不同施氮水平下接种根瘤菌对苜蓿固氮效能及种子生产的影响

Effects of different nitrogen levels on nitrogen fixation and seed production of alfalfa inoculated with rhizobia

设置田间小区试验和沙培试验,采用15 N自然丰度法测定不同施氮水平下、不同方式接种根瘤菌对紫花苜蓿固氮效能、生长和种子产量的影响。结果表明,在50kg/hm2低施氮量下,接种根瘤菌能增加苜蓿的根瘤数量和根瘤重量,苜蓿固氮率、固氮量均达到了最高,分别为(77.8±0.508)%和(452.51±2.568)kg/hm2。接种根瘤菌有效促进了苜蓿的生长,提高了地上部干物质积累,增加了有效分枝数、荚果数及种子产量,种子产量增幅平均达(59.7±0.118)%,显著高于不接种、不施氮和其他施氮处理。而施氮量超过50kg/hm2,则会抑制根瘤菌结瘤,引起苜蓿固氮率、固氮量下降。随着施氮量增加,根瘤菌促进苜蓿植株生长的效应明显减弱,造成生物量和荚果数减少,种子增产幅度降低。比较秋播拌种和春季返青追施2种不同的根瘤菌接种方式,以秋播拌种根瘤菌结合施氮量50kg/hm2时的增产最为显著。秋播拌种根瘤菌的生物固氮百分率和固氮量与苜蓿种子产量呈显著正相关。

Field plot and sand pot experiments were carried out to study the effects of four different nitrogen fertilizer levels（0,50,100,150 kg/ha） and two ways of inoculating rhizobia（soaking seeds with rhizobia in autumn and furrow inoculating rhizobia in spring） on the nitrogen fixation ability,growth characteristics and seed yield of alfalfa by using a 15N natural abundance method.The field experiments were located at the grassland ecological research station in Hutubi County of Xinjiang Agricultural University during the growing seasons 2009 to 2010.The nodule numbers and nodule fresh weight were significantly improved by inoculating rhizobial strain ACCC17544,and attained the maximum percentage and amount of nitrogen fixation（77.8±0.508）% and（452.51±2.568） kg/ha respectively under the lower level of 50 kg/ha nitrogen application.Also,inoculating rhizobia promoted growth,increased above ground dry matter accumulation,number of branches,number of pods and seed yield of alfalfa.The seed yield obtained had an average increase rate of（59.7±0.118）% that was significantly more than those in uninoculated,no nitrogen fertilization and other nitrogen rate treatments.Nitrogen application above 50 kg/ha inhibited nodulation and the percentage and amount of nitrogen fixation were reduced.With increasing amounts of nitrogen fertilizer,the inoculating rhizobial efficiency for improving alfalfa growth were obviously weakened,and the biomass,number of pods,and extent of yield increase were reduced.Soaking seeds with rhizobia in autumn combined with nitrogen application of 50 kg/ha was the best combination for increasing seed yield in the field plot experiments.There was a significant positive relationship between the amount of rhizobial nitrogen fixation and seed yield.