effect of zinc and salicylic acid foliar application on quantitative and qualititative characteristics of soybean under deficit irrigation conditions

introduction soybean (glycine max (l.) merrill) is a leguminous annual crop belonging to the fabaceae family, that because an important source of food containing 20 to 28 grain oil percent and high protein is the most important oilseed of worldwide interest. recently, cultivation of this plant is considered as a valuable oil plant in crop rotation. drought, salinity, heat and freezing are environmental conditions that cause adverse effects on the growth of plants. water deficit more than other stresses limits the growth of crops. yield of soybean decreased due to drought stress. the consumption of fertilizers increases the quality of crops. according to the findings of yasari and vahedi (2012) use of zn in soil and foliar application has an increasing effect on the percentage and the amount of oil and protein in soybean product. the role of salicylic acid (sa) is reducing the effects of environmental stresses. it appears that water stress impairs plants and zinc alleviates water stress injuries. thus, the purpose of this study was to evaluate the effect of water stress, zinc and salicylic acid foliar application on oil and grain protein percentage and their relation with oil and protein yield of soybean. materials and methods this study was carried out in the agricultural garden of lorestan-iran, in 2013. the meteorological data of the region are representing in table 2. the soil was clay-loam texture (table 1). the experiment was performed using split factorial in a randomized complete block design with four replications. in this study, main factor was two levels of irrigation regimes: after 60 (optimum irrigation) and 120 mm (stress) evaporation from evaporation pan class a and subplot were considered combination of zinc foliar application (zero and 1 l/ha, in two levels) and salicylic acid (0, 0.5 and 1 mm). all statistical analyses were carried out using sas software and the correlation was done using mstat-c program. results and discussion in the experiment, the traits were affected by the treatments. water stress significantly decreased grain yield, the number of grains per m2 and oil percent and grain yield. higher number of grain per m2 was at 0.5 mm (2642.2), while stress reduced the number of grains. other studies reported similar results in agreement with this character (banks, 2004). there were significant changes between the irrigation treatments in grain yield. although the application of zn and sa in all irrigation levels had desirable effects on grain yield, significant changes not observed in their interactions. however, these effects were significant at simple affects, the interaction irrigation in zn and salicylic acid maximum amounts of grain yield were produced under stress conditions in plots that containing of zn and 1 mm sa. increased concentration of salicylic acid and stress has decreased the oil content (2/4 and 4.7%, respectively), while the protein (9.1%) was increased. foliar application of zinc and 0.5 mm salicylic acid increased grain oil (26.23 percent) and protein (39.99 percent) content. triple interactions had a significant effect on grain protein and oil content. in the present study, water stress had significant effect on grain oil content and decreased it by 4%. zahedi et al (2009) reported that oil percent was decreased by drought stress, most likely because of a reduction by photosynthesis and assimilate remobilization. trials have shown that unfavorable conditions, especially drought, might alter the grain composition and related qualities (ayad et al., 2010). plants in complete irrigation gave a significantly higher oil yield (540/3 kg/ha). according to the correlation coefficients, oil yield is directly link with grain yield (r= 0.7**) and oil content (r= 0.75**). zn and sa spraying had significant increase and positive effects on protein yield trait, as compared to non-application (table 6). there were no significant interaction effects between irrigation with zn and sa application. irrigation did not significantly affect grain protein yield (table3). conclusions the results showed that water stress significantly decreased yield and grain quality. grain yield, oil and protein yield were increased by using salicylic acid and zinc under stress conditions. the increase of salicylic acid concentration decreased oil and protein content. there was a strong correlation between grain yield and oil and protein yield. in general, the use of zinc and salicylic acid compensated yield reduction due to water stress and it increased grain quality in plant.