Studies On Nitrogen For Seedling Growth In Alfalfa

Alfalfa(Medicago sativa L.)for seasonal growing in winter-followed farmland has played an important role in livestock development in southern China.In this seasonal cultivation system of alfalfa,it is usually planted in autumn,and cut twice or three times in the next spring year.Alfalfa growth faced challenges as a fast-growing seasonal cultivar when planted in winter fallow fields in the southern China,due to local afro-ecological conditions and growth period,which resulted in decreasing root growth and also lead to a decline in nitrogen fixation ability of rhizobium.Therefore,nitrogen fertilizer is needed in obtaining high yield of seasonal cultivation of alfalfa.However,there were little information about the technology of fertilizer in the seasonal cultivation system of farmland ecological conditions of south China.Different fertilizer levels(Hoagland nutrient solution concentration)and nitrogen treatments are two important parts in alfalfa fertilization technology,The experiment was carried out in pot trials with quartz sand and nutrient solution to study the effect of different Hoagland nutrient solution concentration and nitrogen treatments on growth of alfalfa seedling,in order to provide reference for seasonal cultivation of alfalfa in fertilization technology.In order to study the effects of fertilizer on alfalfa seedling growth,this research chose four cultivars for production,including Icon,WL-525HQ,Supersonic and WL-903,respectively.The results indicated that average root length,root number,root volume and root surface area at the concentration of 0.1,0.2 and 0.3 times Hoagland nutrient solution were greater than those at the concentration of 0.4 and 0.5 times Hoagland nutrient solution.But average root diameter,root dry weight,stem dry weight,plant height growth rate and dry matter accumulation rate at the concentration of 0.1,0.2 and 0.3 times Hoagland nutrient solution were lower than those at the concentration of 0.4 and 0.5 times Hoagland nutrient solution It showed that the supply of nutrients could not satisfy the nutrients requirement for alfalfa seedling growth at the lower concentration nutrient solution,so in order to absorb more nutrients for growth,the lateral root and secondary lateral roots increased,then average root length and root number increased,as the root volume and root surface area increases followed.However,due to the low concentration of the nutrient solution could not meet the growth of plants,and plant had been in a nutritional deficit condition,therefore it affected plant growth,resulting in stunted plant seedling,less accumulation of dry matter and the decrease of root diameter and root dry weight.Higher concentration of Hoagland nutrient solution could promote root development very well,it had a positive effect on the growth of shoots,such as increasing plant growth rate and dry matter accumulation rate,leading to increase root diameter and dry weight.The effect of nitrogen concentration on seedling growth in alfalfa(cv.:Icon,WL-525HQ,Supersonic,WL-903)was also studied using improvement of Hoagland nutrient solution.The results indicated that application nitrogen had significantly promoted growth for root(taproot diameter and root dry matter),stem(stem diameter,plant height,shoot number,internode number,internode length and stem dry weight)and leaves(leaflet length and width,number and leaf area per plant,leaf dry matter)of alfalfa seeding,and increased plant growth rate.Nitrogen also increased the chlorophyll content,net photosynthetic rate(Pn)and the nitrogen content of plant dry matter.Appropriate nitrogen application could increase dry matter accumulation,the rate of dry matter accumulation and promote greater photosynthetic products transported to the stems and leaves,and increase the ratio of dry matter distribution of stem and leaf.But nitrogen could reduce the number of rhizobia,the root-shoot ratio.Nitrogen application has a significant concentration effect in the promotion of alfalfa seedling growth and dry matter accumulation.Effects was obvious when the nitrogen application below 8 mmol/L;While the treatments did not significantly different at all harvesting when the nitrogen application was 8-12 mmol/L;but effect of nitrogen to promote seedling growth began to decline when the nitrogen application was 12-20 mmol/L(effect of nitrogen to promote seedling gowth in WL-525HQ began to decline when the nitrogen application was 16-20 mmol/L).A significant positive correlation was found between the nitrogen content of dry matter and plant dry weight and leaf Pn.Application of nitrogen could promote the Pn and dry matter accumulation when the nitrogen content of dry matter of alfalfa seedling was lower than 2.82?3.11%,and after reaching to 2.82?3.11%,nitrogen effect was gradually reduced.In summary,alfalfa seedling growth required fertilizer to ensure root and plant grow heathily.However alfalfa seedling need appropriate nitrogen to grow.The effects of nitrogen application to promote growth were obvious when nitrogen content of dry matter was below 2.82?3.11%,but when nitrogen content reached to 2.82?3.11%,the effects were reduced significantly,so too much nitrogen application rate could not be conducive to growth.Therefore,in the system of seasonal planting alfalfa in southern China,we could use 3.0%nitrogen content of dry matter as an reference to evaluate appropriate nitrogen application.