| Inner Mongolia Hetao irrigation district is located in middle-up reaches of the Yellow River.It is an important grain production base in northern China.The maize is one of the most important grain crops and its planting area ratio is 14.5%.To pursuit the high production,the local people irrigated and applied nitrogen fertilizer excessively for years,which led to the low water and nitrogen use efficiency and the significant decline of production-enhancing benefits.A series of problems of ecological environment pollution and resource waste which were caused by the unreasonable water-nitrogen management regimes blocked the environment-friendly and resource-saving agricultural production that the Hetao irrigation district would develop.Therefore,it would be significant to determine a reasonable water-nitrogen management regime for achieving the goal in Hetao irrigation district.The goal means saving water and nitrogen,achieving high yield and high efficiency and ensuring the environmental protection.The field experiment was carried out in Hetao irrigation district for two years of 2014 and 2015.The field experiment adopted randomized block design and set fifteen water-nitrogen management regimes.It discussed and analyzed the response of spring maize-soil system to different water-nitrogen management regimes.The research applied the DSSAT-CERES-Maize model to simulate the attainable grain yield with different water-nitrogen management regimes.Finally,it determined a best water-nitrogen management regime which could balance the high yield,high efficiency,environment-friendly and resource saving.The results of this research are as following.(1)The dry matter accumulation aboveground of treatments in the whole growth period of spring maize showed a change trend of "S" type.The increasing range of dry matter accumulation aboveground reached its maximum in the stage of spring maize from tasseling to filling.In the growth period of spring maize,the net photo synthetic rate,transpiration rate,LAI and SPAD showed a curvilinear change with one peak.The values of these indexes increased at first and then decreased.And the peak values were shown in tasseling stage.The proper irrigationg quota and nitrogen application could increase the net photosynthetic rate of spring maize significantly and extend the photosynthetic function period of leaves.The water-nitrogen management regimes of W2N3(irrigation quota:750 m3·hm-2;nitrogen application:240 kg·hm-2)relieved the decline rate of LAI,SPAD and enhanced photosynthetic preoperty effectively,which provided guarantee for high yield of spring maize.(2)In the year of 2014 and 2015,the increasing yield rate of nitrogen treatments increased significantly with the increase of nitrogen application when the irrigation quota was constant.The increasing yield rate of nitrogen treatments decreased slightly with the increase of nitrogen application when the nitrogen application was constant.When the irrigation quota reached to 750 m3·hm-2 and nitrogen application reached to 240 kg·hm-2,the much more irrigation amount and nitrogen application would not bring the effect of increasing yield.When the irrigation quota was constant,the water use efficiency and irrigation water use efficiency of treatments increased with the increase of nitrogen application.When the nitrogen application was constant,the water use efficiency and irrigation water use efficiency of treatments decreased with the increase of irrigation quota.When the irrigation quota was constant,the nitrogen use efficiency and NPFP of treatments decreased with the increase of nitrogen,application.When the nitrogen application was constant,the nitrogen use efficiency and NPFP of treatments increased with the increase of irrigation quota.(3)The NO3--N accumulation of nitrogen treatments in 0-100 cm soil layerunderground increased with the increase of irrigation quota and nitrogen application.And the NO3--N migrated downward to the deep layer obviously with the advancement of growth period.In the 0-80 cm soil layer underground,the increasing range of NO3--N accumulation which caused by the increase of nitrogen application was larger than the increasing range of NO3--N accumulation which caused by the increase of irrigation quota.When the irrigation quota was constant,the NH4+-N accumulation increased with the increase of nitrogen application.When the nitrogen application was constant,the differences of H4+-N accumulation of treatments with different irrigation quota were not significant.In the year of 2014,the NO3--N accumulation in 0-100 cm soil layer underground accounted for 81,54%?83.61%of inorganic nitrogen accumulation.In the year of 2015,the NO3--N accumulation in 0-100 cm soil layer underground accounted for 81.70%-85.86%of inorganic nitrogen accumulation.The soil NO3--N accumulation of treatments were much larger than the soil NH4+-N accumulation of treatments.(4)With the increase of nitrogen application,the two years' average increase of NO3--N concentration by W1 was far below the two years' average increase of NO3--N concentration by W2 and W3 within the depth of 0-40 cm.With the increase of irrigation quota.the average increase of NO3--N concentration by N1 and N2 were far below the average increase of NO3--N concentration by N3 and N4 within the depth of 0-40 cm.Compared with the treatments in 0-40 cm depth,the NO3--N concentration of treatments showed an overall declination within the depth of 40-80 cm.But the change trend of NO3--N concentration was consistent with the depth of 0-40 cm.Within the depth of 80-120 cm,the leaching loss of NO3--N was significantly influenced by the nitrogen application,irrigation quota,and the interaction of those two elements.When the irrigation quota was constant,the NO3--N leaching loss of 2014,2015 increased with the increase of nitrogen application.The NO3--N leaching rate of 2014,2015 increased at first and then decreased with the increase of nitrogen application.When the nitrogen application was constant,the NO3--N leaching loss and NO3--N leaching rate of 2014,2015 increased with the increase of irrigation quota.(5)The peaks of ammonia volatilization rate after dressing fertilization of the same treatment are larger than the peaks of ammonia volatilization rate after sowing fertilization in the year of 2014 and 2015.The peaks of ammonia volatilization rate after dressing fertilization are 63.31%and 62.06%respectively higher than the peaks of ammonia volatilization rate after sowing fertilization.The nitrogen application,irrigation quota,and the interaction of those two elements all have highly significant influence on ammonia volatilization loss.And the influence of the three factors on ammonia volatilization loss shows is the regime of nitrogen application>irrigation quota>interaction of those two elements.The average ammonia volatilization loss of all nitrogen treatments after sowing fertilization are 5.71?13.95 kg·hm-2 in the year of 2014 and 2015.The average ammonia volatilization loss of all nitrogen treatments after dressing fertilization are 8.70?18.66 kg·hm-2 in the year of 2014 and 2015.Thetotal ammonia volatilization loss of all nitrogen treatments are 13.90?32.21 kg·hm-2 in the year of 2014.The total ammonia volatilization loss of all nitrogen treatments are 15.45?32.99 kg·hm-2 in the year of 2015.(6)The DSSAT-CERES-Maize model could simulate the phenophase,final biomass aboveground and grain yield precisely.The simulation results of soil moisture content were accuracy.And the simulation curve of soil volumetric moisture content of treatments had a similar change trend with the measured values.With the increase of irrigation quota,the simulation results of model on soil moisture content were more precise.The simulation precision of DSSAT-CERES-Maize model on dynamic change of biomass aboveground and LAI were relatively low.Through the sensitivity analysis of attainable grain yield,the attainable grain yield would not increase with the increase of irrigation quota and nitrogen application when the irrigation quota reached 85 mm and the nitrogen application reached 280 kg·hm-2.(7)The treatment of W2N3 could not only save water,nitrogen and obtain stable yield,but also could maintain a higher water-nitrogen use efficiency.And it could also reduce the nitrogen pollution to the groundwater and atmosphere significantly.Considering the aspects above,this research recommends the treatment of W2N3(W2:750 m3·hm-2.N3:240 kg·hm-2)as the best water-nitrogen management regime for experimental district.It could balance the high yield,high efficiency,environment friendly and resource saving.The optimal water-nitrogen management regime(nitrogen application is 280 kg·hm-2;irrigation quota is 85 mm)that DSSAT-CERES-Maize recommends is similar to the water-nitrogen management regime that field experiment recommends. |
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