| Potassium is one of the essential nutrients for crop growth and development and can significantly improve crop yields,quality,and stress resistance.However,potassium ions are easily fixed by the soil into non-exchangeable potassium,which reduces potassium availability and crop absorption.Potassium ions can also replace the polyvalent cations(Ca2+,Mg2+)in the soil aggregate structure,causing soil compaction.To achieve higher crop yields and incomes,farmers use large amounts of potassium fertilizer for long periods,causing resource waste,soil quality degradation,and other problems.By controlling the coating thickness,the potassium ions slow release of controlled-release potassium chloride can be synchronized with the absorption of crops,to ensure the availability of potassium ions in the soil,meet the needs of crops for potassium in the later stage,and significantly improve the potassium use efficiency（KUE）.At the same time,after coating with potassium chloride,direct contact between potassium ions and soil is reduced,while displacement with multivalent cations is reduced,stabilizing soil aggregates and improving soil quality.This study focused on the mechanism of soil potassium supply and efficient utilization of crop nutrients by CRK in wheat/corn rotation positioning experiments.Through the correlation analysis of multiple soil parameters,the impact of CRK on soil nutrient supply levels was clarified;the physiological and biochemical mechanisms of CRK promoting crop root growth and photosynthesis were revealed using in situ root scanning and enzyme-linked immunosorbent assay techniques;combined with soil high-throughput sequencing and metabolomics analysis,the comprehensive regulation mechanism of CRK on microbial community and functional metabolites in root zone microdomain was clarified.The main results of the study were as follows:（1）Explored the impact of CRK application on soil nutrient supply intensity,meeting the nutrient demand of crops throughout their entire growth period.The nutrient release of CRK in the maize and wheat seasons showed an S-shaped curve in three phases:the early slow-release phase,the middle accelerated-release phase,and the late slow-reduction phase.The cumulative release reached more than 80%and 90%after 110 and 210 days,respectively.Which was synchronized with the nutrient demand of crops,and met the demand for potassium in the middle and late stages.In the critical period of maize nutrient demand,compared with traditional potassium chloride（K）treatment,blending 50%controlled-release potassium chloride and 50%soluble potassium chloride（BBF）and CRK treatments significantly increased soil available potassium content by 21.2%and 15.1%,soil water soluble nitrogen content by 4.3 times and 4.1 times,soil nitrate nitrogen and organic matter content also significantly increased.Therefore,CRK provides the most stable nutrient levels during the crop growth period and sufficient nutrient conditions for the growth and development of crops.（2）The significance of CRK in improving crop photosynthesis,plant bleeding rate,and nutrient content in bleeding solution has been clarified,confirming its significant role in promoting crop nutrient absorption,crop yield,and KUE.Compared with K treatment,the photosynthetic rates of CRK and BBF treatments were significantly increased by 29.5%and36.1%,respectively,and the bleeding sap rate of CRK treatment was significantly increased by 19.5%and 47.5,and the electrical conductivity of bleeding sap was significantly increased by 30.6%and 33.3%,respectively.The average KUE for maize of CRK and BBF treatments increased significantly by 5.7 percentage points and 9.3 percentage points,the average KUE for wheat increased significantly by 6.0 percentage points and 9.1 percentage points;the average yield of maize increased significantly by 7.2%and 14.0%,and the average yield of wheat increased significantly by 7.9%and 11.7%;the average net profits of maize increased significantly by 9.1%and 18.9%,and the average net profits of wheat increased significantly by 6.7%and 17.7%,respectively.Compared to K treatment,when reduced by 1/3 by applying CRK treatment still maintained stable or increased crop yields.（3）Clarified the impact of CRK on the spatial distribution of crop roots and changes in endogenous hormones,improving crop stress resistance and nutrient absorption characteristics.The CRK significantly optimized the spatial distribution of wheat roots in the soil,compared with the K treatment,the root volume,surface area,and average diameter of BBF treatment increased by 80.2%,38.8%,and 29.6%,respectively,and the root IAA content increased by 19.5%,which significantly promoted the growth of wheat roots;the puncture strength and bending resistance of CRK treatment were significantly increased by 11.2%and12.8%,and the puncture strength and bending resistance of BBF treatment were significantly increased by 12.4%and 13.0%,respectively,which could effectively improve the lodging resistance of maize straw;CRK and BBF treatments increased the wheat leaf area index by15.2%and 30.3%,while the IAA content in leaves of CRK and BBF treatments increased by11.9%and 14.0%,which significantly increased the wheat photosynthetic area and the accumulation of photosynthetic products and improved crop yield.（4）The mechanism of CRK on the root zone microenvironment has been explored,revealing its regulatory mechanism on functional microorganisms and key metabolites.Compared to K treatment,BBF treatment improved the relative abundance of Arthrobacter,Streptomyces,Sphingomonas,Limnobacter,and Marmoricola,which are involved in soil nutrient metabolism and nitrogen and potassium cycles;the relative abundance of Pseudomonas,Pantoea,Bacillus,and Exophiala related to protein decomposition,glucose metabolism,and potassium ion absorption in crop roots of BBF treatment was increased;CRK and BBF treatments can significantly enrich the processes related to energy and nutrient metabolisms,such as glucose,flavonoid,and amino acid metabolic pathways,significantly increased 1-Methyl-2-nitro-3-（（tetrahydrofuran-3-yl）methyl）guanidine content 25.1%and49.5%;the content of Deoxycholic acid 3-glucuronide was significantly increased by 22.6%in BBF treatment;the main enrichment pathway in roots of CRK and BBF treatments was related to crop metabolism,nutrient metabolism,and stress resistance,the content of 3-Hydroxyanthranilic acid was increased by 14.3%and 18.3%,and the content of Integerrimine was increased by 19.8%and 25.1%,the content of 2’-Deoxymugineic acid was increased by16.1%and 16.5%,and the content of Tyramine glucuronide was increased by 17.3%and18.4%.There was a significant positive correlation between the composition of functional microorganisms related to soil nutrient conversion and the key metabolites related to crop energy metabolism and nutrient metabolism in the metabolome pathways,revealing the molecular mechanism of CRK improving the root zone microenvironment and promoting efficient utilization of crop nutrients.By exploring the application and efficiency-enhancing mechanism of controlled release potassium chloride in the wheat/corn rotation system,the mechanism of slow and controlled release potassium chloride to increase soil potassium supply intensity,optimize the composition of functional microorganisms and key metabolites in the root zone,promote the spatial distribution and growth of crop roots,improve crop photosynthesis and nutrient absorption and transformation ability,and increase crop potassium use efficiency and yields has been clarified.It provides a theoretical basis and technical support for the promotion and application of controlled-release potassium chloride. |
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