通常栽培的豆科作物菜豆、豇豆、花生、大豆、三叶草、苜蓿、苕子、紫云英等,或多或少能自然形成一些菌瘤,但这些菌瘤的固氮能力和培肥土壤的作用均有不同程度的局限性.因此,对饲用和绿肥用的豆科作物实行根瘤菌接种,是一项很好的增产措施.根瘤菌一方面侵入植物根部结瘤共生,一方面还能在土壤中营独立生活.随着土壤条件不同,其存活表现非常悬殊.土壤条件愈坏,其含菌量愈少.土壤过酸、过碱,水分过高,干旱或缺少植物需要的营养物质等,都是致使根瘤菌减少的因素.据测定,江苏盐土(二级以上)和花碱土(C1~-0.6%)都没有什么根瘤菌.即使种植豆科作物多年的地区,土壤中有一定数量的根瘤菌,也多处于衰退状况,固氮能力和侵染结瘤力都不如人工筛选的根瘤菌强. Commonly cultivated leguminous crops such as beans, cowpea, peanut, soybean, clover, alfalfa, razor clam, astragalus, etc. can form more or less naturally occurring bacterial tumors, but the ability of these bacteria to fix nitrogen and fertilize the soil Have different degrees of limitations.Therefore, the introduction of rhizobia for forage and green manure crops Rhizobium inoculation, is a good yield measures.N rhizobia on the one hand invade the plant root nodulation symbiosis, on the one hand but also in the Soil camp independent living. With the different soil conditions, their survival performance is very poor. The worse the soil conditions, the less bacteria. Soil over-acid, over-alkali, water is too high, drought or lack of nutrients needed by the plant , Are the factors that lead to the reduction of rhizobia.It is determined that there is no rhizobia in Jiangsu salt soil (Grade 2 or above) and theaerobic soil (C1 ~ -0.6%) Even if the leguminous crops are planted for many years, there is a certain amount of soil Of rhizobia, but also more in recession, nitrogen fixation ability and infection of nodulation are not as good as artificial selection of rhizobia strong.