پديد آورندگان :
ابريشم كش، سپيده دانشگاه گيلان - دانشكده كشاورزي - گروه علوم خاك، رشت , فاضلي سنگاني، محمود دانشگاه گيلان - دانشكده كشاورزي - گروه علوم خاك، رشت , رمضان پور، حسن دانشگاه گيلان - دانشكده كشاورزي - گروه علوم خاك، رشت , نوروزي، مهدي دانشگاه تبريز - دانشكده كشاورزي , شعباني، عباس دانشگاه گيلان - دانشكده كشاورزي - گروه علوم خاك، رشت
كليدواژه :
پايداري خاكدانه , پوسته شلتوك برنج , تزريق سوسپانسيون بيوچار , سرشاخه هرس شده درخت زبان گنجشك , كربن آلي
چكيده فارسي :
درسالهاي اخيراستفاده از بيوچار، به عنوان يك ماده اصلاحي با هدف كاهش فرسايش خاك مورد توجه قرار گرفته است. در اين پژوهش اثر تزريق بيوچار به صورت سوسپانسيون بر ويژگيهاي فيزيكي و شيميايي دو نوع خاك مارني حساس به فرسايش در جنوب گيلان مورد بررسي قرار گرفت. براي اين منظور، ابتدا دو نوع بيوچار از چوب سرشاخه هاي هرس شده درخت زبان گنجشك WB)) و پوسته شلتوك برنج (RB) توليد و مشخصه يابي شد و سپس در دو سطح 0/7 و 1/4 درصد به صورت سوسپاسيون آبي به دو نوع خاك مستعد فرسايش اضافه شد. اثر افزودن بيوچار بر ويژگي هاي فيزيكي و شيميايي دو خاك لوم و لوم شن مورد بررسي قرار گرفت. مقايسه خصوصيات بيوچارها نشان داد كه WB در مقايسه با RB داراي نسبت مولي هيدروژن به كربن و اكسيژن به كربن كمتري است كه نشان دهنده حضور كربن آروماتيك بيشتر و مقاومت بيشتر اين نوع بيوچار در برابر تجزيه است. نتايج نشان داد افزودن بيوچار به صورت سوسپانسيون آبي ميتواند علاوه بر جلوگيري از دستخوردگي خاك حساس به فرسايش به هنگام اضافه نمودن بيوچار به خاك، موجب افزايش كربن آلي و بهبود ضريب آبگذري و افزايش خاكدانه سازي خاك گردد. به طوري كه كاربرد هر دو نوع بيوچار موجب افزايش كربن آلي خاك هاي مورد مطالعه شد. اگرچه بيوچار چوب به دليل دارا بودن محتواي كربن بيشتر، تأثير بيشتري را در اين رابطه نشان داد. كاربرد هر دو نوع بيوچار در خاك داراي بافت درشت تر (لوم شن) و با ضريب آبگذري بيشتر موجب كاهش ضريب آبگذري خاك شد. در حالي كه بيوچار حاصل از چوب، موجب افزايش ضريب آبگذري خاك لوم شد. علاوه براين تأثير بيوچار بر افزايش پايداري خاكدانه در خاك لوم معني دار بود. به طور كلي پيامد افزودن بيوچار بر ويژگي هاي خاك بسته به نوع بيوچار مورد استفاده، سطح افزودن بيوچار و همچنين نوع خاك متفاوت است.
چكيده لاتين :
1- Introduction
Addition 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 erosion-prone 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 erosion-prone soils in southern Guilan.
2- Methodology
Two erosion-prone 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 63-250
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 20-25°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 & Conclusions
WB 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.
