Effects Of Different Origin Organic Materials On Active Carbon Pool In Mollisols Under Different Water Conditions

At present,the global extreme weather and climate events occurred frequently,the crop growing environment was accelerated worsened.To improve agricultural adaptation capacity is the main countermeasure to cope with climate change.Mollisols region is an important grain producing area in China.The climate changes accelerated the degradation of Mollisols and affected a serious threat to national food security.Soil active organic carbon is the most sensitive component of organic carbon,which is highly correlated with the internal productivity of soil,and is extremely sensitive to farming and environmental factors.Among them,particulate organic carbon?POC?is considered to be an important active organic carbon index reflecting soil carbon storage.Applying organic materials has always been the most important soil improvement measures.Therefore,we selected the four different origins organic materials to study on effects of that on active carbon pool?especially POC?in mollisols under different water conditions.We tried to discuss the role of POC in carbon sequestration,and hoped to identify the origin of organic materials that could improve mollisols to cope with rainfall change.This will offer a new angle to seek the soil improvement method to tackle climate change in a short term,and provide the theoretical foundation.After the 3-year field positioning and 5-year cultivating experiments,the following conclusions were reached:In crop growth season,under natural rainfall condition,leaves treatment was the best for water conservation and soil carbon storage,and the annual average growth rate of soil water content and SOC is 7.7%and 8.1%respectively;PMC of the stalks/leaves treatment was significantly lower than that of cow/chicken manure treatment.Long-term applying stalks/leaves greatly increased DOC and MBC with the annual average growth rate of above 70%;Cow/chicken manure treatment increased LFOC and POC with the annual average growth rate of above 15%.Under water deficit condition,the soil water content of chicken manure treatment showed an increasing trend,but the soil carbon storage of that was lower;the water conservation of cow manure treatment decreased,and the growth rate of DOC and MBC greatly decreased,but the carbon content of that increased;the organic carbon mineralization of stalks treatment greatly decreased,and the annual average growth rate of PMC was 13.4%,and it formed more LFOC and POC;leaves treatment formed more relative stable organic carbons.Under water excess condition,the soil water contents of organic materials treatments showed an increasing trend;the soil carbon storage of stalks treatment greatly decreased,but the organic carbon mineralization of that decreased slightly;the organic carbon mineralization of chicken manure treatment increased significantly,and the annual average growth rate of PMC was22.5%;LFOC and POC/SOC of cow manure/leaves treatment decreased significantly,and the potential capacity of soil carbon sequestration of that was better.In fallow season,under natural rainfall condition,organic materials improved water retention ability of mollisols and increased SOC;the loss of SOC of stalks/leaves treatment accelerated during freeze-thaw period with the annual average loss rate of about 4%;during freeze-thaw period,the loss of DOC,MBC,LFOC and POC of cow/chicken manure treatment all accelerated,but the organic carbon mineralization of cow manure treatment significantly increased,and the annual average growth rate of PMC was about 121%.Under water deficit condition,long-term applying chicken manure was the best for water conservation and soil carbon storage,and the organic carbon mineralization decreased,and the loss of DOC and MBC accelerated during freeze-thaw period,but the increase of LFOC accelerated,and the loss of POC slowed down.Under water excess condition,the water retention and SOC accumulation ability of cow manure treatment improved;the annual average decline rate of PMC was 17.7%during freeze-thaw period;the loss of LFOC of stalks treatment accelerated during freeze-thaw period,and POC/SOC of that increased,which showed an decreasing trend with the long-term applying stalks,but the decline rate of PMC was the lowest?8.9%?,so the soil carbon storage was less than other organic materials treatments.Organic materials improved the water retention as increasing the water content of deeper soil and inhibited the mineralization of organic carbon of deeper soil,and stored organic carbon into deeper soil,and then affected the vertical distribution of POC,especially POC/SOC.POC was mainly composed by alkyl and alkoxy carbons,the results of NMR analysis were similar to those of infrared spectroscopy.POC accumulated mainly as alkoxy carbon?POC content was significant and positive correlated with alkoxy carbon;r=0.478,p<0.05?,and degraded mainly from the degradation of carbonyl carbon,and its stability was mainly determined by the stability of fat carbons.Organic materials changed the molecular composition of POC in soil profiles,especially the contents of oxygen-containing functional groups and long-chain fatty carbon.Water conditions mainly affected the carbonyl carbon of POC,and organic materials mainly affected the alkoxy carbon and aromatic carbon of POC,and water excess promoted the formation of fat carbons of POC.Organic materials caused a positive priming effect on the inherent organic carbon to form POC in 20⁴0 cm layer.The increase of POC caused by cow/chicken manure was mainly in 0⁴0 cm soil layer that accounted for about 87%of 0⁶0 cm soil layer.Under water deficit condition,POC of chicken manure treatment become simpler,but POC/SOC of that decreased,and more relative stable organic carbons formed,and the depth of carbon sequestration reached 40 cm.Under water excess condition,cow manure treatment improved the activity of organic carbon in 20⁴0cm soil layer,which updated deeper soil organic carbon,but it also promoted the formation of complex long chain fat carbon of POC to increase the carbon accumulation above 40 cm soil layer.The increase of organic carbon came from decomposed stalks was mainly stored in 0²0 cm soil layer,but the inherent organic carbon was promoted to form POC under water conditions changes,and POC become simpler,especially under water excess condition.Leaves treatment promoted the formation of aromatic carbon and lessened effects of water changes on POC,and promoted the humification of POC in 20⁶0cm soil layer,especially in 40⁶0cm soil layer,which was beneficial to the organic carbon sequestration in deeper soil.Organic materials increased 100-gain weights and yields.Compared with natural rainfall,water deficit/excess significantly reduced maize yields,but organic materials slowed down the decrease of yields and ensured the quality of grains.Under natural rainfall,water deficit,water excess condition,the average increased yield was17.5%,37.2%and 15.9%respectively.But compared with the annual average yield of the control(14612 kg hm^-1)under natural rainfall,only leaves treatment(the annual average yield was 14640 kg hm^-1)guaranteed the yield under water deficit;under water excess,the yield of cow manure treatment increased 7.1%,and that of stalks/leaves treatment(14930 kg hm^-1;14475 kg hm^-1)was close to that of the control.PMC was significant and positive correlated with the 100-gain weight?r=0.108,p<0.01?,but it was significant and negative correlated with the yield?r=-0.204,p<0.01?.The correlation coefficient between POC and SOC?r=0.389?was bigger than that between LFOC and SOC?r=0.253?.So POC was more useful for evaluating organic carbon sequestration.LFOC was significant and positive correlated with the 100-gain weight or the yield?r=0.024,r=0.133;p<0.01?.So LFOC might be more useful for evaluating the quality and yield of the maize.In summary,taking guaranteeing the yield as the prerequisite,from the point of view of effects of carbon sequestration in deeper soil,the water adjustment ability of leaves treatment was the best;the flood resistance capability of cow manure treatment was better,but the drought resistance capability of that was poor;chicken manure treatment could store carbon under water deficit,but it could not guarantee the yield;stalks treatment could guarantee the yield under water excess,but its effect of carbon sequestration was relatively weak.