Elucidation of wheat response to phosphorous application rates and salinity stress under field conditions

Introduction Salinity stress is known as a worldwide plant growth limiting factors (Alavimatin et al., 2015: Atlasipak 2018). In addition, it is estimated that around 50 percent of arable lands are affected by salinity stress by 2050 (Butcher et al., 2016: Qadir et al., 2014). The use of chemical fertilizers is a common practice in arid soils for improving plant performance grown under non-fertile soils. While there is little evidence of yield benefits due to application of fertilizers in salt affected soils at rates beyond optimal in non-saline conditions, there is enough evidence indicating that soil salinity does not affect or decrease plant fertilizer requirements (Hanson, 2006). Accordingly, the objectives of this field study were to (a) evaluate the interactions between phosphorous 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 phosphorous 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 triple superphosphate 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 with three replications. 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 planting and included 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 LSD. Results and discussion The results showed that increasing irrigation water salinity to 7.22 dS/m did not significantly affect wheat grain 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. Conclusion Overall, it was concluded that application of triple superphosphate at a rate of 150 kgha-1 is recommended for wheat yield improvement at irrigation water salinity of 1.88 and 7.22 dS/m. As wheat performance irrigated with irrigation water salinity of 16.14 ds/m was not affected by different rates of phosphorous fertilizer, it can be concluded that wheat phosphorous requirement decreased at irrigation water salinity beyond salt tolerance. Key words: Irrigation water, Salinity and Triple superphosphate.