| Yellow soil is the main soil type for dry grain crop production in Guizhou,and its dry grain production accounts for about 60%of the province’s dry grain output.However,the existing problems of low fertility of yellow soil has being limited the sustainable development of dry farming.In order to organically combine high-value utilization of waste straw with fertilizer cultivation of yellow soil,rape-,rice-and corn straw were carbonized at 500℃as additive materials,and yellow soil with typical low fertility in Guizhou province was taken as the object of improvement.Indoor culture experiment had conducted for two years to analyze and compare the changes of soil p H,nutrients and key enzyme activities closely related to yellow soil fertility with different additive levels(0%,1%,2%and 4%).Finally,the integrated Fertility Index(IFI)was calculated by fuzzy mathematics,and the effects of different treatments on soil Fertility were evaluated quantitatively by IFI and the optimal treatment was selected.The main results were as follows:(1)Straw biochar was an alkaline or strongly alkaline carbon-rich product,especially rape straw biochar,with a p H of 8.23-9.55 and a total carbon content of 521.70 g/kg.In addition,rape straw biochar also had great aromaticity,hydrophilicity and polarity.There were significant differences in the specific surface area,total pore volume and average pore size of the three types of straw biomass chars(P<0.05),and their maxima appeared on corn straw biochar(160.20 m~2/g),rice straw biochar(30.10 ml/g)and rape straw biochar(1.69 nm),respectively.(2)The addition of different straw biochar significantly increased elements content of yellow soil,includ soil p H,organic matter,available NPK and total NPK etc.In particular,soil organic matter content was increased by more than 87%by adding corn straw biochar;followed by available phosphorus content,which increased by 24.4%to 81.6%compared with CK.The total N,total P and total K contents were the highest in rape-,corn-and rice straw biochar treatment,respectively,which increased by 74.8%,37.8%and 14.7%on average compared with CK.(3)The addition of three kinds of straw biomass chars changed the key enzyme activities of yellow soil fertility to varying degrees.Rice straw biochar had a better effect on catalase activity(CAT),and rape straw biochar had a better effect on urease activity(UAT)and neutral phosphatase activity(NPA)had a good improvement effect;Corn straw biochar had a good improvement effect on sucrase activity(SAT),which was 36.8-60.5%,37.6%～82.5%,13.5～47.9%and 51.5～96.0%higher than CK,respectively.In terms of the average effect of cultivation for two years,the addition of 4%was the best application rate for increasing CAT and NPA in yellow soil,and the addition rate of 2%was the best application rate for improving UAT and SAT in yellow soil.(4)According to the calculation of membership function:compared with CK,the comprehensive fertility index(IFI)of yellow soil was increased by 18.3%-185.3%by adding three kinds of straw biochar.The IFI values of different treatments the biggest to the smallest was as follows:T3(IFI 62.24)>T2(IFI 55.20)>T6(IFI 49.90)>T9(IFI43.83)>T1(IFI 40.83)>T5(IFI 38.07)>T8(IFI 31.71)>T4(IFI 28.26)>T7(IFI25.80)>CK(IFI).According to variance decomposition,the change of IFI in yellow soil was caused by the type of biochar and the amount of biochar added,their variance contribution rates were 41%and 56%,respectively,and the amount of biochar added had a greater impact on IFI in yellow soil.(5)A multiple linear regression model with IFI as response variable and fertility index as explanatory variable was established as follows:y=0.2602NPA+0.2518AK+0.2093SAT+0.1360SOM-0.0667TK+4.0654,R~2=0.98,P<0.0001.NPA had the greatest effect on IFI,followed by AK,SAT,SOM and TK.In conclusion,rape-,rice-and corn straw biochar were alkaline or strongly alkaline carboniferous products with obvious differences in physical and chemical properties.The IFI of yellow soil was improved by changed the soil fertility indexes(p H,SOM,AN,AP,AK,total N,total P,total K content,CAT,UAT,NPA and SAT)in the three kinds of straw biochar with different addition levels.The multiple linear regression model was established with NPA,AK,SAT,SOM and TK as explanatory variables and IFI as response variables had good fitting degree and could be used to predict and evaluate the effects of soil fertilizer cultivation under different treatments.The type and added amount of biochar were the key factors affecting the comprehensive fertility of yellow soil,and the rape straw biochar treatment with 4%addition level(T3)was the best treatment to improve the comprehensive fertility of yellow soil. |
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