Physiologic and agronomic response of wheat to application of zinc in irrigation with saline water

Shortage of non-saline and high quality irrigation water is a serious problem in agricultural farms which limits crop productions. Proper nutrient management is one of the key solutions to decreasing the adverse effects of salinity. Zinc is an essential trace element that can alleviate the negative effects of toxic ions on plant growth under the saline environments. Therefore, in this study, the effect of zinc an enhancer agent of saline irrigation water of wheat farms was investigated.

A factorial experiment was conducted based on randomized completed block design with four replications. The Experiment was under the greenhouse condition located in Borazjan Research Institute of Agriculture and Natural Resources during 2012-2013. The first factor comprised four levels of salinity including 4 (control), 8, 12 and 16 dS.m-1. The second factor was application of four levels of zinc including 0, 10, 20 and 30 mg.kg-1 soil.

Our results suggested that increase in zinc concentration could significantly alleviate negative effects of salinity stress on plant height. The highest plant height (84.13 Cm) was achieved by application of 30 mg.kg-1 soilzinc. Although increase in salinity stress reduced wheat growth potential there was no significant difference between 4 dS.m-1 (86.32 Cm) and 8 dS.m-1 (80.19 Cm) on the plant height. The lowest number of grain in spike (36.19) was observed in control treatment while the maximum number of grain in spike (53.44) was produced under 30 mg.kg-1 soil zinc. Increase of salinity from 4 to 16 dS.m-1 drastically reduced the number of grain in spike from 50 to 39.69. Application of 30 mg.kg-1 soilzinc resulted in higher RWC (85.02%) compared to control (69.30%). Increase in zinc concentrations led to a higher chlorophyll and carotenoid content. There was no significant difference between 10 and 20 mg.kg-1 soilzinc sulfate on chlorophyll content. Increasing salinity from 4 dS.m-1 to 12 dS.m-1 resulted in reduction of chlorophyll a from 2.58 to 2.08 mg.gr-1 fw, chlorophyll b from 0.79 to 0.59 mg.gr-1 fw and total chlorophyll from 3.76 to 2.90 mg.gr-1 fw. Zinc promoted synthesis of carotenoid. Carotenoid contents reached 8.43 mg.gr-1 fw by the application of 30 mg.kg soil-1. The maximum carotenoid content (9.30 mg.gr-1 fw) was observed at 8 dS.m-1 salinity while there was no significant difference with carotenoid content of 4 dS.m-1 (8.99 mg.gr-1 fw). However, by increasing salinity stress, the carotenoid content significantly reduced and the lowest carotenoid content (6.70 mg.gr-1 fw) was observed at 16 dS.m-1 salinity. Zinc content of leaf and grain of wheat significantly increase by the application of 30 mg.kg-1 soil zinc and in the highest concentration of fertilizer, zinc content of leaf and grain reached 32.07 and 63.76 mg.kgr-1 respectively. The highest wheat biological yield (1577.50 g.m-2) was observed in 4 dS.m-1 with 30 mg Zn kg-1 soil while the lowest biological yield (986.39 g.m-2) was observed at no added fertilizer and salinity of 16 dS.m-1. The maximum wheat grain yield (692.03 g.m-2) was observed in salinity of 4 dS.m-1 with 30 mg Zn kg-1 soil while the lowest grain yield (459.39 g.m-2) was observed at no added fertilizer treatment and salinity of 16 dS.m-1. Our results clearly proved that application of zinc could alleviate negative effects of salinity stress on wheat grain yield. Wheat biological yield at salinity of 16 dS.m-1 with no added fertilizer reached 986.39 g.m-2 while at the same salinity, application of 30 mg Zn kg-1 soil zinc enhanced biological yield to 1131.80 g.m-2. Although salinity level from 4 to 16 dS.m-1 significantly reduced wheat grain yield application of 30 mg.kg-1 soil zinc increase grain yield from 459.39 g.m-2 to 506.94 g.m-2 in 16 dS.m-1 salinity.

Wheat yield was significantly affected by the quality of irrigation water. The higher the concentrations of salinity, the lower wheat yield will be produced. However, our results revealed that application of zinc is an effective way of reducing salinity to restrict wheat grain yield. This trace element enhances plant production of photosynthetic pigments; therefore, physiological performance of the crop was improved under saline conditions. Application of 30 mg Zn kg-1 soil was highly recommended in farms with saline irrigation water