Effect of Arbuscular Mycorrhizal Fungi on Nutrient Uptake and Onion Yield in a Saline Soil at Field Conditions

Mycorrhizal fungi are important symbionts in plants and have key role in nutrients acquisition and enhancing plant tolerance against environmental steresses. This study was conducted to evaluate effect of field inoculation of onion with arbuscular mycorrhiza fungi on yield and nutrients uptake in a saline soil during 2004 and 2005 at Khosroshahr Agricultural Research Station. Onion seedlings were inoculated with four speices of Glomus: G. etunicatum, G.versiforme, G.mosseae and G. intraradices in the nursery. Seedlings at about 20 cm height were transplanted into field and cultivated in two groups: 1- without phosphorus and 2- with one half of the recomended phosphorus (50 kg P.ha -1). At the planting early in spring, soil EC of the experiment site was 7.26 and 5 dS/m in the first and second year; EC of the irrigation water was 5 dS/m. At the end of growth, onion bulb yield and concentrations of N, P, K, Na, Cl, Ma, Zn, Cu in the bulbs were measured. Combined data analysis for two years showed that there is significant difference between the treatment effects on yield and P, Na, Cl, Zn, Cu concentrations and total uptake of N, P, K, Zn and Cu in the bulbs (p<0.01) and total uptake of Na, Cl and Mn (p<0.05). Significantly greater yield of onion bulb was obtained from inoculation with arbuscular mycorrhiza fungi in both years. The highest yield resulted from inoculation with G. etunicatum (32.3 t/h) and G. versiforme (30.76 t/h) with the application of 50 kg P.ha -1. Non-inoculated treatment without P-fertilizer produced the lowest yield of 12.6 t/ha. Bulb Na-concentration in G. etunicatum inoculated onion without P-fertilizer reached to the lowest level (0.323 percent in dry matter) and in non-inoculated onion was the greatest (0.476 percent in dry matter). Bulb Cl-concentration in G. mosseae inoculated onion with one half of the recommended phosphorus and G. etunicatum inoculated onion without P-fertilizer reached to the lowest levels (0.778 and 0.791 percent in dry matter, respectively) and in non-inoculated onion was the greatest (1.143 percent in dry matter). Evidently inoculation with mycorrhiza led to greater yield and lower Na and Cl content in the onion bulbs.