تعيين مقدار بقاياي گياهي، ويژگي‌هاي فيزيكي و مكانيكي خاك در سيستم‌هاي خاك‌ورزي مختلف

Determination of crop residues and the physical and mechanical properties of soil in different tillage systems

روش‌های خاك‌ورزی حفاظتی كه با مدیریت مناسب بقایای محصول همراه باشد یكی از راه‌كارهای مؤثر در جلوگیری از فرسایش خاك، كاهش آلودگی هوا، كاهش مصرف انرژی و كاهش هزینه‌ها در كشاورزی به‌شمار می‌رود. در این تحقیق، تأثیر روش‌های مختلف خاك‌ورزی بر پوشش بقایای گیاهی، مقاومت مكانیكی خاك و پایداری خاكدانه‌ها مورد بررسی قرار گرفت. همچنین تأثیر درصدهای مختلف بقایای گیاهی بر مقاومت غلتشی چرخ غیرمحرك در محیط انباره خاك مورد بررسی قرار گرفت. آزمایشات مزرعه‌ای به‌صورت فاكتوریل و در قالب طرح بلوك‌های كاملاً تصادفی انجام شد. روش‌های مختلف خاكورزی در سه تیمار (گاوآهن برگردان‌دار، گاوآهن بشقابی و گاوآهن چیزل) با چهار تكرار صورت گرفت. مقادیر بقایای گیاهی با استفاده از دو روش برش عرضیِ خطی و روش پردازش تصویر محاسبه گردید. آزمایشات مربوط به مقاومت غلتشی نیز در محیط انباره خاك و در سه سطح 10، 50 و 90 درصد انجام گرفت. نتایج نشان داد كه با افزایش شدت خاك‌ورزی، پایداری خاكدانه‌ها كاهش یافته است، به‌طوری‌كه كمترین مقدار پایداری خاكدانه‌ مربوط به تیمارهای خاك‌ورزی شده با گاوآهن برگردان‌دار و بیشترین مقدار پایداری مختص تیمار خاك‌ورزی شده با گاوآهن چیزل و بشقابی به‌دست آمد. نتایج حاصل از بررسی اثر بقایای گیاهی بر مقاومت غلتشی چرخ نشان داد كه مقاومت غلتشی تیمارهای مختلف با یكدیگر تفاوت معنی‌داری ندارند. در نهایت استفاده از گاوآهن بشقابی به‌دلیل داشتن درصد بالایی از پوشش بقایای گیاهی و كاهش چشمگیر مقاومت مكانیكی و جرم ویژه ظاهری و نیز حفظ پایداری خاكدانه‌ها، به‌عنوان ابزار مناسب خاك‌ورز در این تحقیق توصیه می‌شود.

Introduction: Monitoring and management of soil quality is crucial for sustaining soil function in ecosystem. Tillage is one of the management operations that drastically affect soil physical quality. Conservation tillage methods are one of the efficient solutions in agriculture to reduce the soil erosion, air pollution, energy consumption, and the costs, if there is a proper management on the crop residues. One of the serious problems in agriculture is soil erosion which is rapidly increased in the recent decades as the intensity of tillage increases. This phenomenon occurs more in sloping lands or in the fields which are lacking from crop residues and organic materials. The conservation tillage has an important role in minimizing soil erosion and developing the quality of soil. Hence, it has attracted the attention of more researchers and farmers in the recent years. Materials and Methods: In this study, the effect of different tillage methods has been investigated on the crop residues, mechanical resistance of soil, and the stability of aggregates. This research was performed on the agricultural fields of Urmia University, located in Nazloo zone in 2012. Wheat and barley were planted in these fields, consecutively. The soil texture of these fields was loamy clay and the factorial experiments were done in a completely randomized block design. In this study, effect of three tillage systems including tillage with moldboard (conventional tillage), tillage with disk plow (reduced tillage), chisel plow (minimum tillage) and control treatment on some soil physical properties was investigated. Depth is second factor that was investigated in three levels including 0-60, 60-140, and 140-200 mm. Moreover, the effect of different percentages of crop residues on the rolling resistance of non-driving wheels was studied in a soil bin. The contents of crop residues have been measured by using the linear transects and image processing methods. In the linear transects method, the experiments were replicated three times in each block due to increasing the accuracy and mean of datawas calculated. The tests were randomly performed in each block. Then, the number of nodes, which are located on crop residues of size 25 mm, longitudinally, was counted. So the percentage of crop residue in each block was calculated through the percentage of nodes. The experiments of rolling resistance were also performed in three levels, 10, 50, and 90% of crop residues, inside the soil bin. Results and Discussion: Result showed that, in comparison with control treatment, tillage operation significantly decreased bulk density (p <0.01), penetration resistance (p <0.01), and aggregates stability (p <0.01), in the soil surface (0-10 cm). Also, the results showed that penetration resistance of soil was increased by depth. The results of variance analysis in crop residue dataset showed that there were significant differences among the treatments in the terms of crop residues (P <0.05). Because of increasing the intensity of tillage and also the different performance of various tillage tools would mix crop residues with the soil and lead to reduce the crop residues. The consequences revealed that the treatments had significant differences in the terms of mechanical resistance of soil at the confidence level of 5%. The mechanical resistance of soil in three levels of depth had the most and the least contents in chisel and disk plows treatments, respectively. Because of disk plows can powder soil more than other treatments and chisel plows can only make narrow in the soil. The results of investigating the effect of crop residues on rolling resistance of wheels showed that there were not any significant differences between the treatments. Conclusions: It can be concluded that increasing the tillage intensity would reduce the stability of aggregates. Thus, the least stability of aggregates was obtained when using moldboard plows. However, the most stability was achieved using chisel and disk plows. Finally, disk plough is recommended as an appropriate tool in this research due to the high percentage of crop residues, lower mechanical resistance, lower bulk density, and higher stability of aggregates in the soil. Generally, in short-term period, conservation tillage (reduced tillage and minimum tillage) results the improvement of soil physical quality in comparison with tillage operation. Further studies on long-term effects of various tillage systems are suggested in order to select and implement of optimum tillage method in the region.