اثر رژیم‌های آبیاری بر توزیع رطوبت و شوری اطراف ریشه ذرت در شرایط آبیاری قطره‎ای

در پژوهش حاضر به‌منظور بررسی کارایی آبیاری قطره­ای نواری و همچنین تاثیر این سامانه آبیاری بر شوری خاک، در خاک‌های ریزبافت مستعد به شوری و سدیمی استان خوزستان، اقدام به کشت گیاه ذرت تابستانه گردید. آبیاری قطره­ای نواری با سه دور آبیاری دو، سه و چهارروزه بر اساس نیاز آبی گیاه تعیین شد و در قالب کرت نواری در بلوک کامل تصادفی اجرا گردید. برای پایش رطوبت و شوری در هر مرحله از رشد گیاه نمونه­ های خاک در لایه­ های 025، 5025، 7550 سانتی­متری در محدوده ریشه گیاه برداشت شد. این نمونه‎گیری­ها در دو سال زراعی انجام شدند تعیین میزان رطوبت خاک به روش وزنی انجام شد. در تیمار 2 روزه لایه رطوبت 0 تا 25 سانتی­متری خاک قبل از آبیاری حدود 16% وزنی بوده و بعد از آبیاری به 18% وزنی و در تیمارهای 3 و 4 روزه به 23% وزنی رسیده است. به‌طورکلی درصد رطوبت در تمام طول فصل زراعی در ناحیه ریشه گیاه در حد ظرفیت مزرعه نگه داشته شد. نتایج حاصل از شوری خاک نشان داد که در سال اول کشت شوری خاک در طی دوران رشد و پس از اتمام فصل کشت روند افزایشی داشته است برخلاف آن پس از سال دوم کشت شوری خاک به یک‌چهارم شوری اولیه رسیده است. این روند در آبیاری سطحی نیز مشاهده شد. حرکت شوری از رژیم آبیاری دوروزه به چهارروزه، روندی افزایشی داشته است. بررسی توزیع شوری در اعماق مختلف ریشه گیاه، بهترین عمق خاک را عمق صفر تا 25 سانتی‎متری در آبیاری دوروزه و با شوری 2.9 دسی ­زیمنس بر متر به نسبت شوری در آبیاری سه و چهارروزه معرفی می­کند. با توجه به بررسی توزیع رطوبت، شوری و عملکرد در هر سه رژیم آبیاری می­توان رژیم آبیاری 2روزه را مناسب‌ترین رژیم آبیاری برای استفاده از آبیاری نواری تیپ در خاک­های سنگین خوزستان معرفی نمود.

Impact evaluation of different irrigation regimes on moisture and salinity distribution around the roots of maize plant under drip irrigations

IntroductionDrip irrigation delivers moisture to the soil surrounding the plant root, leaving the uncultivated ridges mostly dry. The dynamics of dryness and moisture can help adjust the soil salinity and redistribute moisture and salinity (Li et al., 2013; Wang et al., 2011). Further, the distribution of soil salinity in arid regions is affected by a multitude of factors, including the water table (Ming et al., 2016), groundwater salinity, (Abliz et al., 2016), irrigation system (Lie et al.,2013;Zhang et al.,2017), and soil texture (Hu et al., 2011; Zhang et al., 2014). Given the complexity of investigating moisture and salinity distribution in the soil and their uptake by plant roots, the subject has been addressed by several studies around the world. The present study attempts to investigate and evaluate the effects of different irrigation regimes (two, three, and fourday) using a tape drip irrigation system on the diffusion and distribution of salinity and moisture around the root of summer maize over two crop years (2018–19) in the South Khuzestan region, where a heavy soil texture is predominant.Materials and methodsLocated between the 29°57’ N and 33°0’ N relative to the equator, and between 47°40’ E and 50°33’ E relative to the prime meridian, Khuzestan Province occupies 64,057 square kilometers in Southwest Iran. The present study was carried out in a research farm at the Center for Agriculture and Natural Resources Research and Training, Ahwaz, Khuzestan Province, in summers 2018 and 2019. With clay and silty clay soil textures, shallow and saline groundwater (1.5 m depth), and its particular climate, this research farm can be representative of the farmlands of Central and Southern Khuzestan. The required volume of water during each irrigation by the drip tape irrigation system under different irrigation regimes (two, three, and fourday) was calculated for different plant development stages and treatments, thus enabling control over the different irrigation hours in different regimes. the farm soil was sampled at four stages, namely before planting, upon germination, during the middle development stage, and after planting), for physical and chemical characterization and monitoring salt levels from three depths (0–25, 25–50, and 50–75 cm) at a 20 cm distance from the tape by manual excavation using an auger (10 cm in diameter and 20 cm in length). Soil salinity and other quality criteria were measured in the lab. Further, the SMC was measured by the weight percent method, which involves weighing and drying the samples.Results and discussionThe present study addressed moisture and salinity distribution in the soil profile around the plant root under different irrigation regimes. The moisture distribution results showed that all irrigation regimes (two, three, and fourday) could maintain the moisture around the FC, slowing down the vertical flow and minimizing penetration into depths. The soil salinity results showed that, considering the soil salinity conditions at the start of the growing season, using the drip tape irrigation first reduced and then increased salinity in the first year of cropping. In contrast, in the second growing season, soil salinity at the end of the growing season using two, three, and fourday irrigation regimes was cut to a fourth and a third of its initial level. This shift in the behavior was, however, due to the differences in the quality of irrigation water. This outcome shows the susceptibility of using the drip tape irrigation system in soils that are prone to sodicization and salinity, which requires preparing the conditions to ensure the sustainable function of the irrigation system. The final set of samples showed that, under all irrigation regimes, the emitter output effectively reduced soil salinity, and that this reduction is more effective with frequent irrigations, washing the salts further away from the source. Further, the 0–25 cm deep layer was found to have the least salinity among the studied layers. All irrigation regimes (two, three, and fourday) were successful in controlling salinity in the root zone, but the twoday treatment, with a shallower irrigation depth and shorter irrigation intervals, offered the best leaching. The results of performance analysis in two years showed that the year did not have a significant effect on grain and dry matter yield. The results also showed that irrigation regimes did not have a significant effect on dry matter yield but significant on grain yield at 5%.