Document Type : Research Paper

Authors

• M. Khorramian
• S. Salimpour

Abstract

IntroductionThe area cultivated for wheat is about 550000 ha in Khuzestan province. Limited rainfall conditions and incompatibility of rainfall patterns with wheat crop requirements leads to decreasing of soil moisture and drought stress. Studies have shown that water supply affects the uptake of nutrients and nutrient use effeciency. On the other hand, the benefical effect of the application of zinc and potash nutrients under different water stress in Khouzestan is not convenient for farmers. Therefore, this study aimed to determine the effect of drought stress and zinc and potash in silty clay loam soil on yield and water use efficiency (WUE) of wheat.
Materials and Methods The experiment was carried out in Safiabad Agricultural Research Center (SARC) of Dezful, Khuzestan during the years of 2008-09 and 2009-10. Before the experiment, initial composite soil samples (0-30 cm & 30-60cm depth) were collected from the experimental plots and were analyzed. The soil was silty clay loam with low organic matter content (OC=0.5-0.75%) and well drained without salinity (ECe=0.27-1.3 ds m^-1). On the other hand, micronutrient content of the soil (Fe, Mn and Cu) was higher than the threshold limit. The design was a split plot on a completely randomized block design with three replications. The main plot consisted of three different levels irrigation after 50 (I₅₀), 75 (I₇₅), and 100 mm (I₁₀₀) evaporation from evaporation pan and sub plots included three levels of fertilizers, without micronutrient (F₀), fertilizing based on soil analysis value (F₁), and fertilizing basesd on 1.5 times more than the recommended level (F₂). Every subplot size was 3.6 m x 10m. The studied cultivar was Chamran and the sowing date was on November with a density of 400 seeds per m^-2 and harvested during May in both growing seasons. Soil moisture content was measured before every irrigation in root zone depth using the weighning method. Applied water was measured using flow meter for every treatment. After seed ripening, grain yield per hectare and component yield were measured from the total area of each treatment. Statistical analysis was performed using MSTATC software packages and mean comparison was also performed using Duncan’s Multiple Range Test (DMRT).
Results and Discussion The rainfall during plant growth for first and second years was 68 and 221 mm respectively. The mean temperature of Mars and April in the seconed year was 26.1 and 34^°C increasing by about 1.4 and 1.9^°C compared to the first year. The higher temperature in the second year increased heat stress which led to yield decrease. Irrigation water consumptions in first year for I₅₀, I₇₅, and I₁₀₀ treatment were 960.6, 804.1 and 682.2 mm and in the second year 182,115 and 95 mm respectively. Higher rainfall in the second year in comparison with the first year led to decrease in number of irrigation events. All the studied parameters except for 1000-grains weight and number of grains per spike were significantly influenced by different levels of fertilizer treatments.The highest yield belonged to fertilizing based on soil test results (F₁), (40 kg K per ha, Zinc Sulfat with 200 kg per ha potash) while the lowest yield was found in the control treatment(F₀). Cakmak et al. (1996) and Yilmaz et al.(1997) also observed similar responses. A similar trend was observed in the biological yield,  number of spike and 1000-grains weight. Increasing rates of K and zinc(up to 40 kg.ha^-1) increased the values of crop parameters such as biological yield,  number of spike , 1000-grains weight and water use efficiency and thereafter higher levels of K and zinc fertilizer (F2 treatment) led to their decline. Analysis of variance on yield showed that irrigation regime, potash and zinc fertilizer levels were significantly different (p<5%), so that the highest and the lowest yield belonged to I₅₀F₂ with 673.5 gr m^-2 and I₁₀₀F₀ with 450.3 gr m^-2 respectively. Although there was no significant difference between F₁ and F₂ treatments, increasing the applied fertilizer in I₅₀ treatment increased yield and water use efficiency. On the other hand, applying potash and zinc fertilizer more than recommended levels in soil under moisture stress (I₇₅ and I₁₀₀), resulted in decreased yield.
Conclusion The overall results from this study indicated that it is essential to avoid applying potash and zinc fertilizers over recommended values in soil under moisture stress conditions. Intraction between different irrigation levels in combination with fertilizer showed that I₇₅F₁ with yield and WUE, of 6.4 t ha^-1 and 1.28 kg m^-3 respectively could be recommended.

Keywords

• Drought stress
• Wheat nutrition
• Khuzestan