Effects of irrigation water qualities and iron sulphate application rates on wheat (Triticum aestivum L.) yield and yield components

Introduction There is an increasing trend in salt affected lands and it plays a crucial role for reduced crop production. Associated with Social and economic dimentions such as employment losses and environmental degradation (Butcher et al., 2016), it is estimated that annual losses of yield due to salt induced land degradation is US$ 27.3 billion globally (Qadir et al., 2014). In addition, it is well documented that application of chemical fertilizers usually improve plant performance under saline conditons but results in plant fertilizer requirement under salt affected soils are contrary. While there is little evidence of yield benefits due to application of fertilizers in salinized fields at rates beyond optimal in non-saline conditions, there is enough evidence indicating that soil salinity does not affect or decrease plant fertilizer needs (Hanson, 2006). These contradictory results can be attributed to the types of experiments (field, greenhouse or laboratory), composition of the saline substrate, studies conducted over the short term vs. the long term and many other differences in experimental conditions (Grattan and Grieve, 1999). The salinity stress may modify the Fe fertilizer management for wheat production under arid and semiarid conditions of Yazd peovince with wide range of irrigation water qualities. Accordingly, the objectives of this field study were to (a) evaluate the interactions between Fe nutrition and the salinity of irrigation water and their effects on wheat growth and (b) test the possibility of wheat improvement at saline conditions by applying higher levels of Fe fertilizer. Materials and methods A field experiment was conducted on wheat at Sadooq Salinity Research Station, Ashkezar, Yazd, Iran. The soil at the experimental site was calcareous with 30.92% total nutrient value, sandy loam texture, pH 8.06 and 0.22 % organic carbon. Mean annual temperatue is 18°C and precipitation is 70 mm. The treatments, four potassium sulphate application rates (0, 100, 200 and 300 kg ha-1) and three irrigation water qualities (1.88, 7.22 , 14.16 dS/m), arranged in a randomized block, split plot design with three repelications. Consisting 12 rows of wheat, each field plot was 3*5 m. All plots received common agricultural practices including tillage and fertilizer application. Rgarding typical recommendations and guidelines for this region and soil type (Balali et al., 2000: Moshiri et al., 2015), all fertilizers, except urea that applied in 4 splits, were soil-applied before plnating and included 100 kg ha-1 triple superphosphate, 40 kg ha-1 ZnSO4, 40 kg ha-1 MnSO4 and 20 kg ha-1 CuSO4. To model the relationship between plant properties and irrigation water salinity, the data were subjected to different regression models at the probability level of 0.01 and 0.05 with the help of the Sigmaplot software. The analysis of variance for different parameters was done following ANOVA technique. When F was significant at p ≤ 0.05 level, treatment means were separated using DMRT. Results and discussion The results showed that increasing irrigation water salinity to 7.22 dS/m did not significantly affect wheat graine yield. This is due to the positive effect of salinity on 1000 seed weight and harvesting index. At the same time, the results showed 50% decrease in wheat grain and straw yield due to the increase in the salinity of irrigation water from 1.88 to 14.16 dS/m. The heighest graine yield for treatments irrigated with irrigation water salinity of 1.88, 7.22 and 14.16 dS/m was obtained from application of 40, 20 and 0 kgha-1 FeSO4, respectively. Overall, it was concluded that salinity stress beyond salt tolerance decreased wheat requirement to iron sulphate fertilizer.