Effects of Nitrogen Fertilizer on Morphological Development of Alfalfa Root
|School||Nanjing Agricultural College|
|Keywords||alfalfa nitrogen fertilizer root root morphology growth NSC|
Alfalfa (Medicago sativa L.) is the excellent forage for animals. Along with the adjustment of agricultural industrial structure and popularization of grain saving livestock husbandry in China, herbivorous livestock, especially dairy cows, is increasing significantly in southern agricultural regions. However, forage of high quality gap is increasing yearly. In recent years, researchers conducted lots of experiments on alfalfa short term cultivation on winter-fallow fields in southern agricultural regions. They proved that alfalfa could gain high yield. According to the ecological condition and planting system, alfalfa was planned as an after crop in paddy field with techniques of high yield cultivation. But there are certain differences between local environments and alfalfa growing conditions. So, it is of great significance to know that in southern agricultural regions, which kind of alfalfa root can grow better, and how the alfalfa root morphology and nutrients accumulations will change under nitrogen application. The research showed:1. In order to clarify the differences of root morphology, the study on 6 alfalfa cultivars through sand culture experiment showed that, there were significant differences among taproot and root crown diameter, lateral root number and density and root dry matter yield. In 5th leaf age, the root crown diameter of Sidey 10 was 1.41mm. The second lateral root number of Sidey 10 was 29.2. The first lateral root number in 0-2cm of Eureka was up to 63%. The alfalfa cultivar, with special root type which was wide taproot and root crown diameter, plenty of lateral roots and lateral roots gathering below root crown 0～2cm, was superior to be popularized in southern agricultural regions.2. The study was on 6 alfalfa cultivars through pots and winter-fallow field experiments. The purpose was to investigate root morphology changes and nutrients accumulations under different nitrogen application. The results indicated that nitrogen fertilizer could wide taproot diameter, root crown diameter, increase root dry matter yield, and move up first lateral root position significantly. These root traits were effectively correlated with shoot dry matter yield. Under the nitrogen application of 160 kgN·hm-2, taproot and root crown diameter were 7.74mm and 9.28mm, faster than the growth of non-nitrogen application by 22% and 16% at the early blooming stage. The first lateral root emerged below root crown 0.40cm, moving up by 0.06cm of non-nitrogen application. The root dry matter yield was 3.84g per plant, increasing by 30% of non-nitrogen application. There were similar performances under the nitrogen application of 80 kgN·hm-2. Meanwhile, nitrogen content in alfalfa plant was significantly increasing with the nitrogen application, especially at treatments of 80 kgN·hm-2 and 160 kgN·hm-2. The non-structure carbohydrate (NSC) in alfalfa root decreased firstly and increased then. From early blooming stage to full blooming stage, the NSC accumulation under 80～160 kgN·hm-2 was higher than that under non-nitrogen treatment.All results above revealed that, such root traits, which were taproot and root crown diameter, lateral root number, the density of first lateral root below root crown 0～2cm, were important for alfalfa to be popularized in southern agricultural regions. Nitrogen fertilizer could significantly promote taproot and root crown diameter, first lateral root position and root dry matter yield. Also, under nitrogen application, nitrogen in alfalfa plant was increasing remarkably; the NSC in alfalfa root was accumulated heavily from early blooming stage to full blooming stage.