Effects Of Nitrogen Supply Level And Nitrogen Fertilizer Forms On Cotton Growth And Nutrient Absorption

In order to explore the effects of different nitrogen forms and nitrogen levels on the growth and nutrient absorption of cotton,the cotton cultivars of Xinluzao 45 and Xinluzao 48 were selected as experiment materials.The differences of growth indexes under six nitrogen levels in two cotton cultivars were studied by hydroponic experiment.The root-box experiment was used to explore the difference in response of growth indexes of two varieties of cotton to different forms of nitrogen fertilizer by setting treatment of the no nitrogen fertilizer,CO（NH₂）₂,（NH₄）₂SO₄and Ca（NO3）2.The main results are as follows:（1）Hydroponic experiment:The dry matter quality,nitrogen,phosphorus and potassium accumulation,total root length,root surface area,nitrogen uptake efficiency of cotton in two varieties showed a quadratic function that increased first and then decreased with the nitrogen levels.In addition,the above determination indexes all reached the maximum at the nitrogen level of 17.5 mmol/L.The root-crown ratio and nitrogen utilization efficiency of the two varieties of cotton decreased with the increase of nitrogen level,and tended to be stable at the nitrogen level of 15 mmol/L.The determination indexes of Xinluzao 48were better than those of Xinluzao 45 under six levels of nitrogen supply.Therefore,the growth indexes of the two varieties of cotton were significantly improved under the reasonable nitrogen supply level,but the lower or higher level of nitrogen application was not conducive to the increase of cotton growth indicators.Under the same nitrogen supply level,the cotton cultivars of Xinluzao 48 has stronger growth ability than Xinluzao 45.（2）Root box experiment:The contents of alkali-hydrolyzed nitrogen,organic matter,nitrate nitrogen and available potassium in soil could be significantly increased by applying three forms of nitrogen fertilizer.The contents of alkali-hydrolyzed nitrogen in Ca（NO₃）₂ treatment was significantly higher than that in（NH₄）₂SO₄ and CO（NH₂）₂ treatment by 6.15%and 13.1%,respectively.And the soil available potassium content was the highest with（NH₄）₂SO₄ treatment,which was 3.45%higher than that under Ca（NO₃）₂ treatment.Different forms of nitrogen fertilizer treatment had no significant effect on soil ammonium-N,nitrate-N and available phosphorus content.The p H value of rhizosphere soil treated with Ca（NO₃）₂ was significantly higher than that treated with（NH₄）₂SO₄.Different forms of nitrogen fertilizer could increase the biomass,nutrient content and root morphological parameters of cotton in two varieties.In comparison to other two forms of nitrogen fertilizer,the treatment of Ca（NO₃）₂ supply that was more helpful to promote the increase of biomass,nitrogen and potassium accumulation of Xinluzao 45 and Xinluzao 48.However,the accumulation of phosphorus in the（NH₄）₂SO₄ treatment was higher than that of other two nitrogen fertilizer forms treatment.The root length,root volume and surface area of Xinluzao 45and Xinluzao 48 with Ca（NO₃）₂ treatment are higher than those of the other two nitrogen fertilizer treatments.Under the three forms of nitrogen fertilizer,the growth indexes of Xinluzao 48 were still higher than Xinluzao 45.Therefore,the selection of appropriate nitrogen fertilizer forms is conducive to better promote the increase of various growth indicators of cotton,thus ensuring high cotton yield.Moreover,the response of Xinluzao 48 to different nitrogen fertilizer forms is higher than Xinluzao 45.In summary,different nitrogen supply levels and nitrogen fertilizer forms had different effects on the growth indexes of cotton.In the soil of this experiment,the application of nitrate nitrogen is more helpful to promote the growth and development of cotton.In agricultural production,the cotton cultivars of Xinluzao 48 is more suitable for farmland extension than Xinluzao 45.And selecting the appropriate nitrogen form under the reasonable amount of nitrogen application rate can not only increase the basic soil fertility,but also promote the growth of cotton roots,and then improve the ability of root absorption and utilization of nutrients,increase the dry matter mass of cotton,so as to achieve high cotton yield.