Yield Regulation And Soil Water And Crop Yield Simulation Under Mulched Drip Irrigation

Mulched drip irrigation（MDI）has been widely employed in arid and semiarid regions for crop cultivation to accurately supply water and fertilizer in the soil in conjunction with soil evaporation reduction.However,“accurately supply”does not means“high efficiency supply”.Poor soil aeration,to low root shoot ratio,and extremely hot and dry soil away from the drip tube caused by MDI may lead to premature senescence and decreased yield.Crop root is an important organ absorbing water and nutrients,soil-root/shoot ratio-air system is becoming a focus for crop requirement diagnosis of soil water and nutrients.So,exploring soil water and nitrate distribution and crop root/shoot ratio will contribute to improving the mechanism of crop yield regulation.The maize（Zea mays L.）cultivar“Ximeng 6”was employed in this field study in Hetao irrigation district from 2014 to 2016.Two levels of lateral layout were arranged in this study:one lateral laid on the surface,centered between corn rows with a lateral spacing of 1.0 m（S1）,and laterals were placed close to the crop row with a lateral spacing of 0.5 m（S2）.Besides,two film-covering modes（M1:fully mulched,M2:partially mulched）were also arranged:In S1 and S2 treatment,soil was partially mulched at 60 percent cover degree with plastic film at a width of 60 cm and 30 cm,respectively.Plots with lateral layout of S1without mulching were also arranged as control treatment.Soil water and NO₃^--N distribution,crop height,stem diameter and leaf area index were measured during the entire growth stage.Also,relative chlorophyll content of leaf was measured at six leaf stage and sliking stage,and root length and surface area were also measured at sliking stage.This study aimed to investaged the effect of lateral layouts and film-covering modes on the soil moisture and NO₃^--N distributions and how shoot-root growth and crop yields were affected by different layouts and film-covering modes in mulched,drip-irrigated maize under arid climatic conditions.Seedling emergence is also a very important factor for crop yield enhancement.So,we also investgated the effects of plastic film covering with different wides on soil thermal time and accumulated seedling emergence rate of spring maize.Lastly,this study built an improved Root Zone Water Quality-SHAW Model（RZ-SHAW）version which can simulate soil processed and crop growth under mulched drip irrigation system.The total applied irrigation of the mulched drip treatments was 60%of the average,local irrigation application in 2014 and scheduled according to evapotranspiration（E20 pan）in 2015 and 2016.The irrigation amounts were 180,346.1,and 223.9 mm in 2014,2015,and 2016,respectively.In 2015,frequent fertigation was adopted after jointing stage.In both years,the total N application rate was 300 kg N ha^-1 for all treatments and diammonium phosphate was spread at level of 200 kg P₂O₅ ha^-1 as a base fertilizer before mulching in both years.The main achievements of this thesis are as following:（1）lateral layout exerted notable effects on soil moisture and soil water distribution uniformity（CU_w）while mulching modes did not.Soil moisture differences among treatments were showed at 40 cm soil depth,while the CU_ws were significant different at both 40 cm and60 cm soil depth.The distribution uniformity of soil NO₃^--N（CU_n）was not always improved by fertigation,and the CU_n decreased under frequent fertigation.Compared with CU_w,CU_nshowed more sensitively responds to lateral layout and mulching modes.Frequenct fertigation led to inconsistency between CU_nand CU_w.（2）The effects of soil water conservation and temperature enhancement gradually decreased as the plastic film width decreased,and plastic film mulching played a more obvious temperature enhancement effect under arid region with high air temperature.In NM treatment,the calculated effective growing degree days（EGDD）was 5.3℃lower than that of in mulching treatments.It maybe because the critical value of soil water stress（60%of field capacity）is highly setted.In addition,soil moisture may impose a non-liner regulation on GDD,instead of liner relationship.The Gompertz nonlinear regression of cumulative relative seedling emergence（CRE）and EGDD was applicable in mulching treatments,however,the performance of the CRE prediction for the NM treatment was not as accurate as it was for mulching treatments.It was mainly because germination was suppressed in NM treatment and the process of seedling emergence was shorten by the adverse soil water and thermal conditions.（3）Mulching significantly increased root length density（RLD）in the shallow soil layer:the RLD at 0–20 cm depth in full mulching and partially mulching treatments were 32.9%and36.8%higher than NM treatments,respectively.Lateral layout exerted notable effects on RLD than mulching modes.The RLD at 0–40 cm depth and 40–80 cm depth in S1treatements were 13.9%higher and 38.6 lower than that of in S2 treatments.In 0–40 cm soil depth,the RLD in the S2 treatments was higher than S1 treatments in the zone around main root and lower than in S1 in the zone away from main root.Under the 40 cm soil layer,the RLD in S2 treatments was higher than S1 treatments in all the horizontal measure points.The result of root surface area was consistent with RLD,it indicated that lateral layout and mulching modes affected RLD and imposed little regulation on root diameter.（4）Plant height（Plt Ht）,stem diameter（SD）,leaf area index（LAI）and relative chlorophyll content（RCC）were measured at 10 leaf stage（V10）and milk stage（R1）to investigate plants growth.The Plt Ht,SD,LAI,and RCC in mulching treatments were higher than that of in no-mulching treatment in both types of fields.In all mulching treatments,differences of Plt Ht and LAI were obviously showed just at V10 stage.Plt Ht in full mulching treatments were 10.1%and 17.7%higher than that of in partial mulching treatment in 2014and 2015 respectively,as well as 22.5%and 15.1%of LAI.Differently,plants in full mulching treatments showed significant lager SD and RCC than that of in partial mulching treatments at both V10 and R1 stages.Plant SD in full mulching treatments were 12.0%and11.1%higher than that of in partial mulching treatments at V10 stage in 2014 and 2015,respectively.The RCC in full mulching treatments were 23.2%and 19.2%higher than that of in partial mulching treatments at V10 stage in 2014 and 2015,respectively.Plant SD in full mulching treatments were 7.3%and 6.9%higher than that of in partial mulching treatments at R1 stage in 2014 and 2015,respectively.The RCC in full mulching treatments were 18.1%and 19.3%higher than that of in partial mulching treatments at R1 stage in 2014 and 2015,respectively.Remarkably,lateral placement（S1 or S2）also significantly affected RCC,which was different from plant height,stem diameter,and LAI.The ratio of root surface area and leaf area in mulching treatments were higher than NM treatment,and root surface area and leaf area showed a positive correlation.Lateral layout imposed more effect on the ratio of root surface area and leaf area compared with mulching modes.The“area index”better reflected the effects of soil water and nitrate on crop growth.However,soil water,soil nitrate,and crop growth showed no correlation under frequent fertigation.（5）Crop yields in mulching treatments were higher than that of in NM treatment under both high and low fertigation:plastic film mulching enhanced kernel numbers per plant（KNP）and hundred-grain weight（HGW）compared with NM treatment.Besides,the improvement of seedling emergence was also a reason for yields enhancement in mulching treatments.Under low frequency of irrigation,the grain yields in full mulching treatments and lateral layout of S2 were 30.5%and 18.7%higher than that of in partial mulching treatments and lateral layout of S1,and the grain yields in full mulching treatments were 30.5%higher than that of in partial mulching treatments.However,the grain yields in all mulched driped irrigation treatments were no significantly different under high frequent irrigation.Under low frequency of irrigation,full mulching increased both KNP and HGW while lateral layout just significantly affected KNP.Crop yields showed close positive correlation with CU_n,so,CU_nshould be attempted to increase for fertigation system design.Considering grain yields and input-output ratio,Frequent fertigation（i.e.once every three days）after jointing is preferentially recommended S1M2,if frequent fertigation is infeasible,S1M1 can be a good choice under low frequency fertigation.（6）The RZ-SHAW_-PMshowed well predictions for soil water content,soil evaporation,crop water consumption,LAI,and grian yield.The RZ-SHAW_-PMshowed well responds to rainfall,irrigation events and plastic coverage ratio,so it can be a useful tool to guide irrigation,fertilization,and mulching covering methods under mulched drip irrigation system.