Wheat yield and physico-chemical properties of a sodic soil from semi-arid area of Iran as affected by applied gypsum

Irrigation by highly sodic water has been practiced only in recent years in Iran but has led to impaired productivity of thousands of hectares of agricultural lands. So, the present study was set out to evaluate the effectiveness of different rates and sizes of gypsum as an amendment which improves the physical and chemical properties of soil and crop productivity. A field experiment was conducted in a sodic soil at a farmer's field in Ramjerd, Fars. The treatments consisted of two gypsum granule sizes (1–10 mm and < 1 mm), and two application methods (adding gypsum to the irrigation water and mixing it with soil) were employed at three soil-applied gypsum levels, i.e., 50%, 75% and 100% of gypsum requirement (GR). The findings of the study showed that the application of gypsum increased soil salinity and hydraulic conductivity but decreased sodium adsorption ratio (SAR) and pH. The increase of wheat yield in coarse gypsum was greater than that observed in fine gypsum but, concerning most soil and plant parameters, the difference between fine and coarse gypsum was not significant at all in terms of rates of GR. Drought condition was found to diminish the effect of gypsum on soil and plants as a 10% reduction in wheat yield was observed in a drought year as compared with a normal year. Plant density, fertile spikelets, and 1000-grain weight were improved as the soil-applied gypsum increased. Regarding chemical composition of leaf, plants grown on un-amended plots had higher Na and lower potassium (K) and calcium (Ca) concentrations in leaf tissue. The application of gypsum caused a significant increase in nitrogen (N), phosphorus (P), Ca, K, iron (Fe), and zinc (Zn) concentrations in wheat tissue but copper (Cu) and manganese (Mn) concentrations remained unchanged. It also increased Ca:Na and K:Na ratios in leaf tissue and had positive effects on crop yield. It was finally recommended that farmers reclaim sodic soil by applying coarse gypsum at the rate of 100% GR since it is a more cost-effective way of reclamation of sodic soil.