NO_3^--N/NH_4^+-N配比对紫花苜蓿根系生长及固氮特性的影响

Effects of NO_3^--N/NH_4^+-N ratios on root growth and nitrogen-fixation characteristics of alfalfa

【目的】为了探明NO_3^--N/NH_4^+-N不同配比下紫花苜蓿根系生长及固氮特性,了解NO3--N与NH4+-N的最适配比,提高紫花苜蓿外源氮利用效率.【方法】室外防雨网室内,以‘甘农3号’为研究材料,采用盆栽营养液沙培法,在氮素水平210mg/L下,设NO3--N和NH4+-N的7个混合配比(1∶7、1∶3、3∶5、5∶5、5∶3、3∶1、7∶1),测定处理后紫花苜蓿各生育期根系相关指标.【结果】全生育期内,不同氮素形态配比下(NO_3^--N/NH_4^+-N)紫花苜蓿的根系生物量、根系总长度和根表面积均在NO_3^--N/NH_4^+-N配比为5∶3处理下显著高于其他处理;根瘤数、根瘤质量和固氮酶活性在紫花苜蓿生长的前中期(苗期和现蕾期)均在NO_3^--N/NH_4^+-N配比为1∶7处理下最大,而中后期(盛花期、结荚期和成熟期)在NO_3^--N/NH_4^+-N配比5∶3处理下达到最大值.整个生育期,各处理下紫花苜蓿的根系生物量差异显著,而根系总长度、根表面积、根瘤数、根瘤重在前中期差异显著,而后期差异不大.【结论】NO3--N和NH4+-N均能促进紫花苜蓿各时期根系生长,但二者混合使用且NO_3^--N/NH_4^+-N比例为5∶3时,紫花苜蓿根系生长最好,肥料报酬率高.与此同时,紫花苜蓿自身固氮能力也最强,对氮素的利用率达到最高.

【Objective】To ascertain the root characteristic and nitrogen fixation characteristics of Medi cagosativa（cv.‘Gannong No.3＇）and find out the optimum ratio,improving the utilization efficiency of exogenous nitrogen.【Method】Under the condition of nutrient solution and the nitrogen level of 210mg/L（pure nitrogen）,the effect of 7ratios of NO_3^--N/NH_4~＋-N（1∶7,1∶3,3∶5,5∶5,5∶3,3∶1,7∶1）on root characteristics and nitrogen fixation characteristics of the alfalfa were studied outdoors during the whole growth stage by sand culture method,determination of related parameters of the growth period of the root system after processing.【Result】The root biomass,root total length and root surface area of alfalfa at ratio of 5∶3treatment were all significantly higher than those of other treatments during the whole growth stage.The maximum of nodule number,nodule weight and nitrogenase activity were 1∶7treatment before the mid-stages（seeding and budding）and 5∶3treatment after the mid-stages（flowering,seed podding and maturing）.During the whole growth stage,each treatments of alfalfa root biomass has significant differences,but root total length,root surface area,nodule number and nodule weight has significant differences before the midstages,and their has no significant differences after the mid-stages.【Conclusion】NO_3-^-N and NH_4~＋-N can promote alfalfa root growth each time,but both mix proportion and NO_3^--N/NH_4~＋-N is 5∶3,alfalfa root growth,the best fertilizer return rate is high.At the same time,under the ratio of alfalfa and nitrogen fixation ability is strongest,reached the highest utilization rate of nitrogen.