Optimized Irrigation And Fertilization For Winter Wheat And Summer Maize And Simulated Dynamic Characteristics Of Water And Nitrogen Transport At Deep Soil Depths Based On RZWQM2 Model In Guanzhong Irrigation Area

Water and nitrogen are important elements affecting crop growth and development.However,unreasonable irrigation and nitrogen application are prevalent in Guanzhong area,resulting in the lower utilization efficiency of water and nitrogen and causing a lot of water and nitrogen leaching,which caused groundwater NO₃^--N contamination.Therefore,adopting reasonable irrigation and fertilization management could increase water and nitrogen use efficiency and crop yield in the region,at the same time,reducing NO₃^--N pollution in groundwater.Thus,it is of great significance to ensure food security and sustainable development of agriculture.Focusing on the problems of lower water and nitrogen use efficiency and serious groundwater NO₃^--N pollution in the Guanzhong Plain of China,we carried out the research by the field experiments about different water and nitrogen treatment with summer maize and winter wheat in Jinghui canal irrigation area and combined with crop model simulation.The field experiment data were used to evaluate the adaptability of the RZWQM2 model in Guanzhong area.The appropriate irrigation period and nitrogen application amount under different precipitation years in the Guanzhong area were obtained based on RZWQM2 model using local long-term serial meteorological data.Revealing the effects of different irrigation quotas and nitrogen application on crop yields and water and nitrogen use efficiency,and the dynamics of soil water and nitrogen transport in deep soil layers?below the root layer?,and groundwater interface water and nitrogen exchange characteristic.Finally,we analyzed the meteorological factors affecting crop yield and water and nitrogen use efficiency and the soil texture factors affecting the characteristics of water and nitrogen transport in deep soil profile.These studies provide the basis for the efficient use of water and nitrogen resources in the region and also provide basis for groundwater NO₃^--N pollution control.The main research results are as follows:?1?The adaptability of RZWQM2 model in Guanzhong area was evaluated.The RZWQM2 model could better simulate soil moisture and soil nitrogen,with the values of n RMSE in the range of 5.7-21.6%,the index of agreement d in the range of0.55-0.96.And the model could better simulate the yields of winter wheat and summer maize,with the value of n RMSE and index of agreement d in the range of 7.2-11.1%and0.72-0.87%,respectively.However,the model has a poor simulation on LAI simulation,with the values of RMSE ranged in the 0.31-1.68 while the index of agreement d varied from 0.28to 0.94.The simulated values of crop water and nitrogen use efficiency agree well with the measured values,and the value of n RMSE in the range of 3.3%to 25.1%.?2?Obtained the appropriate irrigation dates and fertilization amount under different precipitation years in the Guanzhong Plain area.In the wet years and normal years for summer maize,seedling irrigation is the key to improve grain yield.However,in the dry years,two irrigations on the maize seedling and jointing stage was suggested to ensure higher maize yield.During the growth period of winter wheat,the jointing stage is the critical period of water demand for winter wheat.In order to ensure grain yield,two irrigations were suggested to carry out during winter wheat jointing and grouting stage to meet their need for water in the wet years.In normal years,three irrigations at wheat jointing,booting,and filling stages were recommended.In dry years,it is necessary to add one winter wheat tillering irrigation;Nitrogen application level has a great effect on crop yield.Under the wet years and normal years during summer maize,the interaction effect of irrigation amount and nitrogen application rate on maize yield was not significant.However,in the dry years,the demand for nitrogen in crops gradually increased with the increase of irrigation amount,the interaction effect of irrigation amount and nitrogen amount on yield was significant.During the winter wheat growth period under different precipitation years,the interaction effects of water and nitrogen supply on yield are significant,different water input scenarios have different effects on crop nitrogen uptake and utilization.In practice,it is suggested to appropriately adjust the application amount of nitrogen fertilizer according to the local water supply conditions.Thus,it is recommended that the suitable nitrogen application rates for winter wheat and summer maize are 240 and140 kg N ha-1.?3?Revealed the response laws of crop yield,water and nitrogen utilization efficiency to different irrigation quotas,fertilization application rates and meteorological factors.The irrigation quotas of 75-90 mm and 90-105 mm could guarantee higher grain yields and water use efficiency?WUE?for summer maize and winter wheat,respectively.Crop yield and nitrogen application rates conforms to linear-plus-plateau model,which showed both crops yield and WUE increased sharply and then increased slowly with the increase of nitrogen application rate.Crop nitrogen use efficiency?NUE?is more sensitive to irrigation,nitrogen application rate and time.The deep percolation loss of water and nitrogen were greatly affected by the irrigation amount and fertilization application rate,and the decreasing irrigation amount and increasing fertilization amount can reduce the deep loss of water to a certain extent.Under the different precipitation years during the crop growing period,there are large variabilities for different meteorological factors such as precipitation,radiation,temperature and relative humidity,and thus caused fluctuations in crop yields,water and nitrogen use efficiency.Under suitable water and nitrogen conditions,there is positive correlation between crop yield and radiation.The crop water consumption has a significantly positive correlation with radiation and temperature,and significant negative correlation with precipitation and relative humidity.WUE has a very significant negative correlation with temperature,and very significant positive correlation with relative humidity.There is a very significant negative correlation between the NUE of maize and temperature,and the significant positive correlation with relative humidity.The NUE of winter wheat has a very significant positive correlation with daily temperature,radiation,and significant negative correlation with relative humidity.In different precipitation years,there are some differences in the correlations between the indicators and meteorological elements.During the wet and normal years for summer maize,there is a positive correlation between crop yield and radiation,while there is no significant relationship in dry years.However,wheat yield showed a significant positive correlation with radiation only in wet years,but not in other precipitation years.?4?Defined the dynamic characteristics of water and nitrogen transport in deep soil under different irrigation and fertilization conditions.With the increase of irrigation quota,the deep soil water content and deep percolation water flux increased.When the irrigation amount increased from 60 mm to 135 mm,deep soil water content gradually increased from 0.247-0.252 cm³ cm^-3 to 0.282-0.283 cm³ cm^-3,the deep percolation water flux gradually increased from 0.021-0.024 mm d^-1 to 0.107-0.110mm d^-1.Moreover,with the increase of soil depth,the velocity of deep percolation water fit in the exponential decline relationship.And it increased with increasing irrigation amount,which showed the velocity of deep percolation water increased from 0.034-0.060 m d^-1 to0.077-0.153 m d^-1,as the irrigation amount increased from 60 mm to 135 mm.Respond time for 30 m groundwater depth from root layer was reduced from 2.4 years to 1 year.The accumulation and leaching of NO₃^--N in soil layers at different depths are greatly affected by the amount of irrigation and fertilization.As the amount of fertilizer increases,the amount of NO₃^--N accumulation and leaching flux in each soil layer gradually increased.With the increase of irrigation amount,the main accumulation depth and leaching depth of NO₃^--N continued to increase.When the irrigation increased from 60 mm to 135 mm,main NO₃^--N accumulation and leaching depth gradually increased from 2-10 m to 2-30 m.Under the lower irrigation amount conditions,excessive fertilization leads to increase soil NO₃^--N residues,which has little effect on 30 m depth groundwater.However,under the larger irrigation amount??105 mm?conditions,NO₃^--N could be gradually leached to the 30 m depth of groundwater,which lead to groundwater contamination even with lower nitrogen amount.?5?Obtained soil textural classes factors that affected the characteristics of water and nitrogen transport in deep soil depth.Under different soil textural classes profile,there is no significant difference in percolation water flux while significant difference in the water transport velocity in the deep soil layer.The lighter the soil,the faster the water transport velocity.Deep water transport velocity varies from 0.022 to 0.038 m d^-1 from 2 m to 30 m depth,and the respond time for percolation water transport velocity from 2 to 30 m was ranged from 2.02 to 3.48 years.It has a significant positive correlation with different soil pore size distribution and saturated hydraulic conductivity.There are significant different between the accumulation and leaching characteristics of NO₃^--N with different soil textural classes profiles.NO₃^--N is difficult to accumulate in the upper layer in sand and loamy sand profile due to larger soil pores,and the effect depth is at least reached 25-30 m.In the silty clay and clay profile,NO₃^--N was mainly accumulated in 5-10 m soil layers and difficult to transport to subsoil.In other loam profiles,the main accumulation depth and leaching depth of NO₃^--N are within15 m.The NO₃^--N leaching flux has significant positive correlation with soil pore distribution and saturated hydraulic conductivity,and the significant negative correlation with soil wilting water and field capacity.