Meta-analysis Of Effects Of Biochar Application On Soil Nitrogen And Plant Growth

Biochar can improve soil physical and chemical properties,regulate soil nitrogen content,maintain fertilizer and increase yield,but its role is affected by many external factors,such as soil texture,acidity and alkalinity,initial soil nutrient status,soil fertilization,crop types,physical and chemical properties of biochar itself,and its influence law is not clear.Metaanalysis is a kind of statistical method that comprehensively analyzes many research results of the same subject with specific conditions.It can judge whether different influencing factors will have positive or negative effects on the experimental object and the size of the effects,and its analysis results are more comprehensive.Therefore,based on the scientific theory of metaanalysis method,this study collected the articles on biochar and soil nitrogen,crop nutrient absorption and crop yield published on web of Science in recent 20 years from 2000 to 2020(190 articles were obtained and 18035 groups of observation data were extracted),quantitatively analyzed the impact of biochar on Soil nitrogen,crop nutrient absorption and yield,and identified different crop types The effects of biochar application amount,biochar production raw materials,soil texture and soil pH on biochar effect.The test results show that:(1)As for soil nitrogen,on the whole,the effect of biochar on soil total nitrogen content is significantly affected by test type,crop type,biochar application amount,pyrolysis temperature,production raw materials,biochar C/N,carbon content,soil pH,organic carbon content,total nitrogen content and fertilization type;The effect of biochar on soil ammonium nitrogen content was significantly affected by test type,test years,biochar application amount,pyrolysis temperature,biochar C/N,specific surface area,soil texture,organic carbon content and total nitrogen content;The effect of biochar on soil nitrate content was significantly affected by crop type,annual rainfall,biochar pH,soil pH and total nitrogen content;The effect of biochar on soil microbial biomass nitrogen content was significantly affected by crop type,biochar C/N,specific surface area,biochar carbon content,soil texture,organic carbon content and total nitrogen content.(2)In different crop types,biochar had the greatest effect on the increase of total nitrogen content in the soil planted with chickpea,nitrate nitrogen content in the soil planted with barley and microbial biomass nitrogen in the soil planted with rice;Among the different application rates of biochar,when the application rate of biochar is >40 t/ha,it has a significant positive effect on the content of total nitrogen in soil,with an increase rate of 39.6%,while it has a significant negative effect on ammonium nitrogen,reducing the content of ammonium nitrogen by 28.2%;Among different pyrolysis temperatures of biochar,biochar produced at >600℃ has the least effect on the increase of total nitrogen content,with an increase rate of 4.7%,and also significantly reduces the content of ammonium nitrogen in soil,with a decrease of 28.8%.Biochar produced at pyrolysis temperature ≤400℃ has the greatest effect on the increase of total nitrogen content,and can also significantly increase the content of ammonium nitrogen in soil,with an increase rate of 32.8% and 13.7% respectively;Among the initial organic carbon content of different tested soils,when the organic carbon content is ≤5 g/kg,biochar has a significant increase effect on total nitrogen,ammonium nitrogen and microbial biomass nitrogen in soil,which is significantly higher than other content ranges,and the increase rates are 61.2%,11.3% and 44.5% respectively;In the initial total nitrogen content of different tested soils,when the total nitrogen content is ≤ 0.5 g/kg,biochar has a significant increase effect on total nitrogen,ammonium nitrogen and microbial biomass nitrogen in the soil,which is significantly higher than other content ranges,and the increase rates are 53.9%,10.7% and 74.4%respectively.(3)On the whole,the effect of biochar on crop nitrogen uptake was significantly affected by biochar pH and soil organic carbon content;The effect of biochar on crop yield was significantly affected by the test type,average annual rainfall,raw materials for biochar production,carbon content,soil pH,organic carbon content and total nitrogen content;The effect of biochar on stem and leaf biomass was significantly affected by test type,test years,crop type,biochar application amount,biochar C/N and soil pH;The effect of biochar on crop root biomass was significantly affected by the pyrolysis temperature of biochar.(4)Among different biochar pH and soil organic carbon content,when pH≤7 and organic carbon content ≤5 g/kg,biochar had the greatest increasing effect on crop grain nitrogen absorption,and the increasing rates were 22.5% and 22.4% respectively;In different experimental types,the application of biochar had the greatest yield increase effect in the culture experiment,and the grain yield and stem and leaf biomass increased by 19.0% and 23.7%respectively;In different soil pH,when pH≤5.5,the yield increasing effect of biochar was the largest,and the grain yield and stem and leaf biomass increased by 30.2% and 97.9%respectively;Biochar produced at pyrolysis temperature ≤400℃ had the greatest effect on the increase of crop root biomass.