| The side-deep fertilization of rice is an asymmetric local fertilization for rhizosphere of seedlings that fertilizers are applied deep in paddy soil.Most of the researchers analyzed the mechanism of increasing yield and efficiency of side deep fertilization from the agronomic traits of the aboveground part of rice plants.The characteristics of underground roots and soil and their synergistic effects with the aboveground part have not been studied in depth.Therefore,it is of scientific and practical significance for the innovative research of high-yield rice weight loss,green and low-carbon production to further study the root characteristics and nitrogen absorption and utilization characteristics of high-yield rice under side deep fertilization.This field experiment was conducted using rice verities of Nanjing 9108,Fengjing 1606,Yangdao 6,Yangliangyou 6 and Yongyou 2640.In 2020-2021 in Shatou Test Base,Guangling District,College of Agriculture,Yangzhou University,Set 4 kinds of nitrogen fertilizer transportation methods.That is,conventional fertilization with common urea(CF),conventional fertilization with 15%reduction of control released fertilizer(CFCR),side-deep fertilization with 15%reduction of common urea(SDCU),and side-deep fertilization with 15%reduction of control released fertilizer(SDCR)and no nitrogen fertilizer(CK).The effects of different nitrogen fertilizer applications on rice yield,root system and nitrogen uptake and utilization were investigated.The main results are as follows:(1)Different nitrogen applications affected rice yield and its composition.The SDCR treatment significantly increased the yield of the five rice varieties compared to the CF treatment,the CFCR and SDCU treatments decreased but the difference was not significant,while the CFCR treatment yields slightly more than the SDCU treatment.the main reason for the high yield of the SDCR treatment was the increased number of spikes per unit area.There was no significant difference in spikelets per panicle and 1000 grain weight of rice under the four nitrogen treatments.In terms of grain filling percentage,it increased significantly under SDCR treatment in 2020 for Yangdao 6 and 2021 for nanjing 9108,and significantly increased in grain filling percentage under the CF treatment in 2020,while the difference between the remaining varieties was not significant.In terms of rice growth and fertility,compared with CF treatment,SDCR treatment significantly increased the stem tiller number of the five rice varieties,while CFCR and SDCU treatments decreased the stem tiller dynamics.Compared to the CF treatment,SPAD values were significantly higher under SDCR treatment,SPAD values decreased in CFCR treatment and SDCU treatment,and SPAD value was higher under CFCR treatment than under SDCU treatment,SPAD value reached the peak at heading stage.Rice leaf area index,dry matter accumulation and population growth rate were significantly higher under the SDCR treatment than that under CF treatment,while rice leaf area index,dry matter accumulation and population growth rate were lower under the CFCR treatment and SDCU treatment than that under CF treatment and the differences were not significant.In conclusion,controlled-release fertilizer reduced nitrogen by 15%with lateral deep fertilization increased the number of tillers,leaf area index,and leaf SPAD value during the rice growth period,promoted population growth and dry matter accumulation,increased effective panicles,and thus increased grain yield.(2)Different nitrogen applications affected rice root morphology and physiological characteristics.In terms of rice root morphology,compared with the CF treatment,root length,root tip number,root surface area and root volume at different growth stages of the five rice varieties were significantly higher under the SDCR treatment,and lower under the CFCR and SDCU treatments,while root length,root tip number,root surface area and root volume at jointing stage were lower under the CFCR treatment than the SDCU treatment,and higher at heading stage and maturity stage than under that under SDCU treatment.In terms of rice root anatomical structure,compared with CF treatment,SDCR treatment reduced the cortical cross-sectional area,cortical cell layer and root diameter and increased stele diameter in the root system at different growth stages.In terms of root physiological characteristics,compared with CF treatment,SDCR treatment significantly increased root oxidative activity and root glutamate synthase and glutamine synthase activities at different growth stages in rice,while both enzyme activities were reduced but not significantly different under CFCR treatment and SDCU treatment.In conclusion,controlled-release fertilizer reduced nitrogen by 15%promoted rice root growth,improved root structure,and enhanced root vitality,thereby increased absorption and transportation of nutrients,which was beneficial for increasing grain yield of rice.(3)Different nitrogen applications affected soil nutrients and soil enzyme activities in rice root zone.In terms of soil nutrients and soil enzyme activities,compared to the CF treatment,the SDCR treatment increased soil ammoniacal nitrogen and nitrate nitrogen contents at heading and maturity in the 0-5 cm soil layer,while soil ammoniacal nitrogen and nitrate nitrogen contents decreased under the CFCR and SDCU treatments.The SDCR treatment increased the enzyme activities of soil alkaline phosphatase,cellulase,dehydrogenase,sucrase and urease,while the enzyme activities decreased under the CFCR and SDCU treatments.In conclusion,controlled-release fertilizer reduced nitrogen by 15%with lateral deep fertilization increased soil nutrients and soil enzyme activity,improved soil comprehensive fertility,and was conducive to the circulation of nutrients in the system,thus promoting high yield.(4)Different nitrogen applications affected nitrogen uptake and utilization in rice.The total nitrogen accumulation under the SDCR treatment was significantly higher than that under the CF treatment,while the total nitrogen accumulation under the CFCR and SDCU treatments was lower than that under the CF treatment.The accumulation of nitrogen in the main reproductive stages of rice was significantly higher under the SDCR treatment than the other nitrogen treatments,followed by the CF treatment,while the CFCR and SDCU treatments were the lowest and not significantly different.The same pattern was observed for the rate of nitrogen phase uptake,with the nitrogen phase accumulation in the main growth stages was significantly higher under the SDCR treatment than the other nitrogen treatments,followed by the CF treatment,while the CFCR and SDCU treatments were the lowest and not significantly different.Compared to the CF treatment,nitrogen uptake efficiency,nitrogen agronomic efficiency,nitrogen physiological efficiency and biased productivity were the highest under SDCR treatment.While nitrogen uptake and use efficiency decreased under SDCU and CFCR treatments,but nitrogen agronomic efficiency,physiological efficiency and biased productivity were significantly increased.In conclusion,controlled-release fertilizer reduced nitrogen by 15%with lateral deep fertilization increased the nitrogen absorption rate of rice,increased the nitrogen absorption amount at different growth stage and total absorption amount during the stage,thereby improved nitrogen use efficiency. |
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