Changes In Crop Yield And Characteristics Of Soil Carbon Transformation Following Long-term Mulching Fertilization

Straw and film mulching have been widely used to improve crop yield in arid and semi-arid regions,yet comparative studies on their yield-increasing effects and their adaptability to different precipitation areas lack systematic studies,while the characteristics of soil carbon transformation under straw and film mulching and their transformation mechanisms are still incomplete.Therefore,crop yield response characteristics under straw and mulch were statistically explored in this study based on literature data;Based on the long-term mulch fertilization positioning trials[(fallow;no mulching,CT;straw mulching,（SM）;plastic film-mulched ridges and straw mulched-furrows,RF]started in 2003,we used a combination of soil level and agglomerate scale to elucidate the soil carbon transformation characteristics and its biological mechanism through carbon distribution,carbon transformation-related enzyme activities and functional gene analysis.The main conclusions are as follows:（1）Compared with CK,PM significantly increased crop yield in maize monocrop,wheat monocrop and wheat-corn rotation systems,SM showed the same trend but the yield difference between the two in maize monocrop system was not significant;Compared to SM,PM significantly increased crop yield in both wheat and maize monoculture systems,while the difference was not significant in wheat-maize crop rotation system.The PM to SM yield ratio(R_PM/SM)showed that mono-maize（1.28）>mono-wheat（1.11）>rotational maize（1.05）≈rotational wheat（1.04）.The regulating effect of reproductive precipitation（MSP）on R_PM/SMwas greater than that of annual precipitation（MAP）.R_PM/SM was stabilized at 1.082 and 1.001for MSP above 576 mm（mono-maize）and 500 mm（rotational maize）,respectively;The R_PM/SM was less than 1 when MSP exceeded 530 mm（mono-wheat）and 395 mm（rotational wheat）,respectively.R_PM/SM was less than 1 when the duration of mulching exceeded 10.3years（mono-maize）,14.6 years（maize rotation）and 16.7 years（wheat rotation）;R_PM/SM was stabilized at 1.075 when the duration of mulching exceeded 3.7 years（mono-wheat）.Compared with CK and PM,SM increased the effectiveness of SOC,TN,AK and MBC.Soil quality index（SQI）of SM>PM≈CK among mulching patterns in the monoculture system;SQI showed SM>PM>CK in the crop rotation system.MSP,soil moisture at sowing（SWC-S）,SOC and TN were important climatic and physicochemical variables regulating RPM/SM,independent of cropping system.（2）RF and SM significantly increased SWC,SOC,MBC,HE,FA,βG,CBH and Perox,while significantly decreasing soil bulk weight compared to CT.Compared with RF,SM significantly increased SOC,HA,αG,βG,CBH and Perox activities by 16.4%,12.8%,48.8%,156.9%and 195.1%,respectively;compared with fallow,CT significantly decreased p H but increased MBC,humus fraction andαG.（3）Compared to CT,RF had a significantly higher percentage of macroaggregates by 7.6%and a higher average weight diameter by 5.9%.Mulching increased the organic carbon content of macroaggregates,microaggregates and occluded microaggregates by 10.2%─17.5%,11.4%─17.5%and 10.2%─38.1%,respectively,and the effect of SM was greater than that of RF.Compared with Fallow,the proportion of macroaggregates in CT increased by 9.6%,the MWD increased by 9.0%,and the SOC in macroaggregates increased by 19.5%.Mulching significantly increased CBH activity in macroaggregates.The highest activity of carbon conversion related hydrolase in silt and clay（<0.053mm）,the highest activity of oxidase in microaggregates（0.053-0.25mm）.The effect of agglomerate size on SOC,MBC and enzymes activity was greater than that of mulching measures.Collectively,we can concluded that（1）long-term straw mulching has better agronomic benefits than mulching,（2）the influence of agglomerates on soil carbon turnover is more obvious than mulching measures,and（3）future research on the characteristics of agglomerate-scale carbon transformation under straw mulching should be strengthened.