چکیده:
تخریب خاک بهعنوان تهدیدی فزاینده در کشاورزی پایدار است. پژوهش حاضر با هدف بررسی اثر کاربرد سطوح مختلف، مواد اولیه و اندازه ذرات زغال زیستی بر برخی خصوصیات فیزیکی و مکانیکی یک خاک درشت بافت (لوم شنی) انجام شد. پژوهش در گلخانه تحقیقاتی دانشگاه شیراز در سال 1398-1399 انجام شد. بهمنظور بررسی اثر منابع، سطوح و اندازة ذرات زغال زیستی بر جرم مخصوص ظاهری خاک، پایداری خاکدانهها (میانگین وزنی قطر خاکدانهها)، مقاومت فروروی و مقاومت برشی خاک از دو نوع زغال زیستی برگ نخل و تفاله لیمو ترش که به مدت سه ساعت در دمای 500 درجه سانتیگراد گرماکافت شده بودند، استفاده شد. هرکدام از زغال های زیستی به سه کلاس اندازه ذرات کوچکتر از 0/8، 0/8 تا 2 و 2 تا 4 میلیمتر تفکیک شد و در چهار سطح کاربرد 0/5، 1، 2 و 4 درصد وزنی با خاک به همراه تیمار شاهد مورد استفاده قرار گرفت. گلدانها در شرایط استاندارد و تا حدود نزدیک رطوبت ظرفیت زراعی به مدت 15 ماه نگهداری شدند. نتایج نشان داد کاربرد زغالهای زیستی سبب بهبود خصوصیات فیزیکی خاک شده است بدین ترتیب که کاهش معنادار (p<0. 05) جرم مخصوص ظاهری خاک از 5/4 تا 19/8 درصد در کاربرد سطوح 0/5 تا چهار درصد زغالهای زیستی، افزایش پایداری خاکدانه از 37/6 تا 73/6 درصد و افزایش مقاومت برشی از 3/2 تا 15 درصد در کاربرد یک تا چهار درصد زغالهای زیستی در مقایسه با شاهد شده است. در کاربرد سطح چهار درصد زغالهای زیستی مقاومت نفوذی پنج درصد افزایش یافت. زغال زیستی تفالة لیمو در بهبود جرم مخصوص مخصوص ظاهری خاک موثرتر بوده، اگرچه زغال زیستی برگ نخل بر پایداری خاکدانهها و مقاومت برشی اثرگذارتر بود. اختلاف معناداری در اثر کاربرد منابع مختلف زغال زیستی بر مقاومت نفوذی خاک مشاهده نشد. صرفنظر از منابع زغالزیستی، در سطوح یکسان، ذرات ریزتر زغال زیستی (کوچکتر از 0/8 میلیمتر)، در پایداری خاکدانهها و مقاومت برشی موثرتر بودند، ولی ذرات درشت (4-2 میلیمتر) اثر بیشتری بر جرم مخصوص ظاهری خاک داشتند. نتایج این پژوهش میتواند در انتخاب زغال زیستی مناسب از نظر تاثیر بر کیفیت فیزیکی و مکانیکی خاک استفاده شود.
Introduction Increasing agricultural production is necessary due to the growing population in order to ensure food security. Also, a large part of agricultural lands in arid and semi-arid climates face the limitation of carbon storage and nutrients. This limitation is more visible in coarse textured soils with low clay content, due to the inability to supply elements required for plant growth and the ability to retain water in the soil. Therefore, modifying the physical, chemical and biological characteristics of the soil is inevitable to achieve sustainable agriculture. In the meantime, with the high use of chemical fertilizers along with the excessive tillage activities while destroying the soil, management costs increase. Soil degradation is an increasing worldwide threat to the sustainability of agriculture. The use of organic amendments like biochar may prove a key for sustainable agriculture, as it could keep the carbon pool in soil over the long term, thus improving soil fertility and crop productivity, mitigating global climate change, and finally enhancing soil physicochemical quality. The ability of biochar to enhance the physical and mechanical properties of soils is dependent on the characteristics of biochar including its particle size, application rate, feedstock type, and pyrolysis conditions. This study aimed to assess the effect of applying different application rates, feedstock, and particle sizes of biochar on the soil’s physical and mechanical properties in sandy loam soil. Materials and Methods The study was conducted in a research greenhouse of Shiraz University in 2019. To investigate the effect of biochar feedstock, application rate, and particle size on soil bulk density, aggregate stability (mean weight diameter), penetration resistance, and shear strength in sandy loam soil, using two feedstock types (palm leaf biochar and lemon peel biochar) were pyrolyzed at a temperature of 500 °C for 3 h. Each biochar was fractioned by dry sieving into three sizes: 2-4, 0.8-2, and Results and Discussion This result indicated that applying biochar improved the physical properties of soil, including a significant decrease in soil bulk density from 5.4 to 19.8% by using application rates of 0.5 to 4% biochar, increase aggregate stability from 37.6 to 73.6% and increase shear strength from 3.2 to 15 by using application rates of 1 to 4% of biochar as compared to control. For a 4% biochar rate, penetration resistance increased by 5% as compared to control. The results show that lemon peel is more efficient in soil bulk density whereas palm leaf biochar was efficient in aggregate stability and shear strength (no significant difference in penetration resistance was observed with the application of different biochar sources). Moreover, irrespective of biochar sources, biochar with finer particle sizes ( Conclusion Biochar as a type of organic compound that has great compatibility with the environment, is of interest in advanced agriculture due to its stable carbon storage and its positive effects on the biochemical and physical characteristics of the soil. According to the results of this research, the use of biochar in soil had a significant effect on reducing the apparent specific mass of the soil and also a significant increase in the stability of soil grains and shear resistance, which improves the physical and mechanical properties of the soil can have an effect on protecting the soil against water and wind erosion. On the other hand, although at the application level of 4% biochar, the resistance to subsidence increased by a significant amount of 5%, but no significant changes were observed in this feature. Palm leaf biochar had a stronger role in increasing the stability of soil grains and shear resistance, on the other hand, lemon pomace biochar had a greater effect in reducing specific mass due to its structure similar to sand particles. Also, by increasing the levels of biochar to four percent as the most effective level of biochar application, the apparent specific mass values decreased by 19.8% and the stability of soil grains and shear strength increased by 73.6% and 15% respectively. Also, the results showed that in general, by reducing the size of biochar particles from 4 mm to less than 0.8 mm, the weight average of soil grain diameter and shear strength increased significantly, but the average apparent specific mass increased with the increase of particle size (2-4 mm particles) reduced. Based on the above results, it can be concluded that choosing an optimal mode of sources, levels and size of biochar particles as an organic soil conditioner can lead to maximum productivity in agricultural production while reducing agricultural management costs. In this research, it was found that under the same conditions, the use of two percent palm leaf biochar with a particle size of less than 0.8 mm in sandy loam soil is useful. It should be kept in mind that the behavior of biochar is not only limited to the characteristics investigated in this research, and the change in the conditions of biochar production (thermal heating) causes a change in the characteristics of biochar. Therefore, it is suggested that in addition to the studied effects, the effects of characteristics based on the biochar production process, such as temperature and duration of thermodilution, should be investigated at different times on the physical, chemical and biological characteristics of different soils and in field conditions in order to obtain more comprehensive information on the optimal amounts of charcoal. Biologically, especially at the farm scale, to obtain soil amendment.