بررسي حساسيت درون فصلي تبخير-تعرق ذرت به تنش آبي، در سطوح مختلف آبياري

Investigation of the Intra-Seasonal Sensitivity of Maize Evapotranspiration to Water Stress, at Different Irrigation Levels

در اين پژوهش حساسيت تبخير-تعرق ذرت به تنش آبي، در مراحل متمايز رشد و براي شرايط كاربرد مقادير مختلف آب آبياري بررسي شد. آزمايش به‌صورت فاكتوريل و در قالب طرح بلوك‌هاي كامل تصادفي انجام شد. تيمارهاي آبياري شامل چهار سطح (I0)100، (I1)80، (I2)60 و (I3)40 درصد نياز آبي گياه و تيمارهاي مراحل رشد شامل چهار مرحله‌ي اوليه، توسعه، مياني و پاياني رشد بود. تبخير-تعرق روزانه گياه بر اساس بيلان آب خاك در منطقه ريشه اندازه‌گيري شد. مقادير تبخير-تعرق در مراحل رشد مذكور به‌ترتيب برابر با 79، 201/8، 123/8 و 14/6 ميلي‌متر (در تيمار I0)، 78/3، 196، 112/6 و 14/6 ميلي‌متر (در تيمار I1)، 72، 173/6، 99 و 11/7 ميلي‌متر (در تيمار I2)، 62/8، 147/5، 81/5 و 8/4 ميلي‌متر (در تيمار I3) اندازه‌گيري شد. مقدار عملكرد خشك ذرت در تيمارهاي I0، I1، I2 و I3 به‌ترتيب برابر با 1/17، 8/15، 6/12 و 7/8 تن بر هكتار بود. در كل دوره رشد و در سطوح آبياري I1، I2 و I3، مقدار تبخير-تعرق نسبي ذرت به‌ترتيب 95/6، 85 و 71/6 درصد و مقدار عملكرد نسبي محصول به‌ترتيب 4/92، 7/73 و 9/50 درصد برآورد شد. در اين پژوهش ضرايب حساسيت درون فصلي تبخير-تعرق ذرت به تنش آبي، از طريق مدل جنسن مدل‌سازي شد. به‌اين صورت كه براي داده‌هاي واقعي هر تيمار تحت تنش (I1الي I3) و در مراحل اوليه، توسعه، مياني و پاياني رشد ذرت، به‌ترتيب ضرايب حساسيت الي (موجود در مدل جنسن) توسط نرم‌افزار SPSS برآورد شد. ميانگين ضرايب مذكور در تيمارهاي تحت تنش به‌ترتيب برابر با 0/421، 1/37، 0/274 و 0/133 تعيين شد. براي صحت‌سنجي مدل جنسن در تخمين عملكرد نسبي واقعي ذرت، از آماره‌هاي ارزيابي ، EF، RMSE، ME و CRM استفاده شد. آماره‌هاي مذكور به‌ترتيب برابر با 0/998 0/986 2/753، 0/026 و 0/021 محاسبه شد كه نشان‌دهنده كارايي خوب مدل در تخمين عملكرد نسبي محصول بود. همچنين در سطوح مختلف آبياري، بين دو پارامتر تبخير-تعرق و عملكرد زيست‌توده خشك ذرت، رابطه‌ي Y=69.935ET-12281 با ضريب همبستگي 0/999 برازش داده شد. انتخاب مرحله‌ي رشد مناسب به‌منظور اعمال تنش آبي و سطح تنش وارده، تاثير به‌سزايي در مقدار تبخير-تعرق و توليد زيست‌توده گياهي داشت. دستاورد كاربردي پژوهش اين بود كه با استفاده از مدل‌ها و روابط بين تبخير-تعرق و عملكرد گياه، مي‌توان بر اساس مقدار تبخير-تعرق واقعي و تحت مديريت در مراحل مختلف رشد، مقدار عملكرد واقعي محصول را تخمين زد. همچنين با توجه به تاثير شدت تنش آبي بر كاهش تعرق گياه و افزايش تبخير از سطح خاك، استفاده از مالچ روي خاك به‌خصوص در مراحل اوليه و پاياني رشد قابل توصيه بود.

ntroduction: Adeqiate water use in the agricultural sector requires accurate knowledge of crop sensitivity to environmental stresses (such as water stress). The crop sensitivity to water stress may be different at different growth stages and may have a different effect on the actual amount of crop evapotranspiration compared to the standard conditions. At different levels of water stress, studying the sensitivity of crop evapotranspiration at different growth stages can be provided management strategies for optimal water consumption. In the present research, the intra-seasonal sensitivity coefficients of maize were modeled by using the Jensen model. Materials and Methods: In this research, the effect of water stress levels and growth stage sensitivity on the amount of maize (S.C 704) evapotranspiration was investigated. The experiment was performed as factorial based on randomized complete block design. The treatments included four irrigation levels of 100 (I0), 80 (I1), 60 (I2), and 40 (I3) percent of the crop water requirement and four growth stages of initial, development, middle and final. In between two irrigations, the amount of daily soil moisture was measured in the center of each plot and the depth of the crop root zone. Therefore, the amount of evapotranspiration of crops per unit area was estimated according to the soil water balance. Analysis of variance and mean data comparison of evapotranspiration and dry biomass yield were performed by SPSS software and using Duncan's multiple tests. By actual evapotranspiration and yield data, intra-seasonal sensitivity coefficients of maize to water stress (λ1 to λ4) were determined by SPSS software. Results and Discussion: Evapotranspiration The effect of irrigation water amount and growth stage on the maize evapotranspiration amount was significant at the probability level of 1%. Evapotranspiration amounts at the initial, developmental, middle, and final of maize growth stages were estimated equal to 79, 201.8, 123.8 and 14.6 mm (in I0 treatment), 78.3, 196, 126.6 and 14.6 mm (in I1 treatment), 72, 173.6, 99 and 11.7 mm (in I2 treatment), 62.8, 147.5, 81.5 and 8.4 mm (in I3 treatment), respectively. Reduction of evapotranspiration compared to control treatment (I0) in the initial, developmental, middle, and final growth stages were estimated equal to 0.9, 2.8, 9, and 0 (in I1 treatment), 8.8, 14, 20, and 19.8 (in I2 treatment), 20.5, 26.9, 34.2 and 42.4 (in I3 treatment) percent, respectively. The results showed that the slope of evapotranspiration reduction was not the same at different irrigation levels. Also, the relative evapotranspiration of maize (in all growth seasons) at irrigation levels of I1, I2, and I3 were estimated equal to 95.6, 85, and 71.6 percent, respectively. Therefore, when applying water stress, the optimal evapotranspiration rate can be adjusted by selecting the suitable growth stage. Yield The effect of irrigation levels on the dry biomass yield of maize was significant at the level of 1% probability. The dry yield of maize in treatments of I0, I1, I2, and I3 were equal to 17.1, 15.8, 12.6, and 8.7 (tons per hectare), respectively. The relative yield of maize at irrigation levels of I1, I2, and I3 were estimated to be 92.4, 73.7, and 50.9 percent, respectively, in the Qazvin region. The reduction of soil available water affected the water uptake by the crop and reduced the yield of maize. Modeling of intra-seasonal sensitivity coefficients of water stress At the initial, developmental, middle, and final growth stages of maize, stress sensitivity coefficients of λ1, λ2, λ3, and λ4 were estimated in water stress treatments. The mean of mentioned coefficients in stress treatments was calculated to be 0.421, 1.37, 0.274, and 0.133, respectively. The results showed that during the development stage of maize growth, the effect of water stress on yield reduction was more. The model efficiency for estimating the amount of relative yield was evaluated. Evaluation statistics of R2, EF, RMSE, ME and CRM were estimated to be 0.998, 0.986, 2.753, 0.026 and 0.021, respectively. The results showed that the Jensen model efficiency was good, and it can be used in planning the low irrigation for different growth stages of maize. Yield-Evapotranspiration Function of Maize in all of the growth stages Across different irrigation levels, a simple linear relationship of Y=69.935ET-12281 (with a correlation coefficient of 0.999) was fitted between two parameters of evapotranspiration and dry biomass yield of maize. Therefore, using the above equation in low irrigation management, the amount of maize yield can be estimated based on the evapotranspiration amount. In this research, 175 mm evapotranspiration was needed for the production of the initial unit of maize biomass. That is, the transpiration portion in the above amount was negligible, and it was mostly allocated to the soil evaporation portion. Conclusion: The crop sensitivity to water stress and different needs to transpiration at different growth stages were the reasons for the different reduction of maize evapotranspiration. Reduction of soil available water reduced the water uptake and transpiration, and crop biomass. The results showed that reducing the water stress was effective in increase of maize evapotranspiration efficiency. In order to produce the maximum crop biomass, the sensitivity of the maize growth stage and the water stress level must be considered