| Intercropping has been widely applied in the arid and semi-arid regions because of high or stable productivity and the efficient utilization of resources.In recent years,the application of intercropping was faced great challenges because the serious shortage of water resources.It needs to be further researched urgently in the theory and technology of water-saving in intercropping.Interspecies relationship is an important basis for determining the efficient use of water in the intercropping sytem.To further improve the water use efficiency,regulate the relationship between interspecies competition and facilitation via optimizing cultivation measures,and make full use of spatial-temporal niche differentiation is current scientific problem to be urgently solved.In this study,a field experiment was carried out in typical oasis irrigation region,in order to investigate the effect of straw retention and plastic film mulching patterns on water competition and complementary utilization in wheat-maize intercropping system,to reveal the basic mechanism of alternate strip mulching with straw and plastic film regulated the grain yield and water use efficiency of intercropping.It also provided theoretical and technical basis for improve water utilization via coordinating interspecies competition and complementarity in the intercropping.The main results are follows:1.Intercropping had the advantages on maintaining high soil water potential in comparison with monoculture.Alternate strip mulching with straw and plastic film decreased the difference value on soil water potential during the co-growth stage,and increased the difference value on soil water potential after wheat harvest,between the two crop strips,which formed the hydrodynamics basis for water competition and complementary utilization at spatial and temporal niche.During the wheat independent growth period,the averaged soil water potential of intercropped maize strips was greater 11.7 to 17.5% than that of wheat strips,and the soil water potential of intercropped maize strip was greater 9.2 to 13.6% than that of wheat strip under the treatment on no-tillage and straw covering in wheat strip combined with two-year plastic film mulching in maize strip(i.e.,NTSI2);also,the soil water potential of intercropped maize strip was greater 14.1 to 22.7% than that of wheat strip under the treatment on deep tillage without straw residue retention in wheat strip combined with every-year new plastic film mulching in maize strip(i.e.,CTI,conventional intercropping treatment).Across wheat-maize co-growth period,the averaged soil water potential of intercropped maize strips was greater 18.0 to 20.7% than that of wheat strips;the soil water potential of intercropped maize strip was greater 15.7 to 19.8% and 18.9 to 22.1% than that of wheat strip under NTSI2 and CTI treatments.It showed that the soil moisture had a tendency to flow from maize to wheat strips,and NTSI2 reduced the flow potential of soil moisture of two crop strips,compared to CTI treatment,during the wheat growth period.After wheat harvest,the averaged soil water potential of intercropped wheat strips was greater 24.3 to 31.3% than that of maize strips;and the soil water potential of intercropped wheat strip was greater 30.3 to 32.3% and 19.7 to 27.6% than that of wheat strip under NTSI2 and CTI treatment.It indicated that soil moisture had a tendency to flow from wheat to maize strips,and NTSI2 enhanced the flow potential of soil moisture of two crop strips,compared to CTI treatment,after wheat harvest.Therefore,NTSI2 had the advantage on weakening wheat strip competed soil water from maize strip and strengthening wheat strip compensated soil water for maize strip,in comparionsion to CTI.2.The maize strips had the greater soil water storage than wheat strips during the wheat growth period,but the wheat strips had the greater soil water storage than maize strips after wheat harvest.Soil water movement potential between intercrops strips at different growth stages leaded to water competition and complementary utilization at different spatial and temporal niches,and alternate strip mulching with no tillage straw and plastic film had the best regulating effect on weakening water competition and strengthening water compensation.Wheat strips competed for 14.5 to 29.8 mm and 27.4 to 69.5 mm soil water from neighboring maize strips before maize sowing and wheat-maize co-growth period,respectively.The treatment on NTSI2 decreased water competition by 25.8 to 43.3% and 37.3 to 58.9% in comparison to conventional intercropping treatment for the above two growth stages.However,maize independent growth period after wheat harvest,wheat strips compensated for 50.8 to 96.4 mm soil water to maize strips,NTSI2 treatment increased soil water compensation by 42.2 to 60.8% compared to conventional intercropping treatment.It showed that NTSI2 treatment had better regulating effect on soil water utilization between intercrops strips,and created the preferable foundation on soil water for high-yield of intercrops.3.Alternate strip mulching with straw and plastic film could enhance the effectiveness of water by reducing soil evaporation and the proportion of evaporation to evapotranspiration(E/ET)for the intercropping farmland.NTSI2 treatment significantly reduced soil evaporation by 9.0 to 17.3% than CTI.Soil evaporation of wheat strips was greater than that of maize strips across the entire growth period,and greater 23.1 to 122.7% before maize sowing,greater 28.8 to 44.9% during wheat-maize co-growth period,greater 84.1 to 143.9% after wheat harvest,respectively.In addition,NTSI2 reduced soil evaporation by 25.3 to 40.9%,7.4 to 18.9%,and 16.6 to 30.5% than CTI in intercropped wheat strip,during the above three growth stages.This result showed that reducing soil evaporation of wheat strip is of importance in wheat-maize intercropping system,especially after wheat harvest.NTSI2 treatment significantly reduced E/ET by 8.6 to 17.5%,compared to CTI.4.Intercropping can improve the leaf water use efficiency(WUEL)of wheat and maize,at the reproductive stage of two crops.NTSI2 treatment had relatively higher WUEL than else treatments,it had a potential for efficient use of water.At wheat reproductive stage,the WUEL of wheat in NTSI2 treatment was higher 5.4 to 14.6% than that in conventional monoculture wheat,and was higher 4.9 to 8.8% than that in conventional intercropped wheat.At maize reproductive stage,the WUEL was improved by 8.7 to 22.6% and 4.7 to 14.8% of maize in NTSI2,in comparison to conventional monoculture maize and conventional intercropped maize,respectively.5.Alternate strip mulching with straw and plastic film had the effects on decreasing the interspecific competition of wheat with maize,and enhancing compensation and super compensation effect of intercropped maize after wheat harvest.Alternate strip mulching with straw and plastic film decreased the aggressivity of wheat with maize by 8.6 to 30.9% compared to CTI;and NTSI2 had larger reducing effect,decreased by 27.1 to 34.8% over CTI.After wheat harvest,intercropped maize showed significant recovery growth effects,and crop growth rate(i.e.,CGR)was increased by 112.9 to 147.9% compared monoculture maize,and NTSI2 had greater CGR by 22.3 to 25.3% than CTI.Meanwhile,intercropping had higher contribution rate to grain yield(GCR)from each organ in maize than monoculture maize,and NTSI2 showed the most effect on GCR,increased by 9.6 to 22.2% from leaf,11.3 to 24.8% from stem,25.7 to 30.2% from sheath,and 24.8 to 34.8% from bract,respectively,compared to CTI.Although interspecific competition caused the weakening growth of maize during the co-growth period,after wheat harvest,intercropped maize achieved recovery growth because the compensation effect based on dry matter accumulation and second super-compensation effect based on dry matter translocation,especially NTSI2 had strong compensation and super-compensation effect.6.Intercropping had the obvious advantage of improving crop productivity and water utilization over monocultures.NTSI2 treatment exhibited the most significant effect on enhancing grain yield and water use efficiency(i.e.,WUE),improved grain yield by 13.8 to 17.1%,and WUE by 12.4 to 17.2%,respectively,compared to CTI.We concluded that no-tillage with 25 to 30 cm height of wheat straw covering in wheat strip and two-year plastic film mulching in maize strip is recommended as the best feasible cultural method for achieving high yield and water use efficiency in intercropping system,via optimizing soil moisture environment,increasing leaf area duration,improving crop photosynthetic rate,strengthening water compensation from wheat to maize strip,and enhancing the compensation and super compensation effect on the growth of maize,after wheat harvest. |
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