| Tillage practices have a strong influence on soil organic carbon,soil structure and soil water use efficiency,as well as on sustainable agricultural development.Nevertheless,the changes in soil organic matter,soil structure,crop yield and water use efficiency under different tillage measures on the Loess Plateau remain unclear.A long-term field positioning experiment was carried out in this paper(started in 2007),and the conventional tillage(CT)measures was used as a control.The changes of soil organic carbon and its components,soil bulk density,aggregate stability,soil water storage,soil saturated hydraulic conductivity,photosynthetic rate,maize yield and soil water use efficiency under different tillage methods(single tillage practices i.e.,no-tillage(NT)and subsoiling(ST),rotational tillage practices i.e.,no-tillage/subsoiling(NS),subsoiling/conventional tillage(SC),conventional tillage/no-tillage(CN)),and the interactions between soil properties were studied.The aim was to identify the most appropriate tillage practices for the region to increase the soil carbon pool,improve soil structure and enhance soil productivity and crop yields.The main research results and progress are as follows:(1)The organic carbon stocks in the 0-40 cm soil layer of different tillage treatments were CN>SC>NS>CT>NT>ST.Compared to CT,the rotational tillage treatments such as NS,SC and CN increased by 9.51%,5.21% and 2.77%,respectively.In terms of soil organic carbon content and distribution,the rotational tillage treatments(NS,SC and CN)significantly increased soil organic carbon content in the lower layer(20-40 cm)compared to CT,while the no-tillage and subsoiling treatments(NT and ST)mainly increased soil organic carbon content in the surface layer(0-10 cm).The conventional tillage/no-tillage(CN)treatment showed the greatest increase in the particulate and mineral-bound organic carbon content,with increases of40.65% and 30.91% respectively compared to the ST treatment.The deeper(30-40 cm)soil polysaccharide,glucosamine and muramic acid contents were significantly increased by the rotational tillage treatments compared to the CT treatment.Among them,the greatest increase was also observed under the CN treatment,with significant increases of 59.75%,37.39% and64.87% respectively.(2)Total soil porosity and aeration porosity were significantly increased and soil bulk density and inactive porosity were reduced under the rotational tillage treatments.Compared to CT,the no-tillage/subsoiling(NS)treatment increased total soil porosity,aeration porosity and capillary porosity by 17.83%,47.00% and 22.89%,respectively,and significantly reduced soil bulk and inactive porosity by 17.08% and 20.24%,respectively.In the 0-30 cm soil layer,the NS and conventional tillage/no-tillage(CN)treatments significantly increased the >2 mm aggregate content,and subsoiling/conventional tillage(SC)significantly increased the 2-0.25 mm aggregate content.The SC and NT treatments significantly increased the stability and mean weight diameter of the 0-40 cm soil aggregates and reduced the fractal dimension compared to the CT treatment.(3)The soil saturated hydraulic conductivity increased by 32.03%,19.99% and 25.11% in the rotational tillage treatments(NS,SC and CN)compared to CT,respectively.Notillage/subsoiling(NS)and conventional tillage/no-tillage(CN)treatments increased field capacity by 4.12% and 2.12% respectively compared to CT.NS treatment increased soil water storage during the fallow period of spring maize by 19.62 mm compared to CT.NT treatment had the highest soil water storage capacity of 430.30-400.21 mm throughout spring maize.The NS,SC and CN treatments increased soil water use efficiency by 32.06%,18.56% and 37.97%respectively compared to CT.NS and CN treatments increased the chlorophyll content and photosynthetic rate of maize and reduced the transpiration rate of maize,thus significantly increasing the final yield of maize.(4)Correlation analysis showed a significant correlation between soil organic matter,soil structure and water.Soil field capacity and saturated hydraulic conductivity were significantly positively correlated with soil organic carbon and its components(particulate organic carbon,mineral-bound organic carbon,soil polysaccharides,glucosamine,muramic acid)and active pore space(capillary porosity and aeration porosity).In addition,soil water storage was only highly significantly positively correlated with soil structural stability and mean weight diameter,and highly significantly negatively correlated with fractal dimension.Combined with the redundancy analysis,soil organic carbon,muramic acid and saturated hydraulic conductivity were found to be the main factors affecting photosynthetic effects,yield and soil water use efficiency in maize.No-tillage/subsoiling and conventional tillage/no-tillage could increase the accumulation of bacterial residues,improve soil water-holding properties and regulate soil pore structure,which in turn had a positive effect on maize photosynthetic effect,yield and soil water use efficiency.In summary,rotational tillage measures reduced soil bulk density in the deep layer(20-40cm),and increased soil organic matter,soil aggregates stability,and enhance soil aeration and permeability.Compared with conventional tillage,no-tillage/subsoiling and conventional tillage/no-tillage treatments were more effective in improving soil fertility,soil structural stability and water holding capacity,promoting crop growth and development,and increasing maize yield and soil water use efficiency.Therefore,to simultaneously achieve the objectives of increasing soil fertility,improving soil structure,and increasing grain yield and water use efficiency,no-tillage/subsoiling and conventional tillage/no-tillage in combination with rotational tillage measures are the optimal tillage methods for semi-arid loess plateau areas. |
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