| Nitrogen application is the key to ensure the production of spring maize in Longzhong area.The low precipitation and uneven spatial and temporal distribution of spring maize production in the Longzhong region make it susceptible to the effects of natural precipitation,which,together with unreasonable nitrogen fertilizer application methods,causes low water and nitrogen use efficiency and soil nitrogen leaching in spring maize and other environmental problems,severely limiting the development of dry farming in the region.Therefore,spring maize sowing on whole plastic-film double ridges in rain-fed area was studied in this paper.Two fertilizer application types（urea and controlled release fertilizer）and three nitrogen application gradients were set:180 kg hm-2（U1）,225 kg hm-2（U2）and 270 kg hm-2（U3）for normal urea.Controlled release fertilizer 180 kg hm-2（CU1）,225 kg hm-2（CU2）and 270 kg hm-2（CU3）as well as urea treatment with 225 kg hm-2 nitrogen（CK）and no film coating（F）to study the effects of mulching method,N application type and N fertilizer dosage on soil hydrothermal conditions,spring maize growth and physiological processes,and water and N use efficiency,and based on the DNDC model multi-year（1981-2020）scenario simulation analysis,a nitrogen application program for spring maize with high water and nitrogen use efficiency in the study area was proposed,with the following main findings:（1）The characteristics of soil hydrothermal movement under mulching and N application were clarified,and the process of change in effective soil temperature and temperature difference between mulching and N application was quantified.The soil water content at 0-60 cm and 60-100 cm depths was 14.9%-29.9%and 4.0%-14.5%higher in the mulched treatments than in the unmulched treatments,respectively,throughout the spring maize reproductive period.Soil water storage at 0-100 cm was 12.0%to 23.1%higher in the mulched treatments than in the unmulched treatments.Soil warming was faster in the mulched treatments than in the bare ground treatment on typical sunny and cloudy days,and the daily temperature variation was less in the mulched treatments than in the bare ground treatment.The average soil temperature at 0-25 cm in both years was 6.24℃warmer than that of the non-mulched treatment at 0-30 d,and 1.94℃warmer at 60-90 d.The degree of change in average soil temperature per decade was similar for the different N treatments at all soil depths,indicating that different N application rates had less effect on soil temperature increase at different depths.The variation in soil temperature on typical days at each stage of fertility in spring maize showed that the difference in soil temperature between the mulched and unmulched treatments was always higher on typical sunny and cloudy days,and the difference between the two gradually decreased as the fertility period progressed.（2）The effects of mulching and nitrogen application on the growth and physiology of spring maize,yield and its composition and water and nitrogen use efficiency were comprehensively evaluated,and the optimum type and amount of nitrogen application for spring maize under the test year were obtained.Appropriate increase in N application could significantly improve plant height,leaf area index and chlorophyll content of spring maize.Plant height increased by an average of 2.3%,leaf area index by an average of 5.3%,chlorophyll content by an average of 2.6%and above-ground biomass by an average of 6.2%in the spring maize treatments applied at maturity in the volume year compared to regular urea.Compared to the regular urea treatment,the nitrate-nitrogen residues in the 0-40 cm soil layer were 31.3%lower on average and 76.6%lower on average in the 40-100 cm soil layer after harvest in the two-year spring maize treatment with controlled-release fertilizer.The average water use efficiency of the two-year spring maize mulching treatments was 69.8%to 172.4%and 66.4%to 202.7%higher than that of the non-mulching treatments,respectively,and the average nitrogen fertilizer bias productivity of the two-year controlled-release fertilizer treatments was 8.1%and 13.5%higher than that of regular urea,respectively.spring maize yield components in 2021 and 2022 were lower in the urea treatment than in the controlled-release fertilizer treatment.The two-year average yield of spring maize was 7.1%and 12.8%higher at 180 kg hm-2 of controlled-release fertilizer application compared to urea application,respectively.（3）An optimal tuning method based on genetic algorithm and DNDC model was constructed to analyse the effects of different nitrogen application types and amounts on spring maize yield,precipitation use efficiency and nitrogen fertilizer bias productivity,and to propose a reasonable nitrogen application scheme for spring maize in the study area.The rate and validated DNDC model could effectively simulate spring maize yield,soil moisture and above-ground biomass.The relative root mean square error（n RMSE）for yield ranged from 4.6%to 14.2%,the n RMSE values for soil moisture ranged from 7.0%to 17.4%and the R2 values for above-ground biomass ranged from 0.85 to 0.94,indicating that the DNDC model can simulate yield,growth and soil moisture changes of spring maize better.Scenario simulations showed that spring maize yield,N fertilizer bias productivity and precipitation use efficiency were all higher than other treatments at a controlled-release fertilizer application rate of 180 kg hm-2.Therefore,under the conditions of full-film double-monopoly furrow sowing,a controlled-release fertilizer application rate of 180 kg hm-2 was recommended as the best N application option for spring maize yield and high water and N use efficiency in the study area,taking into account crop yield,precipitation use efficiency and N fertilizer bias productivity. |
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