Effect Of Straw Mulching On Soil Ecological Properties And Crop Production In A Dryland Winter Wheat Field

As one of the most important dryland agricultural area,the Loess Plateau is characteristiced with lack of precipitation and low soil fertilities.In the recent decades,straw mulching has widely been adopted due to its effect of conserving soil water,controlling soil temperature and increasing organic matter input in this area.However,the long term effect of straw mulching on soil properties and crop production is still not well known in the Loess Plateau.In the study,based on a 10-yr field experiment,the responses of soil carbon and nitrogen sequestration,soil aggregation,greenhouse gas?CO₂,CH₄,N₂O?flux,soil microbial community,and crop biomass and yield to straw mulching were measured under winter wheat systematically.Four treatments were included as no mulching?CK?,high straw mulching at a rate of 9000 kg hm^-22 during growing season?HSM?,low straw mulching at a rate of 4500 kg hm^-22 during growing season?LSM?and straw mulching at a rate of 9000 kg hm^-22 during summer fallow season?FSM?.The main results are as follows:?1?Compared with CK,soil water storage at wheat planting at 0-200 cm with HSM, LSM and FSM were increased by 3.74-6.03%when averaged across years.Compared with CK,straw mulching could increase precipitation-storage efficiency,by 7.91-16.6%,and the effect is more obvious in dry years.The straw mulching during summer fallow is more conducive to improve the precipitation-storage efficiency than straw mulching during the growing season.Straw mulching also changed the water consumption pattern of winter wheat.There was no significant difference in soil water in the early growing season among different treatments,but straw mulching could increase soil water consumption in the late growing season of winter wheat.Compared with CK and FSM,HSM and LSM increased the daytime soil temperature at 0-25 cm during most growing stages,and decreased the maximum daytime soil temperature,indicating that straw mulching could stabilize the fluctuation of soil daily temperature during wheat growing season.Compared with CK,HSM and LSM had a significant“cooling effects”on the average daily temperature at surface soil in the early growing stages of winter wheat,while FSM had little effect on the soil temperature.?2?Averaged across years,straw mulching increased the contents of SOC,POC,PCM and MBC at 0-20 cm soil depth significantly compared with CK.All C fractions at 0-20cm were 4.20%-39.4%greater with straw mulching than CK,and the increasing effect of straw mulching was more significant during growing season than summer fallow.Soil C sequestration and microbial biomass and activity was greater with HSM and LSM than CK and FSM,and greater with HSM than LSM.Averaged across years,HSM and LSM increased the STN content by 8.05%and 6.61%,the MBN content by 16.3%and 14.5%compared with CK,respectively.The MBN content was greater by 16.6%,22.3%and36.8%with HSM than CK,LSM and FSM,respectively.The effects of straw mulching on soil carbon and nitrogen fractions varied with years.At the 0-20 cm soil depth,POC,PCM,STN,MBN and MBN/STN were significantly positively correlated with the estimated wheat root residue returned to the soil.Overall,straw mulching was beneficial for soil carbon and nitrogen,and such effect was better during growing season than during summer fallow.?3?Straw mulching could promote the formation of mechanical aggregation and its stability,and the influence was more significant during growing season than during summer fallow.Compared with CK and FSM,HSM and LSM increased the carbon fractions in most aggregate sizes,and the difference of SOC in aggregates between HSM and LSM is not significant.The increasing effect of straw mulching on soil carbon fractions in soil aggregates mainly occurred at 0-10 cm.The effect of straw mulching on the nitrogen fraction was only found in certain aggregate size.Soil carbon and nitrogen fractions were mainly stored in the macroaggregates,and the contribution rate of carbon and nitrogen fraction in macroaggregate size was over 75%.Straw mulching increased the contribution rate of SOC,PCM,MBC,STN,PNM and MBN in macroaggregate at 0-10cm,and such effect was more significant with HSM than LSM and FSM.?4?Soil greenhouse gas emission was measured dynamically in 2017-2018.Compared with CK and FSM,HSM and LSM reduced the CO₂ cumulative emission flux during the growing season,and the CO₂ cumulative emission flux was lower with HSM than LSM.FSM increased the N₂O and CH₄ cumulative emission fluxes during the summer fallow season when compared with CK.Soil CO₂ and N₂O emission fluxes were positively correlated with soil temperature and water content.Soil CH₄ emission flux decreased and then increased with the increasing temperature.Soil CH₄ emission flux was positively correlated with soil water content.Compared with CK,both HSM and LSM decreased the global warming potential,while FSM had no significant impact on the global warming potential in the dryland wheat monocultural systems.?5?Straw mulching changed soil microbial diversity and community composition,and the community structure of HSM was significantly different from that of LSM and FSM at 0-20 cm.Bacterial Shannon index was greater with HSM,LSM and FSM than CK,but the fungal Shannon index was lower with HSM than FSM.At 0-20 cm soil depth,HSM,LSM and FSM increased the relative abundance of Proteobacteria,by 23.3%,47.0%and 46.0%and decreased the relative abundance of Actinobacteria,by 16.7%,51.2%and 46.0%when compared with CK,respectively?P<0.05?.The relative abundance of Acidobacteria was also increased with straw mulching.No significant difference in the relative abundance of Ascomycota was found among different treatments.The activity of?-Glucosidase,Cellobiohydrolase and Xylosidase were increased with straw mulching,and was higher with FSM than HSM and LSM.Most of carbon and nitrogen fractionsexcept of PNM,soil moisture,and the activity of?-Glucosidase,Alkaline phosphatase,Acetylglucosidase and Xylosidase were positively correlated with phyla Proteobacteria,Acidobacteria,Nitrospirae,Planctomycetes and Bacteroidetes,and negatively correlated with phylum Acidobacteria,respectively.Overally,soil microbial community structure and diversity were significantly affected by the changes in soil carbon and nitrogen fractions and physical and chemical properties that caused by straw mulching.?6?Winter wheat yield,1000-grain weight and harvest index,and HSM were lower with HSM and LSM than CK and FSM,and HSM than LSM.FSM increased wheat stem number,spike number,tiller number and 1000-grain weight,but had no significant effect on grain yield and aboveground biomass compared with CK.Crop yield and its components varied with years.In the rainy years,straw mulching decreased crop yield and water use efficiency in the rainy years,while the increasing impact of straw mulching on crop production was only found in the dry years.The maximum tilling rates of winter wheat was delayed by 2 days with HSM,which would lead to the reduction in grain yield in the rainy years.Straw mulching could increase soil water storage and precipitation-storage efficiency,but was not conducive to improving winter wheat water use efficiency.The average daily temperature at seedling-tillering stage was lower with HSM and LSM than CK and FSM,which decreased the number of winter wheat seedlings.Wheat yield was significantly correlated with PCM and PNM,indicating that the enhancement of straw mulching on soil microbial activity would have a positive influence on crop production.In addition,straw mulching increased soil carbon and nitrogen content in the surface soil depths,but straw mulching during growing season decreased soil mineral nitrogen levels after the wheat returning green stage,which might limit the transformation of drymatter into grains during the maturation stage.