Biochar Effects On Soil Quality,Crop Production And Greenhouse Gas Emission From A Rice Paddy Under Rice And Wheat Rotation:Role Of Water Extractable Pool

Food production is one of society's key sensitivities to climate.While modern farming technologies and techniques have helped to reduce agricultural weakness and boost production,the impact of recent droughts in the USA,China and Russia on global cereal production highlight a glaring potential future weakness.Land degradation manifested as heavy metal contamination of agricultural and urban soils,loss of organic matter leading to poor soil structure,compaction,and loss of soil fertility all contribute to low agricultural productivity.Use of biochar from bio-wastes has been proposed as an option to improve soil fertility,restore degraded lands,and mitigate greenhouse gas emissions in global agriculture.Over the past 10 years,there have been hundreds of research studies on biochar from which it may be possible to determine appropriate methods for use of biochar to improve sustainable agriculture.Biochar generally contains a major portion of recalcitrant fraction and a small but significant pool of labile C fraction.However,there had been yet not enough studies addressing the role of this small labile C pool in soil quality,crop productivity and greenhouse gas emission from biochar amended agricultural soils.The objectives of this study therefore were,to quantitatively examine the effect size of extracted biochar on soil physical and chemical properties,crop performance,micro-nutrient availability,soil respiration and greenhouse gas emission in biochar amended rice paddy,and to identify the main factors that influence the response of soil physical and chemical properties,crop performance,micro-nutrient availability,soil respiration and greenhouse gas emission unextracted and extracted biochar amendment.To achieve our objectives,we employed a field experiment over two rice-wheat rotation seasons following a single amendment to a rice paddy.Two different types of biochars(maize straw biochar and wheat straw biochar)both of water extracted and unextracted were respectively amended at 20 t·ha-1 to a rice paddy under rice wheat rotation from the Tai Lake plain,China.The application rates at the range of 10 to 20 ha-1 seem feasible.However,as we got indication of even yield reductions in fertile soils,we recommend that farmers start experimenting with care,and target the least productive parcels to gain experience.The study was divided in three parts.Biochar has been increasingly recommended for improving soil fertility and availability of micro-nutrients.This study aimed to examine changes in soil physico-chemical properties and micro-nutrients availability under soil amendment of unextracted and extracted biochar's.Two different types of biochars(maize straw biochar and wheat straw biochar)both of unextracted and extracted were respectively amended at 20 t·ha-1 to a rice paddy under rice wheat rotation from the Tai Lake plain,China.Soil physico-chemical properties and micro-nutrients availability analyzed throughout the crop growing seasons during 2015-2016.Unextracted biochar's treatment increased available P,K,Fe,Mn,Cu and Zn as compared to extracted biochar's treatment.There was no difference in changes in soil bulk density and total nitrogen between the two biochars and between unextracted and extracted biochars,regardless of crop seasons.Therefore,water extraction of biochar did affect biochar performance on soil fertility and micro-nutrients availability for the first rice seasons.The application of unextracted biochar could be preferred to improve soil fertility and micro-nutrients availability.The second part of the study aimed to examine changes in crop performance,grain yield and root morphology under soil amendment of unextracted and extracted biochar's.Two types of biochars(maize straw biochar and wheat straw biochar)both of water extracted and unextracted were respectively amended at 20 t·ha-1 to a rice paddy under rice wheat rotation from the Tai Lake plain,China.Plant traits,crop yield and root morphology analyzed throughout the crop growing seasons during 2015-2016.For the first crop season of rice,the increase in grain yield was higher under unextracted than under extracted maize or wheat biochar.This was in line with the increase in LAI ratio,root volume,average root diameter,total root length per volume and thousand grain weight for rice season.However,there were hardly differences in grain yield,LAI and TGW for the subsequent wheat season.With respect to nutrient uptake,unextracted and extracted biochar increased the absorption of nitrogen in rice and wheat grain and straw.However,there was no significant difference between the unextracted and extracted biochar treaments.In addition,the unextracted and extracted biochar enhance phosphorous and potassium in grain and straw uptake rice and wheat crop growing season.Therefore,extracted biochar did affect biochar performance on crop growth and grain yield for the rice-wheat growing seasons.The application of unextracted biochar could be preferred to improve soil fertility and crop productivity from rice paddy under the rice wheat rotation.The third study explored the temporal increases in soil respiration and thus a priming effect on soil organic carbon decomposition have been often argued owing to the existence of a small extractable carbon pool.This study aimed to examine changes in soil respiration and greenhouse gas emission under soil amendment of unextracted and extracted biochar.Two types of biochars(maize straw biochar and wheat straw biochar)both of unextracted and extracted were respectively amended at 20 t·ha-1 to a rice paddy under rice wheat rotation from the Tai Lake plain,China.Soil greenhouse gas emissions were monitored throughout the crop growing seasons during 2015-2016.The increase in soil organic carbon(SOC)was no difference between two biochars but higher under unextracted than under extracted wheat biochar.There was no difference in changes in microbial biomass carbon between the two biochars and between unextracted and extracted biochars,regardless of crop seasons.Generally,there was no difference in soil GHG emission and thus GHGI changes between unextracted and extracted biochar regardless of biochar types and crop seasons.Of course,for submerged rice soil,methane emission was lower under extracted maize or wheat biochar.Therefore,water extraction of biochar did not affect biochar performance on soil respiration and GHG emissions despite of a reduction of methane emission for the first rice seasons.Thus,a small change due to extraction in water extractable carbon pool was not seem responsible for a soil respiration increase and thus a priming effect with biochar amendment in rice season.This study provides the evidence that a small pool of extractable C does not affect soil respiration,ecosystem greenhouse gas emission and microbial biomass.The changes in the responses of soil physical and chemical properties and crop performance to extracted or unextracted biochar varies with feedstock source,pyrolysis temperature and application rates.The greenhouse gas emission mitigation and microbial biomass carbon changes were however shown to be initially high but non-significant.The mechanism for reducing greenhouse emission and promoting microbial biomass remain unclear.There is therefore an urgent need for long-term experiments to determine the biochar aging effects on soil respiration and greenhouse gas emission.