Study On The Mechanism Of The Interaction Between Water And Phosphorus On The Root Morphology And Phosphorus Efficiency Of Cotton

Enhancing the P use-efficiency of cotton is crucial not only for sustainable utilization of P resouce in China,but also for the requriment of both the cotton industry and the farmers to save their cost in lint production by reducing P fertilizer application rate in Xinjiang.This paper is target on improving P use-efficiency of cotton in Xinjiang cotton-zone where the cotton is grown by a typical integrated model called mulched drip-irrigation,and based on the frontier theory of interaction between root and soil biological nutrient turnover and utilization control as guidance,to the problem of low efficiency of utilization of soil phosphorus resources in cotton planting system of drip irrigation which is special in Xinjiang as the object.A root box experiment was conducted to investigate effects of water phosphorus interaction on root morphology and phosphorus efficiency in cotton in 2015 and 2016,the experiment setting different water and phosphorus supply gradient,and monitoring the spatial and temporal variation characteristics of cotton root architecture and soil moisture continuously,the objectives of this paper are:to uncover the dynamic characteristics of soil phosphorus,response mechanism of cotton root morphology and architecture,the key process of efficient activation and utilization of soil phosphorus by the interaction of the root system with the support of the root system and its synergistic mechanism,to clarify the play of cotton the activation of water and phosphorus utilization of soil phosphorus accumulation regulation of biological potential.The results indicated that:?1?The application of P could increase the content of available P in soil significantly,but the effect of soil moisture on soil available phosphorus was limited.Soil water treatment had no significant effect on the content of available P in soil,so the increase of water content could not promote the desorption of soil fixed phosphorus.However,the content of available P in soil increased obviously with the increase of P application rate,especially under the condition of 1 g P₂O₅/kg,the content of soil available P increased to more than 40 mg/kg,and reached a high level.As a result,the amount of phosphate fertilizer is the key means to adjust the soil phosphorus deficiency.?2?The soil moisture content,spatial and temporal variation showed significant difference under different water treatments.The content of soil moisture was higher under adequate water supply treatment,but the soil moisture content in different regions showed different trends with the passage of time:in the start of the water supply,the soil moisture mainly distributed near the dripper,and presented the distribution characteristics of the oval,then soil moisture gradually fall down,but compared with sufficient water supply,the soil water content was significantly decreased under 35 cm soil,water supply after 44 h than 22 h under water shortage treatment,while the water content of adequate water supply treatment had no significant difference under different time in this area.?3?The water content has a decisive effect on the total root length of cotton.The cotton root length is larger under water shortage treatment than water adequate supply particularly under P deficiency;but under water adequate supply conditions,the cotton root length showed a increased trend with the increase of the soil phosphorus content,while there was no response of root length almostly for phosphorus supply under the condition of water shortage.It suggested that the effects of the moisture content and distribution had the more dominant position to cotton root length,relative to the amount of phosphorus supply.?4?The water and phosphorus showed a significant interaction on the growth of cotton roots,the cotton root distribution in soil is longer and deeper under water stress especially under P deficiency;the cotton root length showed a increased tread with the increase of the phosphorus content under adequate water supply treatment,while root length was no response to the P supply almost under water stress conditions.It suggested the water is the first for cotton root length growth,and only in the premise of adequate water supply,the phosphorus supply can play the role of promoting on cotton root length.?5?The hyphae density showed a trend of higher in shallow soil than the deep layer in the soil profile,and there was a close synergistic relationship between hyphae and roots of cotton plant.The growth of cotton hyphae was restricted by the increase of phosphorus content in soil,but sufficient water supply could promote hyphae growth significantly.Hyphae growth was most suitable in the range of soil available phosphorus 15-20 mg/kg and soil water content in 0.4-0.6 m³/m³ range.?6?The suitable water and phosphorus supply is more conducive to cotton growth.Compared with the water supply,the effects of soil available phosphorus content on the level of phosphorus absorption of cotton is bigger,and the enhancement effects of water supply for the cotton phosphorus absorption only under suitable phosphorus conditions,so considering the utilization ratio of phosphate fertilizer meanwhile,a suitable water and phosphorus supply for cotton was most favorable for phosphorus absorption.Combining the effects of water phosphorus interaction on the cotton root length and hyphae density in soil,the optimum soil water and phosphorus range was 0.3-0.4 m³/m³and 15-22 mg/kg,respectively.These results indicated that,the appropriate water and phosphorus treatment can improve the growth of cotton root and hyphae,and stimulate the physiological responses of cotton root,thereby strengthening the activation and absorption capacity of cotton to soil phosphorus,and then improve the utilization rate of phosphate fertilizer.