Soil salinity is deleterious for the growth and biological N₂ fixation of alfalfa (Medicago sativa L.), but nitrogen fertilization has been beneficial in some cases. This study was conducted to investigate the potential benefit of N fertilization on alfalfa growth and N₂ fixation under saline conditions. Solutions of sodium chloride (NaCl) and hydrous calcium chloride (CaCl₂.2H₂O) were added to induce EC_e (electrical conductivity of the saturated paste extract) targeted at 0.5, 5, 10, and 15 dS m⁻¹ in a sandy loam soil. ¹⁵N-labeled ammonium nitrate (NH₄NO₃) was added to the soil at 30, 60, and 120 mg N kg⁻¹ soil. Alfalfa shoot and root dry weights, root nodule counts, shoot total nitrogen (N), potassium (K) and sodium (Na⁺), and the amount of N derived from air (%Ndfa) were determined. Shoot Na concentration increased, and plant biomass, shoot N and K concentration, root nodules, and nitrogen Ndfa decreased as soil salinity increased. At all salinity levels, the highest plant biomass, shoot total N content, and K/Na ratio were recorded at 120 mg N kg⁻¹ soil. Root nodulation and %Ndfa were highest at 60 mg N kg⁻¹ soil under nonsaline conditions while under saline conditions, the highest nodulation and %Ndfa were recorded at 30 mg N kg⁻¹ soil. Plant biomass, nodule number, and %Ndfa were greater in the third cut than in the first cut. Addition of nitrogen fertilizers seemed to have a positive effect in alleviating salt stress in alfalfa and maintaining shoot biomass production, but N fertilization may limit the plant’s ability to fix atmospheric N.

土壤盐度是有害的生长和生物Ñ ₂苜蓿（固定苜蓿L.），但氮施肥已经在某些情况下是有益的。进行这项研究以研究在盐分条件下施氮对苜蓿生长和N ₂固定的潜在好处。加入氯化钠（NaCl）和含水氯化钙（CaCl ₂ .2H ₂ O）的溶液，以在0.5、5、10和15 dS m ^-1中诱导EC _e（饱和糊状提取物的电导率）。沙壤土。¹⁵ N标记的硝酸铵（NH ₄ NO ₃）分别以30、60和120 mg N kg ^-1的土壤添加到土壤中。测定苜蓿芽和根的干重，根瘤数，芽总氮（N），钾（K）和钠（Na ⁺）以及源自空气的氮含量（％Ndfa）。随着土壤盐分的增加，地上部Na浓度升高，植物生物量，地上部N和K浓度，根瘤和氮Ndfa含量降低。在所有盐度水平下，在120 mg N kg ^-1土壤中均记录到最高的植物生物量，芽总N含量和K / Na比。在非盐碱条件下，根结瘤和％Ndfa最高于60 mg N kg ^-1，而在盐碱条件下，最高结瘤和％Ndfa最高记录于30 mg N kg ^-1泥。第三次切割的植物生物量，根瘤数和％Ndfa大于第一次切割。氮肥的添加似乎对缓解苜蓿的盐胁迫和维持枝条生物量的生产具有积极作用，但氮肥的施肥可能会限制植物固定大气氮的能力。