اثر روش‌های خاک‌ورزی بر برخی خصوصیات خاک و بهره‌وری آب در دو رقم چغندرقند

مصرف بهینه آب، انرژی و بهبود خصوصیات فیزیکی خاک از ویژگی‌های خاک‌ورزی حفاظتی است که در این مطالعه تاثیر آن بر عملکرد و بهره‌وری آب چغندرقند پاییزه طی دو سال زراعی 97-96 و 98-97 بررسی شد. برای این منظور آزمایشی به‌صورت کرت‌های نواری خردشده در قالب طرح بلوک‌های کامل تصادفی با سه تکرار در اراضی مرکز تحقیقات کشاورزی صفی‌آباد دزفول با بافت لومی رسی سیلتی اجرا شد. کرت اصلی شامل خاک‌ورزی مرسوم (ct)، چیزل (ch)، کم‌خاک‌ورزی (mt)، و بی خاک‌ورزی به صورت کاشت مستقیم در بقایای گندم (nt) و کرت فرعی شامل دو رقم پالما و شریف بود. آبیاری به‌صورت جویچه‌ای و با سیفون‌های هم قطر صورت گرفت. نتایج شاخص مخروطی (ci) و جرم مخصوص ظاهری خاک (bd) در لایه 100 برای کلیه روش‌های خاک‌ورزی مشابه و در یک سطح آماری قرار داشتند. مقادیر ci در عمق 2010 سانتی‌متر با میانگین 0.79 مگاپاسکال در یک سطح اما bd در تیمار nt با مقدار 1.7 گرم بر سانتی‌متر مکعب اختلاف معنی‌داری با سه روش دیگر خاک‌ورزی نشان داد. با این وجود هیچ یک از روش‌های خاک‌ورزی تاثیری در رشد و انشعاب ریشه چغندرقند نداشت. از طرفی درصد کربن آلی خاک، عملکرد و بهره‌وری آب چغندرقند، در تیمارهای خاک‌ورزی اختلاف معنی‌داری نداشتند. واکنش ارقام پالما و شریف به شیوه‌های خاک‌ورزی یکسان بود، حال آنکه بهره‌وری آب ریشه تر و شکر رقم پالما (به‌ترتیب 9 تن در هکتار و 1.2 کیلوگرم در متر مکعب) بالاتر از رقم شریف (به‌ترتیب 7.3 تن در هکتار و 1 کیلوگرم بر متر مکعب) بود. مجموع نتایج نشان داد که استفاده از کاشت مستقیم چغندرقند پاییزه در بقایای گندم امکان‌پذیر بوده و علاوه بر حذف آبیاری قبل از کاشت و کاهش تردد ماشین‌های خاک‌ورزی، با گزینش رقم مناسب می‌توان عملکرد کیفی را افزایش داد.

The Effect of Tillage Methods on some Soil Properties and Water Productivity of Two Sugar Beet Cultivars

Introduction: North of Khuzestan province is one of the major areas for autumn sugar beet planting. Conventional tillage (CT) is widely practiced by sugar beet growers in this region. CT in sugar beet consists of burning wheat residue, using deep plowing with a moldboard plow or ripper plowing followed by several passes of disking, leveling, and furrowing. These aggressive tillage practices have many negative consequences for soils. Losses of soil organic carbon decreases soil permeability and consequently increases soil erosion and surface runoff. Therefore, applying conservation agriculture principles in sugar beet planting, conservation of residues and elimination or reduction of tillage, can help to optimize water use management and improve soil health on a farm scale. The objectives of this study were (i) to determine the possibility of direct planting of autumn sugar beet in wheat residues, (ii) to estimate sugar beet yield and crop water productivity (WP) under CT, chisel (CH), minimum tillage (MT) and notillage (NT) systems, (iii) to evaluate the response of sugar beet cultivars (Sharif and Palma) to different soil tillage systems, and (iv) to determine the effect of soil tillage systems on some soil physical properties.Materials and Methods: A field experiment was conducted for two years (2016—2017) at the Safiabad Dezful Agricultural Research Center (32° 14.44´32°15.93´ and 48° 25.41´48°47). The soil of the study site was deep, welldrained with a silty clay loam texture. The mean annual precipitation and evaporation are 317 and 2400 mm, respectively, with an elevation of 108 m above mean sea level. Irrigation water was supplied from the Dez irrigation network without any salinity restrictions. The experimental was conducted in a splitplot arrangement based on a randomized complete block design with three replicates. The mainplot treatment was tillage method and the subplot treatment was two sugar beet cultivars (Palma and Sharif). Tillage treatments included conventional tillage (CT) (moldboard ploughing + MT steps), chisel (CH) (chisel ploughing + MT steps), minimum tillage (MT) (two perpendicular disks, fertilizing centrifugal machine, disking, furrowing, planting with pneumatic row planter), and notillage (NT) (spraying, planting with NT pneumatic row planter). The length and width of each plot were 100 and 6 m, respectively, and row spacing was 75 cm.Soil penetration resistance or cone index (CI) readings were recorded in 2 cm increments to a depth of 50 cm using SP1000 digital penetration tester to reflect the soil compaction. Soil bulk density was determined in 010 and 1020 cm layers. In the first and second year, sugar beet samplings were done 216 and 220 days after planting, by harvesting a row of 75 cm with length of 10 m (7.5 m2). WP was calculated by dividing the root and sugar yield to irrigation water and effective rainfall (effective rainfall was calculated every year with SCS method). Composite data analysis and mean comparison were performed with MSTATC statistical software.Results and Discussion: Results of CI showed no significant difference between four tillage methods at 010 cm depth. With increasing depth up to 30 cm, slight differences in soil compaction were observed for different tillage treatments, especially in the second year. Overall, compaction in the 050 cm profile in the CT and CH method were about 45% and 33%, respectively, lower than NT method, whereas in MT method it was about 37% higher than NT method. Results of root branch number analysis showed that the NT and CT treatments had the lowest branching (2.67 and 2.83, respectively) and the two CH and MT treatments had the highest branching (4.2 and 5.3, respectively). Therefore, NT had no negative effect on root growth of sugar beet. The results of bulk density measurements in the 010 cm layer were consistent with the results of the CI, but at depth of 1020 cm, NT method with the highest bulk density (1.71 g cm3) had significant difference with the other three tillage methods. Tillage method had no significant effect on root and sugar yield and root and sugar WP. However, in CT treatment, root yield increased by 68.5% and sugar yield by 612%, while root and sugar WP in NT treatment was about 8% higher than in the other three tillage treatments. On the other hand, changing climate conditions, especially rainfall during two years of the experiment, resulted in significant interaction between year and cultivar for yield and WP at 1% probability level. In the first year, the yield of Sharif cultivar (86.7 t ha1) was higher than Palma (80.2 t ha1), but in the second year, despite the decreasing yield of both cultivars, higher resistance of Palma cultivar to Cercospora disease resulted in a significant increase in sugar yield and WP over last year.Conclusion: The twoyear results of this study showed that the direct planting of autumn sugar beet in wheat residues (NT) is possible. Sugar beet yield and WP were not significantly different in tillage methods, but NT reduced tillage traffic from 7 times to 2 times and reduced energy consumption. The response of the two sugar beet cultivars to different tillage methods was the same and among them the Palma cultivar had the highest yield because of its higher resistance to Cercospora disease.