| The western of Jilin Province is located in western Songnen Plain with scarce precipitation and intensive evaporation. Because of the influence of climate and human factors, soil salinization is serious and the ecological environment is fragile. The unused land area accounted for more than half of the total unused land area of Jilin Province. In order to develop and utilize the waste salinization land resources in western of Jilin Province, land consolidation project was implemented that turn the saline-alkali waste land into paddy field. At present, the area of new development paddy field in the project area has reached 152000 hectares. However, it also creates new ecological environment problems. The management pattern is still extensive agriculture management measures. Soil secondary salinization, soil nitrogen migration and leaching problems have been caused as unreasonable irrigation and fertilization during the paddy field development process, which would not only reduce the nitrogen use efficiency and influence the rice yield, but also cause the groundwater and surface water pollution. Therefore, it is necessary to carry out reasonable water-fertilize management study to improve the utilization efficiency of water and fertilizer and increase rice yield, which is important to realize the sustainable development of agriculture.Choosing the Da'an irrigation area in western of Jilin Province as the study area,through data and samples collection and laboratory test, combined with classical statistics,geostatistics,and DSSAT model simulation methods, the research of soil water and nitrogen spatial distribution characteristics and behavior simulation was carried out, and the rice potential productivity was analyzed. The main content includes:(1) The spatial distribution characteristics and variation of soil water, soil water storage parameters and soil nitrogen were studied based on sample collection and test, and the effects of different land use types on the distribution characteristics of soil water content in different depth were analyzed. The results showed the non-saline soil moisture gradually decreased with depth on vertical, the saline-alkali soil moisture decreased at first and then increased. In the same layer non-saline soil moisture was lower than that of the saline-alkali soil. The nitrate-nitrogen content was strong variability and the ammonia-nitrogen content was medium variability. The soil nitrate-nitrogen decreased from East to West, and the ammonia-nitrogen in south area and north area is larger and it is lower in the center, while in East-West direction, the variation of ammonia-nitrogen concentration is less. The holding soil water storage, retained soil water storage and saturated soil water storage decreased from the periphery to the center, while the actual soil water storage increased from west to east and from north to south. It had larger spatial variability in north- south direction than in east-west direction.(2) The soil transfer function models between the soil water charateristics curve and soil basic physical and chemical properties were built through model fitting analysis using RETC and the empirical function model of soil moisture diffusivity curve was built through EXCEL software combined with experiment and data analysis, and the soil saturated hydraulic conductivity was obtained through soil transfer function models. The distribution characteristic and spatial variation were of the soil water charateristics curve, soil moisture diffusivity curve and soil saturated hydraulic conductivity were studied, at the same time the effects of salinization on soil hydraulic parameters were analyzed. Results showed that the soil moisture diffusivity curve in study area could be described with exponential functions and soil salt content had a significant effect on soil water diffusivity. When the soil moisture content is low(less than 0.3cm3/cm3), the soil moisture diffusivity increased with the soil salt content increased. The van Genuchten model was suitable to describe soil moisture retention curve in the study area. Saline-alkali soil layers 0-20 cm, 20-40 cm and 60-80 cm had a moderate variability of soil saturation moisture content, 40-60 cm and 80-100 cm belongs to the weak intensity variability, but the non-saline soil saturation moisture content of each layer of the section plane belonged to the weak intensity. Alpha values of saline-alkali soil and non-saline soil belonged to the moderate variability. Except n value of saline-alkali soil layer 80-100 cm belonged to the moderate-intensity variation, the others were weak intensity. The soil saturated hydraulic conductivity in saline-alkali soil profile increased with the increase of soil depth except the 60-80 cm layer, and it first increased and then decreased in non-saline-alkali soil peofile.Variability of soil saturated hydraulic conductivity of saline-alkali was larger than that of non-saline soil.(3) The rice DSSAT model in Da'an irrigation area was constructed based on database including weather, soil and crop genetic parameters, and was calibrated and validated with field data. Results showed that the DSSAT model could simulate the rice growth period and yield and soil water and nitrogen dynamics accurately, which indicate that the DSSAT model constructed could be used to study the soil water-nitrogen behavior and rice growth simulation in the study area.(4) The changing process of soil moisture under different irrigation modes and nitrogen levels was simulated using validated DSSAT model. Results showed that soil moisture variation amplitude in different layers was different and it decreased with soil depth increased. The variation amplitude of the surface layer was the largest. Within the same growing season, soil moisture content under intermittent irrigation methods was lower than that of normal irrigation methods. The variation amplitude of saline soil moisture was larger than that of non-saline soil. Fertilizer amount had the greatest effect on surface soil moisture content, and it almost has no effect on the bottom layer.(5)The dynamic changes of soil nitrogen of different irrigation modes were simulated by DSSAT model. The NO3-N decreased gradually in the surface soil layer, while it increased at first and then decreased in 20-100 cm layers during the returning green stage. Under the normal irrigation, after tillering, the NO3-N only increased in harvest stage in the saline-alkali soils and it increased in later tillering stage and harvest stage in nonsaline-alkali soils. Under intermitment irrigation, in 0-80 cm layers of saline-alkali soil, the NO3-N increased after applying tillering fertilizer, booting fertilizer and after harvest, and it only increased after applying booting fertilizer and after harvest in 80-100 cm layer. In non-saline-alkali soils, the NO3-N increased when after applying tiller fertilizer, flood-drying and harvest in 0-80 cm layers, and only increased in flood-drying stage and after harvest in 80-100 cm layer.(6)The NO3-N of saline-alkali soils after harvest under intermitment irrigation is larger than that of under the normal irrigation. For the non-saline-alkali soils, the NO3-N in flood-drying stage under intermitment irrigation is larger than that of under the normal irrigation, while after harvest the NO3-N under intermitment irrigation is less than that of under the normal irrigation.(7)The dynamic changes were almost the same between the two irrigation methods. The NH4-N content is the same from beginning to the time applying tiller fertilizer between the two irrigation methods, and then it is larger under normal irrigation especially in the stage from maturity to harvest.0-20cm: the NH4-N content increased rapidly to the peak value after applying tiller fertilizer, and then gradually decreased. After applying the panicle fertilizer and granular fertilizer, there was some increase of the NH4-N content and then it changes very small.20-40 cm and 40-60cm: except the stage of after applying the panicle fertilizer and granular fertilizer, it was almost the same with the 0-20 cm. in these two layers, there was no change after applying the panicle fertilizer and granular fertilizer.60-80 cm and 80-100cm: the soil NH4-N content gradually increased with time.There was some different between the saline-alkali soils and non- saline-alkali soils. During the flood-drying stage, the NH4-N content of non- saline-alkali soils was decreased significantly. From maturity to harvest stages, the NH4-N content increased first and then decreased in 0-60 cm layers, and was obviously larger than that of the jointing and booting stage.(8)The dynamic changes of soil NO3-N content in different levels of nitrogen application in the study area were simulated and analyzed using DSSAT model. The effects of nitrogen application level on soil NO3-N content were mainly showed in the harvest stage. In this stage, the soil NO3-N content increased with the increase of nitrogen application level when the nitrogen application was from 150kg/ha to 200kg/ha, and it decreased first and then increased when the nitrogen application was from 200kg/ha to 240kg/ha.The effect of nitrogen application level on soil NH4-N content was mainly showed in the time after the application of tiller fertilizer and the stage from the mature to harvest. When the application of nitrogen fertilizer ranged from 150kg/ha to 200kg/ha, the soil NH4-N content increased with the increase of nitrogen application level, and it decreased first and then increased when the nitrogen application was from 200 kg /ha to 240kg/ha.(9)Different combination of scenarios includes intermittent and conventional irrigation and 150kg/ha, 180kg/ha, 200kg/ha, 220kg/ha and 240kg/ha nitrogen applications were set to simulate the production potential and growth dynamics of rice by the DSSAT model. The yield increased with the increase of nitrogen application level when the nitrogen application level increased from 150kg/ha to 200kg/ha. When the nitrogen application rate increased from 200kg/ha to 240kg/ha, the yield first decreased, and then increased, and the yield of 200kg/ha was close to that of 240kg/ha. The results showed that the yield increasing effect of rice was not significant when the level of nitrogen fertilizer was more than 200kg/ha.The yield of rice was different under different irrigation methods and the same nitrogen application rate. When the level of nitrogen application was lower than 200kg/ha, the yield of conventional irrigation was higher than that of intermittent irrigation of non-saline-alkali land. And the smaller the amount of nitrogen applied, the greater the difference of yield. When the nitrogen application level was 200kg/ha to 240kg/ha, the yield was higher under intermittent irrigation. The yield of the conventional irrigation was significantly higher than that of the intermittent irrigation of saline-alkali land. And the higher the nitrogen application rate was, the greater the yield gap. Compared with the non-saline-alkali soil, the effect of saline-alkali soil under high water and fertilizer on yield was more significant.The results observed 2 kinds of water and fertilizer management mode with high rice yield and little influence on the environment. The combination of 200kg/ha nitrogen application level and intermittent irrigation was suitable for the management of rice cultivation in non-saline-alkali land, 200kg/ha nitrogen application level and conventional irrigation was suitable for saline-alkali land.The researches would provide certain scientific theoretical basis for water saving and fertilizer control, improve the soil salinization, preventing the groundwater and surface water pollution, and increasing the yield of rice. |
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