Study On The Water And Nitrogen Migration Regularity And Efficient Utilization Of Maize In The Salinity Soil

The salinity soil is widely distributed in our country. The serious shortage of water resources and the excessive application of nitrogen fertilizer limited the agricultural development. Increasing the water and fertilizer use efficiency and improving the salinity soil is the only way to realize the sustainable development of agriculture. The most of cultivated land in Inner Mongolia Hetao irrigation district is salinity soil and the amount of Yellow River water are decreasing year by year. The large application of nitrogen results in the salification of soil and the low utilization rate of water and nitrogen. The unreasonable scheduling of water and nitrogen has influenced the increase of crop yield directly. Currently, so many researchers have studied the water and nitrogen coupling, but most of them are studied in the non-salinzation soil. Under the combined action of salt stress and each other deficit of water and nitrogen, the mechanism of water and nitrogen coupling has changed. Setting different treatments of water and nitrogen in the different salinity soil, this paper studied the influences of water and nitrogen on the physiological and ecological index of maize, environment of farmland soil, migration pattern of water and nitrogen, water and nitrogen use efficiency in the different salinity soil. And the establishment of maize in water-nitrogen-Salt final yield, Jensen, BP neural network, the three models, and ultimately put forward for the local water and nitrogen production.It has significances to the increase of water and nitrogen efficiency in salinity district, saving water resources, reducing environmental pollution, preventing the secondary salinization, increasing the yield of maize in salinity district. The experimental research has made the following conclusions.(1)The increase of salt inhibited the growth of maize significantly. Increasing the irrigation and nitrogen properly could improve the plant height, leaf area, the accumulation of dry matter and reduce the root shoot ratio. When the irrigation amount exceeds2250m3/hm2and the nitrogen application exceeds225kg/hm2, the physiological indicators of maize doesn’t increase obviously or reduce slightly. The role of water on crop growth is more obvious in the salinity soil.(2) The increase of salinity decreases the photosynthetic capacity of maize and changes the photosynthesis of maize. The reasons for the midday depression of maize photosynthesis of different water and nitrogen treatments in different salinity soil are different. With the increase of salt, the reason of midday depression has changed into non-stomatal factor from stomatal factor. The path analysis shows the main factors which influence the diurnal changes of photosynthesis are different in slight and moderate salinity soil. In the salinity soil, the water is critical factor to determine the photosynthetic rate. Only the irrigation amount is suitable, the nitrogen fertilizer could play a role. In the slight and moderate salinity soil, the MWMN treatment (irrigation amount is2250m/hm2, nitrogen application is225kg/hm) not only keeps the high photosynthetic rate for a long time, but also makes the WUE of leaf reach the maximum value. Through comprehensive assessment of PCA and cluster analysis, the MWMN treatment could improve the photosynthetic capacity of maize well. From the point of comprehensive assessment, the ratio of water and nitrogen that irrigation amount is2250m/hm2and nitrogen application is225kg/hm2is conducive to the improvement of photosynthetic rate in salinity soil.(3)With the increase of salt, the water and nitrogen use efficiency decreases significantly. The nitrogen loss increases significantly. When the irrigation amount exceeds2250m3/hm2and the nitrogen application exceeds225kg/hm2, the water and nitrogen use efficiency and the nitrogen apparent loss of maize increases. The water and nitrogen efficiency of MWMN treatment (irrigation amount is2250m3/hm2, nitrogen application is225kg/hm2) is larger than the water and nitrogen use efficiency of other treatments and the nitrogen loss is less in the mild and moderate salinity soil. The yield of MWMN treatment is higher than the yield of other treatments in the two kinds of salinity soil. The yield of MWMN treatment in mild salinity soil is11581kg/hm2. The yield of MWMN treatment in moderate salinity soil is9015kg/hm2. Through the model optimization, the best schemes of water and nitrogen ratio are same in the mild and moderate salinity soil. The total irrigation amount is1900.95～2509.07m3/hm-2and the total nitrogen application is157.79-240.47kg/hm-2in the whole growth period. Compared with the local irrigation amount (2925m/hm-2) and nitrogen application (325kg/hm2), the water and nitrogen application of optimized project saved water18.2%～35%and saved fertilizer26.0%-46.4%. It provides the basis of saving water and fertilizer for planting maize in the salinization district.(4)The Jensen model of water-nitrogen-salt can satisfy the simulation accuracy. Furthermore, this model can show the influence of different water and salt on yield in different growth stage, which has the strongest practicability. It applies to the yield prediction of water and nitrogen treatment in salinity district.(5)The different application of water and nitrogen influence the soil water and nitrogen movement.The soil water content increases with the increase of irrigation amount in the two kinds of salinity soil. The soil water content decreases with the increase of nitrogen. When the nitrogen application exceeds225kg/hm2, the soil water content would increase.With the increase of irrigation amount, the soil layer where the peak of soil electric conductivity appears deepens. With the condition of the same irrigation amount, the electric conductivity of high nitrogen application is larger in the same layer.The nitrate nitrogen concentration in mild salinity soil is larger than the nitrate nitrogen concentration in moderate salinity soil. In the treatment of MWMN (irrigation amount is2250m3/hm2, nitrogen application is225kg/hm2), the nitrate nitrogen mainly accumulates in the40-60cm of soil layer in the two kinds of salinity soil. And the nitrate nitrogen concentration is easy to absorb for the maize root.The ammonium nitrogen concentration in moderate salinity soil is larger than the ammonium nitrogen concentration in mild salinity soil. The ammonium nitrogen mainly accumulates in the20cm of soil layer. The ammonium nitrogen concentration would increase with the increase of nitrogen application. The influence of irrigation on ammonium nitrogen is not significant.Through the calibration and testing, the HYDRUS-1D model could simulate the migration of water, salt and nitrogen well.Summing up the above, the irrigation amount is the main factor to influence the migration of water and nitrogen in salinity district. Based on the comprehensive analysis of growing index, photosynthesis, yield, water and nitrogen use efficiency of maize, consider the influence of salinity on the water and nutrient. Combined with the optimization of water and nitrogen dosage range, determine the best mode of water and nitrogen in the two kinds of salinity soil with the HYDRUS-1D model. The optimization of water and nitrogen dosage is that the irrigation amount is2250m3/hm2and the nitrogen application is225kg/hm2in the slight salinity soil. The optimization of water and nitrogen dosage is that the irrigation amount is2329.88m3/hm2and the nitrogen application is207kg/hm2in the moderate salinity soil.The research results can reveal the mechanism of water and nitrogen coupling. It provides the scientific theory basis for the improvement of water and nitrogen efficiency, saving water and fertilizer resources, reducing environmental pollution, preventing the secondary salinization, increasing the yield of maize in salinity district of Inner Mongolia Hetao irrigation district.