بازچرخانی زهاب مزارع نیشکرجنوب خوزستان برای کشت برنج با هدف بهبود بهره‌وری آب در شبکه‌های آبیاری و زهکشی

تولید زهاب در جنوب استان خوزستان یکی از مشکلات جدی است. استفاده از این زهاب بر میزان تخصیص آب به شبکه‌های آبیاری استان اثرگذاراست. بازچرخانی زهاب برای کشت برنج می‌تواند به‌عنوان بستری مناسب در منطقه مورد توجه قرار گیرد. برای نیل به این هدف، پژوهشی به‌صورت کرت‌های یک‌بار خرد شده در قالب طرح بلوک‌های کامل تصادفی با دو عامل و سه تکرار درکشت و صنعت میرزا کوچک‌خان اجرا شد. دور آبیاری با زهاب نیشکر شامل هرروزه (i0) و تناوب‌ های یک روز در میان (i1) و دو روز در میان (i2) به‌عنوان عامل اصلی در نظر گرفته و 9 رقم و لاین اصلاحی برنج مقاوم به شوری در کرت‌های فرعی قرار داده شدند. نتایج تحقیق نشان داد با کاهش قابل‌توجه آب از دور آبیاری هرروزه به تناوب های یک روز در میان و دو روز در میان، میزان عملکرد ازi0 با متوسط 2140 به 2248 کیلوگرم بر هکتار بهi1 روندی افزایشی دارد و ‌در i2 نسبت به i0 با افتی30 درصد به‌شدت روبه‌رو می شود. در پایش درصد سدیم قابل‌تبادل خاک (esp)، نتایج بررسی ها نشان داد که در هر دو رژیم آبیاری i0 وi1، خاک مزرعه در وضعیت سدیمی بودن قرار نمی گیرد و تنها در وضعیت شور باقی می ماند. این مسئله به‌دلیل آبیاری در سراسر فصل رشد و وجود زهکشی زیرزمینی است که باعث خروج املاح از پروفیل خاک شده است. هرچند در i2، به‌دلیل خشکی دادن مزرعه و هجوم شوری به لایه های سطحی خاک، وضعیت پروفیل خاک تا زیر عمق توسعه ریشه با افزایش 17 درصددر  esp به وضعیت سدیمی نزدیک می شود. معلوم شد در این مدت، شوری عصارۀ اشباع خاک 100 درصد افزایش‌یافته است.

Reuse of Sugarcane Drainage Water for Rice Cultivation in South Khuzestan to Improve Water Productivity in Irrigation and Drainage Networks

Introduction In Khuzestan province, waste water release from various sources, especially from agricultural farms, is a serious problem. The volume of drainage water resulting from irrigation and drainage networks of the Karun river basin is about two billion cubic meters per year, considering sugarcane agroindustries and fish farming as the main sources of drainage water. TimeAveraged salinity of this drainage water, with source of sugarcane agroindustries, is about 6 dS/m which is valuable to irrigate salttolerant crops or aquaculture with saline water as part of the solutions for drainage water management and providing sustainable environment. This can also affect the amount of water allocated to irrigation networks and sugar cane industries. In this regard, reusing of agricultural drainage water to produce rice salinity resistant varieties and lines as a highyielding strategy in Khuzestan, especially in the central and southern areas with high water demand, can be very useful.   Methodology This study was conducted at farm code L0820, in Mirza KoochakKhan AgroIndustry Company, using split plot in a randomized complete block design with two factors and three replications. Irrigation interval with saline water daily, oneday and twoday alternations were main factors and three salinitytolerant rice lines were sub factors. Subsequent selections from the International Treasury of rice cultivars, four salinitytolerant breeding lines, one international control line and local cultivar were subplots. The amount of water applied to the plots was measured throughout the growing season and samples for determination of physical and chemical properties of soil and drainage water before planting until harvesting time for soil monitoring and soil salt balance analysis were collected. In this study, grain yield, biomass and harvest index were determined. Finally, water productivity was estimated as yield per cubic meter of water.   Results and Discussion Due to the average salinity of irrigation water, 6 dS/m, the volume of water consumed during the growing season was estimated to be 30,000 m3/ha, based on water requirement calculations. Based on irrigation management, applied volume of water was estimated about 37500 m3/ha for treatment I0, 19500 m3/ha for treatment I1 and 13200 m3/ha for treatment I3. The average salinity of soil saturated extract was measured about 4 dS/m before cultivation. Except for the first 15 days, when irrigation was carried out with full irrigation for transplanting stage, the trend of soil salinity changes was decreasing, during the rest of the growing season until harvesting. Salinity of soil increased in all three irrigation managements. The rate of salinity changes varied from 50% in the daily irrigation round to 100% in the twoday irrigation round, compared to precultivation soil salinity. During the crop growth from the transplanting, daily, oneday and twoday rounds irrigation managements caused enterance of 190, 99 and 66 tonnes of salt in the top 100 cm of soil profile. Increased salinity over growing time for daily, oneday and twoday round irrigation treatments, were 6, 6.5 and 7.2 dS/m respectively, according to soil salinity, 4 dS/m, before planting. Assuming the  porosity of soil equal to 51%, it could be concluded that 7.6, 9 and 11 tonnes of salts stored in the upper 60 cm of soil profile for daily, oneday and two day round irrigation management and the rest of the solutes extracted from soil profiles through underground drainage system. This behavior illustrated the importance of drainage, especially underground drainage system, in agricultural drainage reclamation and saline operations for soil conservation. The results showed significant decrease of farm applied water in daily irrigation water management relative to twoday and threeday intervals. Farm yield increased 6% from I0 with an average of 2139.3 to 2248 kg, I1 and then decreased by 30% in the threeday irrigation period.   Conclusions The results showed that the highest and lowest water productivity were found in I2 and I0 irrigation treatments, respectively, with values of 0.128 and 0.057kg/m3. ESP monitoring showed that at the end of growing season, soil profile was not sodic and remained in saline condition for two irrigation regimes I0 and I1. However, in I2 irrigation regime, the soil profile status approached to the sodic state, with 17% increasing in ESP and 100% increasing in salinity relative to planting time. The reason for this behavoir was driness of land between two irrigation events which caused salinity moving upward to soil surface layers, so it could be addressed by considering the percentage of leaching at the end of the growing season.   Acknowledgement  The authors gratitude Mirza KoochakKhan AgroIndustry Company, Khuzestan Water and Power Authority (KWPA), Agricultural Engineering Research Institute (AERI), Rice Research Institute of Iran )RRII), Khuzestan Agricultural and Natural Resources Research and Education Center  for their  overall supports to accomplish the study.