تغییرات شوری و سدیمی شدن خاک در شرایط آبیاری قطره‌ای زیرسطحی و آبیاری جویچه‌ای نیشکر

یکی از چالش های آبیاری قطره ای زیرسطحی در مناطق خشک و نیمه خشک، تجمع املاح در لایۀ سطحی خاک است. این پژوهش به منظور بررسی تغییرات شوری و سدیمی شدن خاک در دو مزرعۀ آزمایشی آبیاری قطره ای زیرسطحی و آبیاری جویچه ای واقع در کشت و صنعت حکیم فارابی خوزستان به اجرا درآمد. در این تحقیق، تغییرات شوری خاک در عمق های 30-0، 60-30 و 90-60 سانتی متری و تغییرات نسبت جذب سدیم (sar) در لایۀ سطحی (30-0 سانتی متری) خاک در دورۀ رشد نیشکر (دو (t1)، چهار (t2)، شش (t3)، هشت (t4)، ده (t5) و دوازده (t6) ماه پس از شروع آبیاری) بررسی شد. نتایج تحقیق نشان داد هدایت الکتریکی (ec) خاک در عمق های 30-0 و 60-30 سانتی متری، در همۀ زمان های مورد بررسی به جز t1 و t5 (آبیاری سطحی در مزرعه قطره ای زیرسطحی)، به طور معنی داری تحت تاثیر روش آبیاری قرار می گیرد. بیشترین اختلاف بین مقدار ec خاک در مزرعۀ آبیاری قطره‌ای زیرسطحی با مزرعۀ آبیاری جویچه‌ای، مربوط به زمان‌های نمونه‌برداری t3 و t4 بوده است که در این زمان ها میانگین ec خاک در مزرعه آبیاری قطره‌ای زیرسطحی در عمق 30-0 سانتی متری به‌ترتیب 2/47 و 1/98 برابر میانگین ec خاک مزرعه آبیاری جویچه‌ای بوده است. غلظت سدیم انحلال پذیر و مقدار sar خاک در عمق 30-0 سانتی متری خاک، در همۀ زمان‌ها به جز t5، در مزرعۀ آبیاری قطره‌ای زیرسطحی، به طور معنی داری بیشتر از مزرعه آبیاری جویچه‌ای و در زمان t5، به طور معنی داری کمتر از آبیاری جویچه‌ای بود. در زمان نمونه برداری t5، آبیاری سطحی در مزرعۀ آبیاری قطره ای زیر سطحی، سبب آبشویی املاح لایه سطحی خاک و کاهش sar خاک شد. بیشترین مقدار sar خاک (1/13) در مزرعه آبیاری قطره ای زیرسطحی مربوط به زمان نمونه‌برداری t4 بود. بنابراین، در کنار استفاده از سیستم آبیاری قطره ای زیرسطحی در شرایط مناطق خشک و نیمه خشک خوزستان، نیاز است امکان آبیاری به روش سطحی نیز به منظور مدیریت شوری خاک فراهم گردد.

changes in soil salinity and sodicity under subsurface drip irrigation and furrow irrigation of sugarcane

extended abstractaccumulation of solutes in the surface layer of soil is one of the challenges of subsurface drip irrigation, especially in arid and semi-arid regions. this study was carried out in order to investigate soil salinity and sodicity in two experimental fields of subsurface drip irrigation (with a drip irrigation depth of 20 cm) and furrow irrigation located in the khuzestan hakim-farabi agro-industry. in this study, the changes in soil salinity at the depths of 0-30, 30-60, and 60-90 cm  and sodium absorption ratio (sar) in the surface layer (0-30 cm) were investigated during the growth period of sugarcane (2 (t1), 4 (t2), 6 (t3), 8 (t4), 10 (t5) and 12 (t6) months after the start of irrigation). the average data were compared using the t-test at the 5% probability level. the results indicated that the soil electrical conductivity (ec) at both the depths of 0-30 and 30-60 cm, in all the times, except for 2 (t1) and 10 (t5) months after the start of irrigation (surface irrigation + subsurface drip field), was significantly affected by the irrigation method. the highest difference between the soil ec in the subsurface drip irrigation field and the furrow irrigation field was recorded at the t3 and t4 sampling times. in these sampling times the average soil ec in the subsurface drip irrigation field at a depth of 0-30 cm was 1.47 and 1.98 times greater than that of furrow irrigation field. in all the sampling times, except for t5, the soil sar at depth of the 0-30 cm, in the subsurface drip irrigation field, was significantly higher than that in the furrow irrigation field; and in the t5 sampling time, it was significantly lower than that in the farrow irrigation. at the t5 sampling time, surface irrigation in the sub-surface drip irrigation field led to leaching of accumulated salts in the surface layer of the soil and reduced the soil sar. the highest of soil sar (13.1) value in subsurface drip irrigation field was related to t4 sampling time. therefore, it seems that besides using a subsurface drip irrigation system in arid and semi-arid regions, it is necessary to provide the possibility of surface irrigation in order to manage soil salinity and sodicity.introduction in arid and semi-arid regions, optimal use of water resources and management of soil resources is necessary to achieve sustainable agriculture. accumulation of solutes in the surface layer of the soil is one of the challenges of subsurface drip irrigation, especially in arid and semi-arid regions. in the drip irrigation system, the distribution and accumulation of soluble soil salts in the surface layer of the soil is more than that in the deeper layers and it increases with increasing distance from the drippers. soil salinity in the subsurface drip irrigation method should not be ignored, because in this irrigation method, even in good water quality conditions, some amount of water is transferred to the soil and the salt concentration on the soil surface gradually increases. therefore, it is necessary to monitor and control the soil salinity in subsurface drip irrigation conditions. this study was carried out in order to investigate the soil salinity and sodicity status under subsurface drip irrigation and furrow irrigation during sugarcane growth period.methodologythis study was carried out in two experimental fields of subsurface drip irrigation (with a drip irrigation depth of 20 cm) and furrow irrigation located in the khuzestan hakim-farabi agro-industry. in this study, the changes in soil salinity at the depths of 0-30, 30-60, and 60-90 cm  and sodium absorption ratio (sar) in the surface layer (0-30 cm) were investigated during the growth period of sugarcane (2 (t1), 4 (t2), 6 (t3), 8 (t4), 10 (t5) and 12 (t6) months after the start of irrigation). the average data were compared using the t-test at the 5% probability level.results and discussionthe results showed that at all sampling times, electrical conductivity (ec), concentration of soluble cations (na, ca and mg) and sar of the soil in the subsurface drip irrigation field were more than the furrow irrigation field. the results indicated that the soil electrical conductivity (ec) at both the depths of 0-30 and 30-60 cm, in all investigated times except 2 and 10 months after the start of irrigation (surface irrigation in subsurface drip field), was significantly affected by the irrigation method. the results of this research showed that in all sampling times of salinity, the concentration of soluble cations (na, ca and mg) and sar of the soil in the subsurface drip irrigation field was higher than that in the furrow irrigation field. the greatest difference in the soluble concentration of na, ca and mg in the soil in the two studied fields was related to the t4 (8 months after cultivation). at this sampling time, the average soil soluble concentration of na, ca and mg in the subsurface drip irrigation field was 2.1, 1.95 and 1.93 times their values in the furrow irrigation field, respectively. in all sampling times except t5, the soil sar at the 0-30 cm depth, in the subsurface drip irrigation field, was significantly higher than in the furrow irrigation field, and in t5 sampling time, it was significantly lower than farrow irrigation. at the t5 sampling time, surface irrigation in the sub-surface drip irrigation field led to leaching of accumulated salts especially na in the surface layer of the soil and reduced the soil sar.         conclusionsaccording to the results of this study, it seems that besides using a subsurface drip irrigation systems in arid and semi-arid regions (like khuzestan province), it is necessary to provide the possibility of surface irrigation in order to manage soil salinity and sodicity. moreover, considering that sugarcane is a perennial plant, it is necessary to pay attention to soil solute leaching in order to control salinity in the management of sugarcane fields.acknowledgementthe authors of the article thank and appreciate the khuzestan sugarcane research and training institute for their financial support and assistance in the various stages of this research.