root development of alfalfa in acid soils.There was significant difference on nodule number and nodule weight per pot between 2 R.meliloti. Compared with R.meliloti 1.159, R.meliloti 1.163 had better nodulation capability, distributed uniformly on root, and was more adaptable to acid purple soil. Different R.meliloti also influenced the nutrients uptake of alfalfa plants. The uptake of nitrogen, phosphorus, potassium, calcium and magnesium in shoot were higher in plant inoculated with R.meliloti 1.163 than that with Kmeliloti 1.159, while the uptake of aluminum was the same. Different varieties of alfalfa also had significant difference on nodulation capability. Inoculated with R.meliloti 1.159 or 1.163, nodule weight of Sandtti was the highest among the 6 varieties. Nodulation capability directly influenced the yields of alfalfa. Shoot yield of alfalfa plants was significantly positively correlated with nodule weight and nodule number.Shoot weight, nodule weight and number, nitrogen content in alfalfa were significantly and negatively correlated with aluminum content in alfalfa root. Over absorption of aluminum inhibited nodule development and nutrients uptake, and thus the adaptability of alfalfa to acid soil. The nutrients accumulation of different alfalfa varieties was also different. Among the 6 varieties, total accumulation of phosphorus, potassium, calcium, magnesium and aluminum of Sandtti was the highest. It meant that nutrients efficiency of Sandtti was the best.In trial two, the effects of liming on growth, nutrients uptake and nodulation capability of alfalfas were studied in acid purple soil. The results showed that different varieties of alfalfa had different responses on liming. Among the 6 varieties, the shoot weight of Sandtti and Defi decreased, while the others increased. As to Sandtti, branching number, shoot weight and main root length were decreased after liming, while growth height, root weight and the ratio of root and shoot increased. Liming limited the accumulation of shoot biomass of Sandtti. Whether liming the acid soil or not before planting alfalfas depends on specific alfalfa variety.After liming, the contents of nitrogen and phosphorus in shoot and root of most varieties increased, the content of potassium decreased. The changes of the contents of calcium, aluminum and magnesium were different among varieties. As to Sandtti, content of calcium, magnesium and aluminum in shoot and root decreased, except for magnesium content in root. Liming significantly decreased nodule weight and nodule number of alfalfas, inhibited nodule development. The mean nodule weight was decreased after liming.In trial three, seed emergency, early growth and nodulation capability of alfalfa Sandtti in acid purple soil(pH5.45) were studied. The results showed that seed emergency was affected by soil acidity. Seed emergency of alfalfa was about 70% in acid soil. 30% more seed quantity was needed to maintain certain productivity of alfalfa. Soil pH value increased about 1 after liming, but no significant increment of seed emergency was found. More than soil acidity affected seed emergency of alfalfa in acid purple soil.Alfalfa grew normally in acid purple soil during the early time, and root grew faster than shoot. Better development of root in acid soil was an important factor for later growth of alfalfa plant. It also meant that alfalfa Sandtti could adapt to the acid purple soil. Alfalfa root nodule appeared after sowing 25 days. And nodule number increased with the growing time. It indicated that Rhizobium meliloti could infect alfalfa root normally in acid purple soil. After liming, first nodulation time of alfalfa was delayed and nodule number was decreased. No liming was needed in growing alfalfa in this type of soil.In trial four, the infection of 4 VA mycorrhizal fungi on alfalfa and their effect on growth and nodulation ability of alfalfa were analyzed in sterilized acid purple soil. The results showed that G.intraradices and G.spp promoted plant growth, G.caledoium and A.leavis caused leaf abscission, inhibited plant growth. The distribution of biomass between shoot and root was also influenced by VA mycorrhizal fungi. G. intraradices relatively promoted shoot growth, while G.spp, G. caledoium and A.leavis relatively promoted root growth.G.intraradices, G. caledoium and A. leavis significantly decreased nodule weight per pot. The infection of nodule bacteria and nodule development of alfalfa were inhibited by these fungi. While G.spp promoted nodule development, and the nodule weight of alfalfa increased 4.28%.The contents of nitrogen, phosphorus, calcium and magnesium in shoot were increased after inoculated with G. intraradices, G.spp, while the content of potassium and aluminum in shoot decreased. Total accumulation of nitrogen, phosphorus, calcium, magnesium and aluminum in plants inoculated with G.spp was the highest. It was feasible to promote alfalfa growth in acid soils by inoculating alfalfa with VA mycorrhizal fungi. And G.spp, among the 4 VA mycorrhizal fungi, was the first choice to be used in fields.
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