Effect Of Combined Application Of Straw And Desulfurized Gypsum On Organic Carbon Sequestration In Coastal Saline-alkali Soil

Soil salinity and low fertility are the main"bottlenecks"restricting factors for the efficient development of coastal saline agriculture.The current research focus is how to improve soil organic carbon（SOC）,fertilize,and soil quality.Industrial and agricultural waste-straw and desulfurized gypsum have significantly reduced salinity barriers.At present,there are many researches on the effect of single straw or desulfurized gypsum on the improvement and fertilizer cultivation of saline-alkali soil at home and abroad.Studies on compound amelioration mainly focus on the effect of alkali reduction and salt removal in inland saline-alkali soils,while there are few studies on the effect of organic carbon sequestration in saline-alkali soils in the Yellow River Delta.Here,we carried out laboratory incubation and field experiments with the Yellow River Delta saline alkaline soil to assess the responses of organic carbon mineralization,different organic carbon content,soil agglomeration and physical and chemical properties under the straw combined with desulfurization gypsum.Meanwhile,through clarifying the key factors affecting soil organic carbon sequestration,we hope to provide scientific basis for optimizing carbon sequestration strategy of saline-alkali soil in the Yellow River Delta and rationally utilizing industrial and agricultural wastes to improve and fertilize saline-alkali soil.The main conclusions are as follows:（1）Soil carbon mineralization can be increased either with straw alone or with desulfurized gypsum.The cumulative release of CO₂-C in straw combined with desulfurized gypsum treatment was lower than that in straw alone treatment.Under the same amount of straw,the cumulative release of CO₂-C decreased with the increase of the amount of desulfurized gypsum.（2）Soil dissolved organic carbon（DOC）,microbial biomass carbon（MBC）,and soil microbial entropy showed an overall upward trend with the increase of straw addition.The treatment of desulfurization gypsum+medium straw（GMS）and desulfurization gypsum+high straw（GHS）was significantly higher than that of single straw（MS）.Straw combined with desulfurized gypsum（GLS、GMS、GHS）treatments not only significantly increased the content of new carbon(C_new)from straw compared with MS treatment,but also maintained the content of soil original organic carbon(C_old)at a level similar to MS treatment.（3）The proportion of macro-aggregates（>0.25 mm）,average weight diameter（MWD）and R_0.25of straw with desulfurized gypsum treatment were significantly higher than those of desulfurization gypsum（GD）and MS treatment,The content of organic carbon and new carbon in the aggregate increases with the increase of particle size.The organic carbon content of macro-aggregates was significantly increased by straw alone or straw combined with desulfurization gypsum.At the same time,the contribution rate of 0.25-2 mm aggregates under straw combined with desulfurized gypsum treatment was significantly higher than that of GD and MS treatment,The new carbon content of macro-aggregates treated by GMS and GHS was significantly higher than that in the MS treatment.（4）Both MS and GHS significantly reduced soil bulk density and increased soil total porosity and soil moisture content.Straw combined with desulfurization gypsum（GLS、GMS、GHS）treatments significantly reduced Na⁺and Cl^-,and increased Ca²⁺and SO₄^2-,and the effect was better than GD and MS treatments.Meanwhile,the sodium adsorption ratio（SAR）of this treatment was significantly lower than that of MS.Correlation study showed that MWD was negatively correlated with Na⁺,but positively correlated with DOC,SOC,C_newand 0.25-2 mm aggregate organic carbon and new carbon content,SAR and ESP were negatively correlated with MBC,C_new and>2 mm aggregate organic carbon.In addition,the redundancy analysis also showed that soil MWD,ESP,SAR and Na⁺were the main factors affecting soil carbon sequestration.In conclusion,compared with single measure,straw combined with desulfurization gypsum increased soil carbon content and enhanced soil carbon sequestration potential.And it is beneficial to reduce the soil sodium level,the soil alkalinity,improve the stability of aggregates,and then realize the soil carbon enrichment and fertilizer conservation.