Effects Of Phosphorus Application On Accumulation Of Macroelements And Trace Elements And Root Morphology In Cotton

Understanding the status of nutrient accumulation is essential for achieving high yields of crops,and nutrient accumulation of crops is usually affected by fertilization.The calcareous soil has low available phosphorus content and strong ability to fix phosphorus in Xinjiang.In order to ensure the high yield and quality of cotton,higher phosphorus fertilizer is required.However,excessive phosphorus fertilizer will affect the absorption and concentration of other nutrients in the plant.The objective of this study is to apply phosphorus fertilizer scientifically and reasonably,we set up 5 different phosphorus fertilizer treatments(0,75,150,300,and 450 kg P2O5/hm2)in our field experiment in Manasi County,a typical planting area of cotton in northern Xinjiang.We compared the changes of soil nutrients in cotton seedling stage,flower bud stage and boll stage under different phosphorus application and focused on the absorption and accumulation of some elements(nitrogen,phosphorus,potassium,Fe,Mn,Cu,Zn,Mo)in cotton and root distribution.We also discussed the changes of soil nutrients and the absorption of cotton nutrients under different phosphorus application,and our results provided theoretical basis for guiding the rational phosphate fertilizer application of cotton in Xinjiang.The main results are as follows:1.Increasing the application of phosphorus fertilizer can significantly increase the available phosphorus in the cotton field and the alkaline nitrogen content of the surface soil(0-10 cm).When the amount of phosphorus is<150 kg/hm2,both the available phosphorus and the alkaline nitrogen content of the soil follow the phosphorus application amount.When the amount of phosphorus applied was>150 kg/hm2,the soil available phosphorus continued to increase,but the soil alkaline nitrogen decreased with the increase of phosphorus applied.Moreover,continuous phosphorus application can greatly increase the soil phosphorus pool.Compared with no phosphorus application,the available phosphorus content of 0-5cm,5-10 cm,10-20 cm,and 20-40 cm soil layers in the flower and boll stage in 2017 increased by 13.8%,55.9%,86.2%,and 85.6%,respectively,compared with 2016.In 2018,the available phosphorus content in the soil layers(0-5 cm,5-10 cm,10-20 cm,and 20-40 cm)during the flower bell period increased by 79.7%,150.4%,169.9%,and 283.4%,respectively,compared with 2016.2.Phosphate fertilizer application significantly affected the accumulation of nitrogen,phosphorus,and potassium in cotton and the contents of Fe,Mn,Cu,Zn,and Mo in various organs.when the amount of phosphorus applied was<150 kg/hm2,nitrogen,phosphorus,potassium accumulation increased with the increase of the amount of applied phosphorus.However,when the amount of applied phosphorus was>150 kg/hm2,the dry matter and the accumulation of nitrogen,phosphorus,and potassium increased slowly,and the inhibition phenomenon even appeared in some periods.At the same time,phosphorus application increased the Fe content in the root.Fe,Mn,Mo in the stem and Cu,Zn,and Mo content in the seed gradually decreased with the increase of the phosphorus application.With the increase of phosphorus application,Fe,Zn in the leaves and Fe,Cu,Zn in the flower buds showed a increase and then decrease trend,and the element content reached the maximum when the phosphorus application was in the range of 75-150 kg/hm2.3.Phosphorus application significantly promoted cotton root length.With the increase of phosphorus application(0-150 kg/hm2),the total root length and total root surface area of the root system increased significantly,and phosphorus fertilizer application continued(>150 kg/hm2),but other cotton root characteristics did not continue to increase.Phosphorus application also significantly affected the cotton root distribution,and increased the root length density and root surface area density of each soil layer,especially in the 20-40 cm soil layer.The root length density of each phosphorus treatment increased 1.03-2.50 times.In summary,reasonable application of phosphate fertilizer can significantly increase the absorption efficiency of cotton to nitrogen,phosphorus,and potassium.Regulating the distribution of trace elements in various organs will promote the accumulation of cotton dry matter quality.In addition,excessive application of phosphate fertilizer not only easily causes waste of resources,but also reduces the absorption of nitrogen,phosphorus,potassium and trace elements in cotton.Based on the available soil phosphorus in cotton field,the absorption characteristics of cotton to nitrogen,phosphorus,potassium,and trace elements,and the distribution of roots,under this experimental condition,75-150 kg/hm2 is the optimal amount of phosphorus fertilizer for cotton.