Biochar Simulate Aging And Its Potential Analysis On Improvement Of The Acid Red Soil

Red soil in Southern China,the annual average rainfall is heavy,soil eluviation is strong,and Al toxicity is serious.It is also the main distribution area of acid rain.Biochar can improve acidic soil pH,increase soil fertility,alleviate soil aluminum toxicity.Biochar is relatively stable under the natural state,after adding the biochar into the soil under rainfall leaching and acid rain soaked,the biochar aging effect will happen.In recent years,people focus on improvement of biochar on acid red soil and crop growth.The aim of this study was to investigate the aging process of peanut shells biochar by washing and acidification.The physic-chemical properties and structure of biochar and aged biochar were characterized by elemental analysis,scanning electron microscopy?SEM?,X-ray diffraction spectroscopy?XRD?and Fourier-transformed infrared spectroscopy?FTIR?.To study biochar physical and chemical properties and structure of the differences before and after aging.And the primary biochar,washing biochar and acidulated biochar fully mixed with acid red soil,to explore the potential of biochar alleviate soil aluminum toxicity and improve the soil nutrient.Planting pakchoi,study the potential of biochar promoting crop growth.Obtain the following results:?1?The pH of biochar declined after the two treatment,and the acidulated biochar?AB?dropped more than washing biochar?WB?.Moreover,the O/C and?O+N?/C ratio of WB decreased by 8.89%and 10.42%,but the ratioes of AB increased by 11.11%and14.58%respectively.These suggest that aging process changed the hydrophilicity and polarity of the biochar.In addition,compared with primary biochar?PB?,the total content of alkaline elements of WB and AB was reduced by 26.53%and 88.76%respectively,indicating that more alkaline elements were released after the biochar aging.?2?Compared with PB,the surface of the washing biochar was smoother and the microporous structure remained intactly.However,the surface of biochar was rough and microporous structure was disrupted severely after acidification.The content of the crystal structure of Al2SiO5 and SiO2 was decreased obviously during aging process.Compared with PB,the characteristic peaks at 1166,1082 cm^-11 appeared due to the aging process of the washing biochar,and the characteristic peaks at 1705,1622 and 1546 cm^-1appeared and the characteristic peaks at 466 cm^-11 disappeared due to the aging process of the acidulated biochar.Meanwhile the relative absorbance of other peaks was reduced,indicating that the amount of oxygen functional groups increased in the process of aging.At the same time,the other functional groups became less and the content of crystal was reduced.¹³C-NMR spectrum analysis shows that compared with the primary biochar,washing aging biochar map does not have obvious difference,the map of acidulated biochar has a big difference.The aliphatic carbon and carboxyl carbon increased after aging,and the aromatic carbon is reduced.?3?Aging biochar improved the content of soil available potassium and organic matter as compared to CK treatment.It also resulted in the increase of soil pH of PB and WB treatment by 0.17 and 0.16 units respectively,while decreased in AB by 0.44 units.Moreover,the total amount of exchangeable acidity in red soil treated by PB and WB reduced by 70.08%and 34.84%respectively,while augmented in AB treatment by 18.24%compared with CK treatment,indicating that the aging biochar did not effectively reduce the amount of active acid and potential acid in soil,and acidulated biochar even aggravated soil acidification.?4?Compared with CK treatment,the treatments of PB and WB in red soil increased the content of humic acid aluminum,colloidal aluminum ions and the polymers hydroxyl ion by 8.59%and 2.87%?20.17%and 14.46%?101.65%and 32.92%,while the soil exchangeable Al³⁺content decreased by 81.87%and 49.15%respectively.However,the soil exchangeable Al³⁺and colloid aluminum ion content in AB treatment elevated by17.98%and 20.67%,while the single dimer hydroxyl aluminum ions and humic acid contents decreased by 40.69%and 49.79%severally.These results indicated that washing aging biochar can reduce the content of bio-toxic Al³⁺,and the acidulated aging biochar increase the content of Al³⁺instead.Also illustrate that the transformation of different forms of aluminum before and after the aging biochar treatment changed the proportion of Al forms in the soil,but colloidal aluminum ions remained the main form of active aluminum.?5?The biochar can also significantly increase the content of rapidly available potassium,rapidly available phosphorus,and organic carbon in red soil,after biochar aging,the trend of increasing soil available nutrients was receded.Although biochar aging,the soil improvement effect is abate,but there is no greater influence on the amount and type of functional groups of soil.Meanwhile Biochar can promote the growth of pakchoi,improve the elements of pakchoi,and reduce the content of aluminum in the pakchoi,alleviate aluminum poisoning to pakchoi.But after biochar aging,to promote the pakchoi growth weakened,improve pakchoi element content and lower aluminum content in pakchoi is abate,even exacerbate poison to pakchoi.