Methodology Of Soil Organic Matter After Biochar Application

When soil organic matter was analyzed with the traditional method for soils with biochar applied,the content would show an abnormal increase.This is due to the interference of the biochar applied,which can also be oxidized and be added into the soil organic matter content.This will cause problems in soil fertility evaluation with soil organic matter as an index.So in order to solve this problem,the traditional oil organic matter determination method need to be modified.In this paper attempts were taken to improve the potassium dichromate oxidization method from the selection of digestion temperature and digestion time.The main results are as following:1.The proportion of soil organic matter and biochar digested was at different temperatures.Temperatures of 140℃ and 180℃ are the key temperature that can separate soil organic matter and biochar.Soil organic matter could be digested partly at 140℃,while no biochar could not be digested.At 180℃,the soil organic matter could be completely digested and most biochar could also be digested.Digesting time was also an important factor affecting the result.When the digesting time exceeded 5min at 180℃,the soil organic matter could be completely oxidized by the mixed solution of potassium dichromate and sulfuric acid,while biochar could be completely oxidized only when the digesting time exceeded 13 min.For the same digesting time,the higher the digestion temperature was,the larger the proportion of the total amount of carbon in the sample that could be digested.However,when the digestion temperature was higher than 180℃,the amount of soil organic matter that could be digested would not increase with the increase in temperature.2.Under the condition that the digestion temperature does not exceed 180 ℃ and the digestion time does not exceed 15 min,soil type,soil texture,and soil organic matter level had no significant influence in the digestion of soil organic matter and biochar in potassium dichromate and sulfuric acid mixed solution.Biochar types also had no significant effects onthe digestion of organic matter and biochar.3.Based on the results of the former experiments,an improved method was designed for the determination of soil organic matter content for soils with biochar applied.The improved method changed the original one-step determination into two-step determination.Two soil samples were taken for on soil.One sample was digested at 140℃ for 5 minutes and the other was digested 180℃ for 13 minutes.Soil organic matter and biochar content could be calculated according to the amount of carbon digested in the two steps and the empirical proportion of organic matter and biochar that could be digested at different temperatures.The digestion ratio of soil organic matter at 140℃ was 0.33 and the digestion ratio of biochar at180℃ was 0.77.4.The method verification test showed that the accuracy of the improved method for the determination of soil organic matter content for soils after biochar applied was significantly improved compared with the traditional method The relative error of the measured value of organic matter in the soil with 1% biochar applied decreased from about 21% to about 1%.