| Low precipitation and less water use efficiency in rainfed areas of Longzhong are the main reasons for low and unstable crop productivity in the region.Implementation of tillage management is an effective means of sustaining the supply of soil and water and improving the water quality.To explore the mechanisms of conservation practices that affect water efficiency from a perspective of precipitation-soil water-crop water transformation(three related water),this study is based on the positioning test of longterm different tillage practices developed in 2001 in the dry farming area of the Loess Plateau;which has a total of 6 treatments,including conventional tillage;with no straw(T),no-till with straw cover(NTS),no-till with no straw cover(NT),conventional tillage with straw incorporated(TS),conventional tillage with plastic mulch(TP),notill with plastic mulch(NTP),spring wheat and peas rotation.The effects on the atmospheric-soil interface of different tillage practices,soil-crop interface,cropatmosphere interface water transformation and related factors were examined,and the mechanism for water transformation of crop water use efficiency affected by tillage practices was discussed,with the main findings as follows:(1)NTS and NTP improved productivity in spring wheat and field pea yield and water use.In contrast with T,NTS substantially increased dry matter accumulation before wheat flowering and before pea branching and podding,and NTP increased dry matter accumulation before wheat joining and pea branching.NTS and NTP increased the net photosynthetic output,increased the amount of spikes per area and spike wheat grains,pods per area and pea pod grains,and increased the coefficient of economy.The economic yield and WUE were higher in 2015-2016 with NTS,TP,and NTP than with T.The yield increases for spring wheat and pea in these three treatments were 19.61-45,8.08-31 and 20.39-41 percent respectively,and the WUE increases for spring wheat and pea were 10.30-36,5.65-14 and 18.35-25 percent respectively.(2)No tillage with straw cover improved soil physical characteristics,increased soil moisture content prior to sowing and improved soil water precipitation transformation performance.In comparison to T,NTS significantly increased the amount of stable mechanical aggregates,water-based aggregates and large particle size stability of > 0.25 mm,significantly reduced density of soil bulk,increased soil total porosity and improved soil saturated hydraulic conductivity.NTS significantly improved soil water retention capacity;under specific soil suction,NTS increased the soil mass water content by 16.80-23.20 percent.Before sowing,treatments with NTS and NTP improved soil water conservation considerably.NTS and NTP substantially improved the efficiency of storage of precipitation in both pea and wheat fields,with increases of 6.07-6.47% and 4.49-5.27% respectively.(3)NTS,TP and NTP enhanced roots' ability to retain water,increased soil water potential,reduced soil evaporation,increased crop transpiration,and improved the transition efficiency from soil water to crop water.Contrary to conventional straw-free tillage,NTS,TP and NTP improved root spatial distribution during flowering,and increased root dry weight,root length and root area of wheat and peas in multiple growth cycles;root dry weight increases were 11.15-79.04,23.24-66.81 and 37.99-157.93 percent respectively,root length increases were 8.61-90.79,12.83-46.50 and 12.09-89.36 percent respectively,and the increases of root surface were by 14.91-73.97,11.02-100.71 and 11.11-97.04 percent,respectively,thus,enhanced roots' ability to retain water.Compared to T,NTS significantly increased soil water potential at the level of wheat and pea seedling,and mulching treatments nearly increased soil water potential at soil depths of 0-30 cm at all growth stages of wheat and pea,and provided a complex basis for converting plant water into crop water.The transpiration rates increased by 81.69-117.60,41.14-97.36 and 57.83-87.17 percent respectively.NTS,TP,and NTP increased the dynamics of root water uptake.Total water consumption of NTS wheat and pea fields was slightly higher than that of T,while total water consumption of NTP was considerably higher only in wheat fields than in T.Meanwhile,NTS,TP,and NTP significantly decreased soil evaporation by 12.51-12.76,46.32-47.01,and 46.51-47.98 percent,respectively,27.95-36.78,46.35-58.79,and 48.79-77 increased crop transpiration,respectively,and increased the transition efficiency from soil water to crop water by 20.50-28.45,40.79-55.21 and 42.29-68.71,respectively.(4)Comprehensive factor of soil physical properties of 0-5cm(Spring wheat: r = 0.282,P > 0.05;Pea: r = 0.749,P < 0.01)and soil physical characteristics factor of 5-10cm(Spring wheat: r = 0.283,P > 0.05;Pea: r = 0.644,P < 0.01)was positively correlated with root synthesis factor,and root synthesis factor was significantly positively correlated with soil water potential synthesis factor(Spring wheat: r = 0.882,P < 0.01;Pea: r = 0.538,P < 0.05).Comprehensive factor of soil physical properties of 0-5cm(Spring wheat: r = 0.460,P < 0.05;Pea: r = 0.670,P < 0.01)and soil physical characteristics factor of 5-10cm(Spring wheat: r = 0.539,P < 0.05;Pea: r = 0.526,P < 0.05)was positively correlated with soil water storage before sowing.There was a significant positive correlation between soil water storage before sowing and the maximum precipitation storage efficiency(Spring wheat: r = 1.000,P < 0.01;Pea: r = 1.000,P < 0.01).Root synthesis factor was positively correlated with soil water-crop water transition efficiency(Spring wheat: r = 0.945,P < 0.01;Pea: r = 0.316,P > 0.05),the comprehensive factor of water potential was positively correlated with the transition efficiency from soil water to crop water(Spring wheat: r = 0.877,P < 0.01;Pea: r = 0.700,P < 0.01),the maximum precipitation storage efficiency was significantly positively correlated with the transition efficiency from soil water to crop water(Spring wheat: r = 0.556,P < 0.01;Pea: r = 0.408,P < 0.05),the transition efficiency from soil water to crop water and grain yield(Spring wheat: r = 0.502,P < 0.05;Pea: r = 0.521,P < 0.05)and grain yield water use efficiency(Spring wheat: r = 0.358,P >0.05;Pea: r = 0.521,P < 0.05)showed a significant positive correlation.To sum up,in Longzhong rainfed areas,no-till with straw cover and no-till with plastic mulch improved soil physical characteristics related to water transition,and improved the efficiency of precipitation transformation into soil water;At the same time,it fostered root growth,increased soil water potential,increased root system power to absorb water,decreased evaporation,and promoted water absorption and utilization in crops,improved soil water transformation efficiency into crop water.and thus improved yield and water use efficiency.Because no-till with straw cover is more sustainable than no-till with plastic mulch,so,no-till with straw cover is beneficial to the continuous improvement of water use efficiency of wheat and pea in Longzhong rainfed areas. |
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