با همکاری انجمن آبخیزداری ایران

نوع مقاله : مقاله پژوهشی

نویسندگان

1 استاد، بخش تحقیقات حفاظت خاک و آبخیزداری، مرکز تحقیقات و آموزش کشاورزی و منابع طبیعی استان کرمانشاه، سازمان تحقیقات، آموزش و ترویج کشاورزی، کرمانشاه، ایران

2 دانشیار، بخش تحقیقات حفاظت خاک و آبخیزداری، مرکز تحقیقات و آموزش کشاورزی و منابع طبیعی استان کرمانشاه، سازمان تحقیقات، آموزش و ترویج کشاورزی، کرمانشاه، ایران

3 استاد، پژوهشکده حفاظت خاک و آبخیزداری، سازمان تحقیقات، آموزش و ترویج کشاورزی، تهران، ایران

چکیده

مقدمه
خاکورزی مهم‌ترین فعالیت کشاورزی در سراسر جهان است که نقش به‌سزایی بر کیفیت خاک، محیط‏زیست و عملکرد محصول دارد. در غالب دیم‌زارهای ایران شخم با گاوآهن برگرداندار و در جهت شیب دامنه انجام می‏‌گیرد که به‌دلیل نقش آن در انتشار کربن آلی، فرسایش خاک و کاهش عملکرد محصول زیان‌بارترین نوع خاک­ورزی است. بر اساس تحقیقات متعدد در نقاط مختلف جهان، شخم متداول با گاوآهن برگردان‏دار موجب آسیب جدی به ویژگی‏‌های مهم خاک، کاهش ذخیره رطوبت، افزایش هزینه، هدررفت عناصر غذایی، کاهش عملکرد محصول و نیز تبعات خارج حوضه‌‏ای متعدد ازجمله رسوب، سیل، آلودگی منابع آب، انتشار کربن آلی می‏‌شود که در شرایط تغییرات اقلیمی شدیدتر است. به‌‏طوری‌که به‌‏عنوان مبحثی جداگانه و مهم در فرسایش خاک تحت عنوان فرسایش شخم قلمداد شده است. هدف پژوهش نیز تعیین اثرات روش‌های شخم بر جرم مخصوص ظاهری، پایداری خاکدانه‏‌ها و فرسایش‌پذیری خاک بود که در معاونت تحقیقات دیم سرارود به مدت پنج سال (1401-1396) انجام یافت.
 
مواد و روش‌‏ها
این پژوهش در ایستگاه تحقیقاتی موصوف به سرارود (معاونت موسسه تحقیقات دیم کشور) انجام یافت. این ایستگاه در 15 کیلومتری شرق شهر کرمانشاه و سه کیلومتری راه اصلی کرمانشاه-تهران قررار دارد. این پژوهش در قالب طرح آزمایش‌های کرت‏‌های دوبار خرد شده بر پایه بلوک­‌های کامل تصادفی با سه تکرار انجام شد که متشکل از چهار تیمار اصلی (شخم متداول، خاکورزی مرکب، چیزل و کشت مستقیم) و سه تیمار فرعی (بدون بقایای گیاهی، 33 درصد بقایای گیاهی و 66 درصد بقایای گیاهی) بود. به‏‌منظور برررسی نتیجه تأثیر تیمارها در طول سال‌های اجرای طرح، محل تیمارهای اصلی و فرعی ثابت ماند و فقط تناوب کشت تغییر کرد. نمونه‌­های خاک از لایه صفر تا 20 سانتی‏‌متری برداشت شد و مورد آزمایشات جرم مخصوص ظاهری، کربن آلی و  پایداری خاکدانه‏‌ها (به روش الک تر) قرار گرفت. عامل فرسایش‏ از طریق محاسبه عامل فرسایش‌پذیری (K) در فرمول جهانی فرسایش خاک و بر اساس پنج عامل درصد مواد آلی، درصد سیلت + شن خیلی ریز (0.05 تا یک میلی‌‏متر)، درصد شن درشت (یک تا دو میلی‏‌متر)، ساختمان خاک و نفوذپذیری محاسبه شد. تجزیه آماری داده‌‏ها نیز با نرم‏‌افزار SAS انجام شد.

نتایج و بحث
متوسط جرم مخصوص ظاهری در تیمارهای اصلی شامل شاهد (شخم متداول)، خاک‌ورزی مرکب، چیزل و کشت مستقیم به‌ترتیب 1.62، 1.45، 1.40 و 1.37 گرم بر سانتی‏‌مترمکعب بود که به‏‌طور معنی‌داری در تیمار کشت مستقیم (0.05p<) کمتر بود. تیمارهای فرعی (نسبت بقایای گیاهی) نیز تأثیر معنی‌‏داری بر جرم مخصوص ظاهری داشتند، به‏‌طوری‌که تأثیر هر دو نسبت 33 و 66 درصد کاه (بقایای محصول) در کاهش آن معنی‌‏دار بود. تأثیر تیمارها بر جرم مخصوص ظاهری از سال سوم به بعد معنی‏‌دار بود. همچنین نتایج تجزیه آماری تأثیر تیمارهای نوع شخم و نسبت بقایای گیاهی بر کربن آلی خاک در تیمارهای اصلی شامل شاهد (شخم متداول)، خاک‌ورزی مرکب، چیزل و کشت مستقیم ‏به‌ترتیب 1/20، 1/50، 1/40 و 1/70 درصد به‌‏دست آمد که با هم تفاوت معنی‏‌داری داشتند (0.05p<)، اما تأثیر کشت مستقیم بر افزایش کربن آلی خاک بیشتر بود. تیمارهای فرعی (نسبت بقایای گیاهی) نیز تأثیر معنی‏‌داری بر کربن آلی خاک داشتند، به‏‌طوری‌که تأثیر هر دو نسبت 33 و 66 درصد کاه (بقایای محصول) در کاهش آن معنی‌‏دار بود. نسبت خاکدانه‏‌های خیلی ریز در تیمار کشت مستقیم و با بیشترین بقایای گیاهی به‏‌طور معنی‌‏داری کمتر بود. مقدار خاکدانه‏‌های متوسط در سطح تیمارها با هم تفاوت معنی‏‌داری نداشتند. خاکدانه‏‌های خیلی درشت کشت متداول و تیمار فرعی بدون بقایای محصول به‏‌طور معنی‏‌داری کمتر بود. اندازه خاکدانه‏‌های خاک در سال سوم و عمدتاً در چهارم معنی‏‌دار بود. به‏‌عبارتی افزایش خاکدانه‌‏های درشت و خیلی‌درشت و به همان نسبت کاهش خاکدانه‏‌های ریز و خیلی‌ریز از سوم به بعد نمایان شده است. نتایج بیانگر نقش مؤثر روش‌‏های مختلف خاکورزی حفاظتی در کاهش فرسایش‌‏پذیری خاک در مقایسه با خاکورزی متداول است. نتایج این پژوهش نشان داد که سه روش خاکورزی حفاظتی نقش مؤثری در بهبود ویژگی‌‏های مورد ارزیابی خاک داشتند. البته که نقش کشت مستقیم (بدون شخم) در این روند برجسته‌‏تر بود. به­‌طوری­که در نتایج اشاره شد، با گذشت زمان از اجرای پژوهش، به‏تدریج کربن آلی و نسبت خاکدانه‏‌های درشت (یک تا دو میلی‌‏متر) و خیلی درشت (دو تا 4.6 میلی‏‌متر) در تیمارهای خاک­ورزی حفاظتی افزایش یافت.
 
نتیجه‏‌گیری
خاکورزی حفاظتی به‌همراه باقی گذاشتن بقایای گیاهی در خاک به‌‏طور معنی‏‌داری موجب بهبود مهم‌ترین ویژگی‏‌های کیفیت خاک مورد اندازه‏‌گیری شدند که شامل کربن آلی، جرم مخصوص ظاهری و نسبت خاکدانه‏‌های درشت خاک بود. بی‏‌خاک­ورزی (کشت مستقیم) با یک‏‌سوم بقایای گیاهی (33 درصد) به‏‌عنوان مناسب‏ترین روش شخم در شرایط دیم و تناوب گندم و نخود که در غالب مناطق نیمه‏‌خشک کشور مرسوم است به‌‏عنوان تیمارهای مناسب این پژوهش ارائه می‏‌شود.
 

کلیدواژه‌ها

عنوان مقاله [English]

Effects of tillage practice and crop residue retention on soil organic carbon, bulk density and aggregate and erodibility

نویسندگان [English]

  • Mosayeb Heshmati 1
  • Mohamad Gheitury 2
  • Yahya Parvizi 3

1 Professor, Kermanshah Center for Agricultural and Natural Resources Research and Education, Agricultural Research, Education and Extension Organization (AREEO), Kermanshah, Iran

2 Associate Professor, Kermanshah Center for Agricultural and Natural Resources Research and Education, Agricultural Research, Education and Extension Organization (AREEO),Kermanshah, Iran

3 Professor, Soil Conservation and Watershed Management Research Institute, Agricultural Research, Education and Extension Organization (AREEO), Tehran, Iran

چکیده [English]

Introduction
Tillage is the most significant agricultural practice worldwide, playing a crucial role in soil quality, the environment, and crop yield. In the majority of Iran's rainfed farmlands, tillage is performed using moldboard plows and along the slope gradient. Due to its role in organic carbon depletion, soil erosion, and reduced crop yield, this method is considered the most detrimental form of tillage. Based on numerous studies worldwide, conventional tillage using a moldboard plow severely damages key soil properties, reduces moisture retention, increases costs, leads to nutrient loss, decreases crop yield, and causes numerous off-site consequences such as sedimentation, flooding, water pollution, and organic carbon depletion, these impacts are exacerbated under climate change, making it a distinct and critical issue in soil erosion, specifically termed tillage erosion. The aim of the study was to determine the effects of tillage methods on bulk density, aggregate stability, and soil erodibility, conducted at the Sararoud Dryland Agricultural Research sub-institute over a five-year period (2017–2022).
 
Materials and methods
This research was conducted at the Sararood research station (Dryland Agricultural Research sub-institute). The station is located 15 km east of Kermanshah city and 3 km from the main Kermanshah-Tehran road. This research was conducted as a split-split plot experiment based on a randomized complete block design with three replications. The experiment consisted of four main treatments (conventional tillage, combined tillage, chisel tillage, and no-tillage) and three sub-treatments (no plant residue, 33% plant residue, and 66% plant residue). To evaluate the long-term effects of the treatments, the locations of the main and sub-treatments remained fixed throughout the study period, with only the crop rotation being altered. Soil samples were collected from the 0-20 cm depth layer and analyzed for bulk density, organic carbon, and aggregate stability (using the wet sieving method). The erosion factor was calculated by determining the erodibility factor (K) in the Universal Soil Loss Equation, based on five parameters: organic matter content, percentage of silt + very fine sand (0.05–1 mm), percentage of coarse sand (1–2 mm), soil structure, and permeability. Statistical analysis of the data was performed using SAS software.
 
Results and discussion
The mean bulk density in the main treatments, including control (conventional tillage), combined tillage, chisel tillage, and no-tillage, was 1.62, 1.45, 1.40, and 1.37 g/cm³, respectively, with a significant decrease (p < 0.05) observed in the no-tillage treatment. The sub-treatments (crop residue levels) also had a significant effect on bulk density, with both 33% and 66% straw (crop residue) rates significantly reducing it. The effect of treatments on bulk density became significant from the third year onward. The statistical analysis also revealed the effects of tillage methods and crop residue levels on soil organic carbon. In the main treatments—control (conventional tillage), combined tillage, chisel tillage, and no-tillage—soil organic carbon content was 1.20%, 1.50%, 1.40%, and 1.70%, respectively, these values showed significant differences (p < 0.05), with no-tillage having the greatest effect on increasing soil organic carbon. The sub-treatments (crop residue levels) also had a significant effect on soil organic carbon, with both 33% and 66% straw (crop residue) rates significantly increasing it. The proportion of very fine aggregates was significantly lower in the no-tillage treatment with the highest crop residue level. The amount of medium-sized aggregates did not differ significantly among the treatments. The proportion of very large aggregates was significantly lower in conventional tillage and the sub-treatment without crop residue. The size of soil aggregates became significant in the third year and predominantly in the fourth year. In other words, an increase in large and very large aggregates and a corresponding decrease in fine and very fine aggregates were observed from the third year onward. The results indicate the effective role of various conservation tillage methods in reducing soil erodibility compared to conventional tillage. The results of this study showed that the three conservation tillage methods played an effective role in improving the evaluated soil properties. Certainly, the role of no-tillage (without plowing) was more prominent in this process. As indicated in the results, over time following the implementation of the study, organic carbon and the proportion of large (1–2 mm) and very large (2–4.6 mm) aggregates gradually increased in the conservation tillage treatments.
 
Conclusions
Conservation tillage combined with retaining crop residues significantly improved the most important measured soil quality properties, including organic carbon, bulk density, and the proportion of large soil aggregates. No-tillage (direct seeding) with one-third crop residue (33%) is recommended as the most suitable tillage method under rainfed conditions and wheat-chickpea rotation, which is common in most semi-arid regions of the country, and is proposed as the optimal treatment in this study.
 

کلیدواژه‌ها [English]

  • Chisel tillage
  • Crop residue
  • Combined tillage
  • No tillage
  • Winter wheat
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