Effects Of Enhanced Ammonium Nutrition On Growthand Microstructure In Cotton

Nitrogen fertilizer is an important nutrient element for crop growth and development.Inorganic nitrogen in soil mainly exists in the mixture of ammonium nitrogen?NH₄⁺-N?and nitrate nitrogen?NO₃^--N?.Proper ratio of ammonium nitrogen?NH₄⁺-N?and nitrate nitrogen?NO₃^--N?is beneficial to increase crop yield and improve nitrogen use efficiency.Mixed nitrogen nutrition is also called ammonium-increasing nutrition?Enhanced Ammonium Nutrition,EAN?,which can increase ammonium by changing the ratio of ammonia-nitrate and adding nitrification inhibitor?dicyandiamide,DCD?.Cotton is an important economic crop in the world;however there are few researches on increasing ammonium nutrition in cotton growth,physiology,microstructure and yield.Therefore,in this paper,the reaction of cotton seedlings to NH₄⁺/NO₃^-in different growth periods was discussed and the optimum application effect of NH₄⁺-N/NO₃^--N was investigated in hydroponic culture tests?NH₄⁺-N/NO₃^--N ratio of 0/100,25/75,50/50,75/25 and 100/0,respectively?.The effects of different DCD dosage on cotton physiology,structure and yield were determined and appropriate dosage of DCD was selected in field experiments with conventional fertilization?CK1,240kg/hm² of nitrogen;C1.5,240kg/hm² of nitrogen+1.5%DCD;C3,240kg/hm² of nitrogen+3%DCD?and nitrogen reduction fertilization?CK2,180kg/hm² of nitrogen;D1.5,180kg/hm² of nitrogen,+1.5%DCD;D3,180kg/hm² of nitrogen+3%DCD?.It could provide theoretical basis for the development and utilization of new fertilizers.The main research results were as follows:1.Morphological characteristics:different NH₄⁺-N/NO₃^--N ratio had different effects on crop growth under the condition of hydroponic experiment.With the increase of NH₄⁺concentration in ammonium nutrient solution,the plant height,stem diameter and leaf area of cotton showed the trend of increasing first and then decreasing.When NH₄⁺-N/NO₃^--N ratio was higher than 50%,the growth of cotton seedlings was obviously inhibited.When NH₄⁺-N/NO₃-N ratio was less than or equal to 50%,it was beneficial to the shoot growth of cotton seedlings.The increase of ammonium nutrition promoted the cotton plant height,stem diameter and leaf area under the condition of field experiment,among which the promotion effect of conventional fertilization with 1.5%DCD and nitrogen reduction fertilization with DCD was more obvious than control.2.Physiological characteristics:different NH₄⁺-N/NO₃^--N ratios had different promoting effects on cotton seedlings under hydroponic conditions at different growth stages,among which the NH₄⁺-N/NO₃^--N ratio of 75/25 had a significant promoting effect on chlorophyll content,soluble sugar and soluble protein content of cotton seedlings.The content of chlorophyll,soluble sugar and soluble protein in cotton was increased by adding DCD in the field experiment,but there was no significant difference and the dose effect was not significant among various treatments.3.Microstructure:different ammonium nitrate ratios had different promoting effects on the roots,stems and leaves of cotton seedlings under hydroponic condition.Among them,when NH4+/NO3-ratio was 25/75,it had an obvious promoting effect on root development.When NH4+/NO3-ratio was 50/50,it had an obvious promoting effect on phloem and xylem of stem.When NH4+/NO3-ratio was 75/25,it had an obvious promoting effect on xylem and phloem of leaf pulp and vein.The treatment of conventional fertilization combined with DCD had different promoting effects on the leaf pulp,leaf vein,leaf stalk and bell stalk of cotton under the field condition,and the promoting effect of 1.5%DCD was significant.Under the treatment of nitrogen reduced fertilization,the structure of all organs of cotton became more developed with the increase of DCD dosage,but the dose effect was not significant.4.Soil nitrogen content:there was no significant change in ammonium nitrogen content with the increase of soil depth in the 0-40cm soil layer,while nitrate nitrogen content and total nitrogen content decreased with the increase of soil depth.The addition of DCD treatment could improve the content of ammonium nitrogen and reduced the accumulation of nitrate nitrogen in soil.With the increased of DCD,the content of ammonium nitrogen increased gradually,while the content of nitrate nitrogen decreased gradually.It indicated that the inhibitory effect on nitrate nitrogen was significant by adding DCD treatment.5.Dry matter accumulation:with the increase of NH₄⁺concentration in ammonium enriched nutrient solution under the condition of hydroponics,the total dry matter mass,root dry matter mass,stem dry matter mass and leaf dry matter mass all showed a trend of rising first and then falling,and reached the maximum when NH₄⁺/NO₃^-ratio was 75/25.The dry matter quality of Nongda Cotton 601 was significantly improved by 1.5%DCD treatment under the condition of conventional fertilization.Dry matter quality increased gradually with the increase of DCD dosage under the condition of nitrogen reduction fertilization,but the difference in dry matter quality was not obvious.6.Yield and composition:the treatment of conventional fertilization combined with1.5%DCD had a significant effect on the yield increase of Nongda Cotton 601.Under nitrogen reduction fertilization,DCD treatment both had a significant yield increase compared with the treatment without DCD addition,but the DCD dosage had no significant difference in yield.To sum up,the effect of NH₄⁺/NO₃^-ratio of 25/75 or 50/50 on the morphological characteristics of cotton seedlings was more significant in the early growth stage of cotton,and the effect of NH₄⁺/NO₃^-ratio of 75/25 on the physiological characteristics of cotton was more significant when the cotton was transferred from vegetative growth to reproductive growth.Field experiments showed that conventional fertilization?240kg/hm²?combined with 1.5%DCD significantly promoted the increase of dry matter quality and yield of cotton,and nitrogen reduction fertilization?180kg/hm²?combined with 1.5%DCD significantly increased yield,indicating that conventional fertilization and nitrogen reduction fertilization combined with 1.5%DCD could be used in production,but it needs to be further verified.