Effect of Vermicompost on Tomato Salt Tolerance and Availability of Iron and Zinc in a Calcareous Soil

Salinity stress and micronutrient deficiency are the most important factors limiting crop production in the calcareous soils in central area of Iran. One of the sustainable strategies to maintain the productivity and improve the fertility status of soil, particularly in arid and semi-arid regions with a soil having low input of organic material, is the use of organic and biological fertilizers with chemical types. In this study, the effect of different vermicompost levels including 0, 10 and 20 % (the weight ratio of vermicompost to the soil) on the nutrient uptake, growth and yield of tomato was investigated at three salinity levels, i.e. 0, 40 and 80 mM NaCl (electrical conductivity of 0, 3.65 and 7.30). The results showed that the salt stress caused significant reduction in root and shoot yield, but these negative effects of salt stress were significantly reduced by vermicompost application. The positive effect of the vermicompost on the plant growth was depended on the applied vermicompost levels. Salinity significantly increased the shoot Na concentration (375 %) and decreased the K concentration (23 %). The shoot Fe and Zn concentrations were also decreased by salinity from 338 and 31 mg kg-1 to 307 and 25 mg kg-1, respectively, while application of the vermicompost caused significant increase of these nutrients concentration in tomato. The effect of vermicompost on K:Na ratio was not significant while the salt stress caused significant reduction in this ratio. Based on these results, in addition to maintaining the nutrients balance in saline conditions, vermicompost could increase concentrations of Fe and Zn in plant and thereby reduced the stress-induced oxidative damage.