| The Weibei dryland region,located in the south of the Loess Plateau,serves as an important traditional rainfed agricultural region in China,in which continuous winter wheat is the most important cropping system.However,the distribution of precipitation season and winter wheat growing season was inconsistent,which resulted in low and unstable wheat grain yield.In addition,the management method of conventional plowing with harrowing during the fallow period has long prevailed in this area,it is easy to damage the soil structure,causing soil surface exposure,accelerating the soil organic carbon decomposition and soil moisture evaporation,thus resulting in the decline of arable land quality,which seriously restricts the quality of agricultural development in the Weibei region.Therefore,how to construct cropping systems and tillage practices suitable for local natural conditions,increase soil carbon fixation capacity,and improve soil fertility and crop productivity become urgent issues to be solved in the process of high-quality agricultural development in Weibei dryland region.Therefore,this study is based on the long-term successive field study in Heyang in the Weibei dryland region,which has been implemented in 2007.According to the two factor split-plot experimental design method,three cropping systems are used as the main treatment(continuous winter wheat(WWC),continuous spring maize(SMC),and rotation of winter wheat-spring maize(WMR)),and five tillage practices are used as the sub treatment(NT,no tillage;ST,subsoiling tillage;CT,conventional tillage,rotation of ST and CT(SC),rotation of NT and CT(CN))was used to conducted to study the effects of different tillage practices on soil structure,soil organic carbon sequestration,soil water storage,and crop yield for wheat-maize rotation or continuous cropping fields in weibei region.The main results are as follows:(1)The content of macroaggregates in dryland fields showed an increasing trend compared with the initial stage of the experiment,while soil bulk density and porosity varied with changes in tillage practices during the fallow period.After successive cultivated 14 years,the effects of cropping systems and tillage practices on soil bulk density,porosity,and aggregate composition in dryland fields reached a significant level(P<0.05).Compared with continuous winter wheat,rotation of winter wheat-spring maize and continuous spring maize increased soil bulk density by 0.8% and 2.2%,respectively,and the soil porosity decreased by0.7% and 2.5%,respectively.Rotation of winter wheat-spring maize increased the content of soil macroaggregates and the mean weight diameter of aggregates,resulting in a more stable soil aggregate structure.The effects of tillage practices on soil structural characteristics varied in different soil layers.Compared with conventional tillage(CT),conservation tillage(NT and ST)increased soil bulk density in the surface soil layer(0-20 cm)and decreased soil macroaggregate content in the 20-40 cm soil layer;Rotational tillage(SC and CN)increased the bulk density of the surface layer(0-20 cm soil layer),but also increased the soil porosity and mass proportion of soil macroaggregates of 20-40 cm soil layer,improved the soil structure,and increased the permeability.(2)The soil organic carbon content in dryland grain fields showed an increasing trend compared with the initial stage of the experiment,and the increase rate was the largest under conservation tillage(NT and ST).After successive cultivated 14 years,the effects of cropping systems and tillage practices on soil organic carbon,aggregate organic carbon,and aggregate organic carbon contribution rates in dryland fields reached a significant level(P<0.05).Compared with continuous winter wheat,rotation of winter wheat-spring maize and continuous spring maize significantly increased soil organic carbon content and aggregate related organic carbon content,which was mainly related to the higher inputs of crop residue carbon under these two cropping systems,among which the amount of crop residue carbon inputs under rotation of winter wheat-spring maize and continuous spring maize was 78.3%and 175.9% higher than that under continuous winter wheat,respectively(P<0.05).In addition,the rotation of winter wheat-spring maize significantly increased the diversity of soil microorganisms involved in the carbon cycle(P<0.05),as well as the gene abundance of carbohydrate active enzyme family encoding lignin,chitin,and glucan,reducing the abundance of genes encoding hemicellulose and cellulase.Compared with CT,conservation tillage(NT and ST)increased the soil organic carbon content and aggregate related organic carbon content in the surface layer(0-20 cm soil layer),especially the fine particle organic carbon content in macroaggregates and microaggregates,but decreased the soil organic carbon content in 20-40 cm soil layer;Rotational tillage(SC and CN)reduced the organic carbon content of the surface soil layer compared to conservation tillage(NT and ST),but increased the organic carbon content in the 20-40 cm soil layer.(3)The soil water conservation rate during the fallow period in dryland fields varies with the change of precipitation during the fallow period,and the soil water conservation rate in continuous winter wheat field during the fallow period is significantly higher than that in rotation of winter wheat-spring maize and continuous spring maize fields(P<0.05).The distribution characteristics of soil water profile during the growth period are different under different cropping systems.The soil water consumption in the continuous winter wheat exceeded 200 cm of soil layer,and formed a dry soil layer in the 120-280 cm soil layer.However,the phenomenon of excessive soil water consumption in the rotation of winter wheat-spring maize only occurs in the winter wheat season.The effect of cropping systems on soil moisture in the deep layer(0-500 cm soil layer)reached a significant level(P<0.05).Compared with continuous winter wheat,soil water storage in rotation of winter wheat-spring maize and continuous spring maize increased by 10.8% and 21.6%,but the effect of tillage practices on soil moisture in the deep layer was not significant.Linear fitting analysis showed that there was a significant positive correlation between soil organic carbon and macroaggregates and soil water conservation rate during the fallow period,and structural equation model analysis showed that the impact of soil organic carbon on soil moisture mainly occurred indirectly through its impact on soil structure.(4)Crop roots in dryland fields are mainly distributed in the 0-20 cm soil layer.Winter wheat roots can extend to the 200 cm soil layer,but spring maize roots only extend to 160 cm soil layer.The effects of cropping systems on the root length density and root surface area density of 0-200 cm soil layer in dryland fields were significant(P<0.05).In the 0-40 cm soil layer,the root length density and root surface area density of winter wheat were significantly lower than those of spring maize,but in the 40-200 cm soil layer,winter wheat was significantly higher than spring maize.The effect of tillage practices on root length density is mainly occurred in the 0-40 cm soil layer.Compared with CT treatment,NT significantly reduces root length density(17.9% and 4.6% lower on and between rows,respectively),while rotational tillage practices increased maize root length density and promoted the root extend to deeper soil layers.Linear fitting analysis showed that there was a significant positive correlation between crop root length density and soil porosity,macroaggregate content,and organic carbon storage,while there was a significant negative correlation between soil water storage.(5)Grain yield and water use efficiency,as well as economic benefits fluctuate with changes of precipitation during the growth period under long-term different tillage practices in dryland fields.The effects of cropping systems and tillage practices on grain yield,water use efficiency,and economic benefits reached a significant level(P<0.05).Compared with continuous winter wheat,rotation of winter wheat-spring maize and continuous spring maize significantly increased grain yield,water use efficiency,and economic benefits.Grain yield increased by 33.4% and 55.2%,water use efficiency increased by 36.2% and 52.7%,and economic benefits increased by 42.6% and 63.5%,respectively.However,rotation of winter wheat-spring maize did not improve the yield stability and sustainability.Compared to longterm single tillage(NT,ST,and CT),rotational tillage(SC and CN)achieves the highest grain yield and economic benefits,and also improving water use efficiency,which is related to the higher total dry matter accumulation and the contribution rate of dry matter to grain yield after flowering under rotational tillage.In summary,rotation of winter wheat-spring maize,combined with rotational tillage practices can effectively improves soil structure,promotes soil carbon sequestration,enhances soil water conservation,and further promotes crop growth and development.A good soil environment also promotes the absorption and utilization of soil water by crop roots,thereby improving crop yield,water use efficiency,and economic benefits.Therefore,cropping system should focus on the rotation of winter wheat-spring maize on the basis of taking into account the balance between supply and demand of grain and forage in the Weibei dryland region.The appropriate tillage practices to improve the productivity of arable land should be based on conservation tillage practices,achieving the synergistic enhancement of soil carbon sequestration and soil water conservation,and adding conventional tillage to the conservation tillage practices,to adjust the soil structure and soil water and fertilizer distribution,and provide a good soil environment for crop growth,thereby achieving the goal of increasing production and income. |
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