Effects Of Nitrogen Forms On Growth And Physiological Characteristics Of Alfalfa At Different Growth Stages

Alfalfa (Medicago sativa L.) as a high quality legume, it can use the symbiotic nitrogenfixing bacteria in root nodules of direct absorption molecular nitrogen in the air, but thisprocess is often affected by the ecological environment, especially in nitrogenenvironment.Effects of nitrogen application, nitrogen forms and application time on thegrowth and physiological characteristics of alfalfa, not only has a certain effect on yieldincrease of alfalfa, but also has a great significance on sustainable development of animalhusbandry in China.In this study, the complete nutrient solution with sand culture potexperiment, used Gannong No.3alfalfa as material,3kinds of exogenous nitrogen forms:NO3--N, NH4+-N and mixed nitrogen (NO3--N and NH4+-N as1∶1mixing ratio) and3nitrogen levels:0,105,210mg. L-1,according to the previous experimental results, tocomparative study of3nitrogen levels on the12531rhizobium inoculation in differentgrowing stages and the affect on growth and physiological characteristics of alfalfa.Conclusions are as follows:1, Whether NO3--N, NH4+-N or mixed nitrogen treatment, plant height and biomass ofalfalfa were significantly higher than that of nitrogen free treatment, stem leaf ratio werelower than no nitrogen treatment, therefore, a moderate amount of nitrogen in alfalfaproduction can effectively improve the production performance. And210mg/L was the bestnitrogen levels of alfalfa growth and mixed nitrogen was the best N forms of alfalfa growth.2, The effect of3kinds of different N forms processing on underground biomass, rootlength, root surface area, root volume, root average diameter, root number and root activity ofalfalfa were as follows: mixed nitrogen culture conditions was the best, NH4+-N training wasthe next one,NO3--N training was the lowest. Thus, alfalfa root growth performance bestunder mixed forms of nitrogen. Under three nitrogen levels, alfalfa underground biomass,root length, root surface area, root volume, root average diameter, root number and rootactivity reached maximum in nitrogen concentration of210mg/L showed that210mg/L fornitrogen level was the best conducive to the growth of root system.3, Alfalfa nodule number, nodule weight, nitrogenase activity and total nitrogen contentwere performance as follows: the best one was mixed nitrogen culture conditions, NH4+-N training was the next, NO3--N training was the lowest; NO3--N content and nitrate reductaseactivity performance best in NO3--N culture conditions, the mixed nitrogen to cultivate wasthe nextone, NH4+-N training was the lowest, NH4+-N content was the best under the NH4+-Ntraining, mixed nitrogen to cultivate was next one, under NO3--N training was the lowest.Thus, mixed nitrogen forms was suitable N forms for alfalfa nodular nitrogen fixation andnitrogen utilization. With the increase of nitrogen levels, alfalfa nodule number, noduleweight, nitrogenase activity, total nitrogen content, the content of NO3--N, the content ofNH4+-N and nitrate reductase all showed increasing trend, the highest nitrogen concentrationwas210mg/L.4, In the whole growth period, growth characteristics, root system characteristics andnodular nitrogen indexes of alfalfa’s performance trend changed as the growth periodadvanced had the first increases and then, alfalfa growth best with N forms was the mixedstate and nitrogen level was210mg/L. The differences between the groups of seedling stage,budding stage and flowering stage were obvious, the differences between the groups ofpodding stage and drum stage was not obvious, the seedling stage and nitrogen fertilizercould promote the growth of alfalfa. In the production practice, therefore, should be usednitrogen fertilizer early in alfalfa growth, nitrogen use efficiency, reduce unnecessary waste.