Amelioration Of An Ultisol Acidity By Biochars Derived From Canola Straw Varied With Their Cultivating Soils

A large amount of agricultural waste was produced in agriculture,of which the annual production of crop straw was estimated about 0.8 billion tons in China.However,it seems unrealistic to return all of crop straws back to the agricultural fields,due to the strong interference effects of straws on agricultural operations.Moreover,slash-and-burn cultivation has led to increasing environmental risk of air pollution.On the other hand,the acidified soils are widely distributed in the south of China,and soil acidification from inappropriate agriculture schemes has worsened,especially in the tropical and subtropical regions of southern China.Soil acidification greatly inhibited the sustainability of agricultural production.In detail,soil acidification is a typical soil degradation,resulted in soil quality degradation,nutrient loss,toxic elements release and activation,and crop yield reduction.Therefore,a highly efficient and environmentally friend soil modifier aiming to reduce the degree of soil acidification was required for satisfactory crop production.More recently,results showed that crop straw biochars are characterized by alkaline,great potential to increase the acid soil pH and correct soil acidity.Besides,the biochars are rich in C and the nutrient elements,such as N,P,K,Ca and Mg,and can be applied to improve soil fertility.In addition,crop straw derived biochars have higher stability due to more resistant to decomposition than their precursors.Increasing attention has been focused on the use of biochars as soil additives in agriculture,such as amending soil acidity,improving soil quality and increasing crop yield.The species and amounts of cations,and its uptake by the plants varied with cultivating soils.Generally,the acid soil is highly weathered and leached,and thus contains insufficient base cations for plant growth.Hence,the base cations and alkaline substances in the crop straw biochars,and the ameliorating effects of these biochars on acidified soils should vary with the areas of crop straw collected.However,little information is available regarding the regional difference of crop straw derived biochars.In the present study,four canola straws collected from Yingtan in Jiangxi Province,Xuancheng in Anhui Province,Nanjing and Huaiying in Jiangsu Province,respectively.These straws were pyrolyzed at different temperatures under anaerobic condition.The pH values,the contents of alkalinity,base cations,carbonates,and total acid functional groups in these biochars were measured.The effect of canola straw biochars on the alleviation of aluminum toxicity was evaluated by wheat seeding root elongation experiment.The amelioration effects of canola straw biochars on correcting an Ultisol acidity were examined with incubation experiments.Results showed:(1)The contents of base cations in biochars,as well as biochars p H,the contents of carbonates,and alkalinities varied with their biomass planting soils.Yingtan canola straw biochar had the lowest p H value,contents of alkalinity,base cations,carbonate and total acid functional groups,followed by the biochars derived canola straw from Xuancheng,Huaiyin and Nanjing.Moreover,the properties of canola straw biochars were highly affected by the pyrolysis temperature.In a given straw feedstock,the p H value,the contents of alkaline base cations and carbonate of biochar increased progressively with increase in pyrolysis temperature.In contrast,the content acid functional groups decreased.(2)The results of hydroponics experiments indicated that canola straw biochar can be used to alleviate aluminum phytotoxicity.The alleviation effect varied with the canola planting area.The observations on the wheat seedling root elongation,Evans blue staining experiments,the remanent Al(III)and the p H value in the exposure solution and Al(III)distribution in the wheat seedling root,revealed that the effect of canola straw biocar on alleviation aluminum phytotoxicity followed the order: Huaiyin biochar > Nanjing biochar > Xuancheng biochar > Yingtan biochar.(3)The results of pH value,exchangeable base and exchangeable acid in the incubated soils amended with the above biochars indicated that,the amelioration effects of these biochars on an Ultisol acidity followed the order: Huaiying biochar > Nanjing biochar > Xuancheng biochar > Yingtan biochar.The order was consistent with the p H value,the contents of alkalinity,base cations and carbonate in these biochars,as well as the effect of alleviation aluminum phytotoxicity.Therefore,the amelioration effect of crop straw biochars on soil acidity depends not only on the pyrolysis condition and biomass feedstocks,but also on the areas of crop straw cultivated.