اثر کاربرد سوسپانسیون بیوچار بر ویژگی های فیزیکوشیمیایی دو خاک حساس به فرسایش

درسالهای اخیراستفاده از بیوچار، به عنوان یک ماده اصلاحی با هدف کاهش فرسایش خاک مورد توجه قرار گرفته است. در این پژوهش اثر تزریق بیوچار به صورت سوسپانسیون بر ویژگی های فیزیکی و شیمیایی دو نوع خاک مارنی حساس به فرسایش در جنوب گیلان مورد بررسی قرار گرفت. برای این منظور، ابتدا دو نوع بیوچار از چوب سرشاخه های هرس شده درخت زبان گنجشک wb)) و پوسته شلتوک برنج (rb) تولید و مشخصه یابی شد و سپس در دو سطح 0/7 و 1/4 درصد به صورت سوسپاسیون آبی به دو نوع خاک مستعد فرسایش اضافه شد. اثر افزودن بیوچار بر ویژگی های فیزیکی و شیمیایی دو خاک لوم و لوم شن مورد بررسی قرار گرفت. مقایسه خصوصیات بیوچار ها نشان داد که wb در مقایسه با rb دارای نسبت مولی هیدروژن به کربن و اکسیژن به کربن کمتری است که نشان دهنده حضور کربن آروماتیک بیش تر و مقاومت بیشتر این نوع بیوچار در برابر تجزیه است. نتایج نشان داد افزودن بیوچار به صورت سوسپانسیون آبی می تواند علاوه بر جلوگیری از دست خوردگی خاک حساس به فرسایش به هنگام اضافه نمودن بیوچار به خاک، موجب افزایش کربن آلی و بهبود ضریب آبگذری و افزایش خاکدانه سازی خاک گردد. به طوری که کاربرد هر دو نوع بیوچار موجب افزایش کربن آلی خاک های مورد مطالعه شد. اگرچه بیوچار چوب به دلیل دارا بودن محتوای کربن بیشتر، تاثیر بیشتری را در این رابطه نشان داد. کاربرد هر دو نوع بیوچار در خاک دارای بافت درشت تر (لوم شن) و با ضریب آبگذری بیشتر موجب کاهش ضریب آبگذری خاک شد. در حالی که بیوچار حاصل از چوب، موجب افزایش ضریب آبگذری خاک لوم شد. علاوه بر این تاثیر بیوچار بر افزایش پایداری خاکدانه در خاک لوم معنی دار بود. به طور کلی پیامد افزودن بیوچار بر ویژگی های خاک بسته به نوع بیوچار مورد استفاده، سطح افزودن بیوچار و همچنین نوع خاک متفاوت است.

Effect of biochar suspension application on physicochemical properties of two erosion-prone soils

Extended abstract1 IntroductionAddition of biochar to soil has been recently considered as an amendment to reduce soil erosion. Biochar contains pyrogenic carbon, which is produced by heating residue of various crops, woods (or in other words various biomass) in restriction or absence of oxygen. Biochar can affect soil organic matter level and aggregate stability. Reduction of soil erosion through maintenance and the increase of organic matter, increase of aggregate stability and improvement of hydraulic conductivity, and enhancement of moisture retention as a result of biochar application should be considered as an important achievement. It is important to study the effect of the different methods of biochar addition to the soil. The method of uniformly mixing biochar with surface soil which has been used in most studies can disturb the natural structure and lead to soil degradation. Therefore, it is an important issue to introduce a practical method that is associated with minimal soil manipulation, especially in erosionprone soils. The effect of the biochar addition as suspension in water has never been reported in previous studies. Therefore, the aim of this study was to investigate the effects of adding different levels of biochar produced from two types of feedstocks (horticulture and agriculture wastes) in form of aqueous suspension on the properties of two types of erosionprone soils in southern Guilan. 2 MethodologyTwo erosionprone soils which were undisturbed, were sampled by metal cylenders (diameter and height of 25 and15 cm, respectively) of marl lands located in southern guilan. These soils were named as SL and L. Texture of SL and L were sandy loam and loam, respectively. Two types of biochar were produced from different feedstocks including pruned branches of ash tree (Fraxinus excelsior) and rice husk by slow pyrolysis at a temperature of 550 °C in a muffle furnace, titled as WB and RB respectively. The yield of biochar was determined based on weight of biochar produced per unit weight of raw material. The amount of ash in the biochar was determined by heating five grams of biochar at 500 °C for more than 8 hours and weighing it again. The pH and electrical conductivity were measured in a mixture of biochar and deionized water with a weight ratio of 1: 20 (biochar: water). The total amount of carbon, hydrogen, and nitrogen in biochars was determined by dry combustion. Two types of produced biochars were milled with a particle size of 63250 microns, at levels of 0.7 and 1.4% by weight. Three repetitions in the form of aqueous suspensions were added to the cylinders containing undisturbed soil. Three cylinders of soil without biochar were also considered as control treatment. Soil cylinders were placed in a greenhouse for six months at a temperature range of 2025 °C and underwent several cycles of drying and wetting. At the end of incubation period, soil samples were obtained from cylinders. Soil properties including pH, electrical conductivity, organic carbon, hydraulic conductivity and aggregate stability were also measured. Thin sections were also taken out of soils and state of soil structure and voids were studied. The effect of two factors, including biochar type and biochar application level were analyzed as factorial in a completely randomized design by SAS statistical software. The comparison of the means was done by Duncan's test at the probability level of five percent.3 Results The WB compared to RB, had a higher yield, and less ash content, pH, electrical conductivity and H/C and O/C. More mineral ash in biochar is likely to provide more electrical conductivity in RB. Both biochar had an alkaline pH (more than 7). The biochar used in previous studies were usually alkaline, but biochar can be produced with any pH in the range of 4 to 12. The raw biomass has a H/C molar ratio of about 1.5, but with the pyrolysis, this ratio decreases. WB had less H/C compared to RB. Therefore, it can be concluded that WB had more aromatic carbon and it can probably be a more effective tool for carbon sequestration in soil. Presence of a lot of pores in biochar, especially WB which were visible in SEM photos, are very effective on vital soil functions such as aeration and hydrology. The organic carbon content of SL and L soils were significantly higher at biochar treatments compared to control. The hydraulic conductivity of SL soil at both application levels of WB and RB was significantly lower than the control. However, both application levels of WB and 1.4% of RB led to significant increase and decreases of hydraulic conductivity of L soil, respectively. The mean comparison showed no difference between bulk density of treatments and application levels of biochar to control treatment of SL soil. However, Bulk density of biochar treated L soils were less than control. Biochar treatment also result in significant increase of: mean weight and geometric mean diameter and decrease of fractal dimension of aggregates in L Soil.4 Discussion ConclusionsWB and RB biochars had no significant effects on indexes of soil aggregate stability and bulk density of SL soil, but they led to significant improvement of bulk density and aggregate stability of L Soil. Although, assessment of thin section showed partial improvement of soil structure of both SL and L soils. Therefore, more time than 6 months of incubation probably is needed to significant improve of aggregate stability of SL. Application of both biochars led to increase of organic carbon of both SL and L soils. Hydraulic conductivity was decreased in SL soil as result of both biochar application which can lead to the increase of water retention. Although the increase of hydraulic conductivity of L soils due to WB can be considered as a suitable approach for the decrease of the runoff, Generally, it can be concluded that due to the significant effect of feedstock type on biochar characteristics and different characteristics of soils, various types of biochar do not have a similar effect on a particular soil, therefore, a type of biochar cannot have the same effect on different types of soil.