| The supperabsorbent polymer for water saving in agriculture is gradually applied to agricultural production, which has bright prospects of water conservation, drought resistance and improvement in water and fertilizer use efficiency.The nutritional and drought-resistant supperabsorbent polymer developed by Henan Academy of Agricultural Sciences was applied in the potted trial and field tests. In this paper, the influence of coupled utilization of supperabsorbent polymer and nitrogen fertilizer on the structural characteristics, water retention and delivery of soil, the physiological and biochemical characteristics of wheat and the water and fertilizer use efficiency is primarily analyzed.The preliminary results obtained from the tests are as follows:1. The stimulation effects of wheat in field tests indicate that the supperabsorbent polymer promotes the growth of wheat, manifested in the increase in the leaf area, wheatear and the decrease in the water consumption, which ultimately leads to bigger production and water use efficiency. The compound effects of supperabsorbent polymer and nitrogen fertilizer are better than the control group, with the increase in agricultural production by 54.8% and water use efficiency by 71.5%. And the productivity of nitrogen is also obviously increased. Among the treatments, the supperabsorbent polymer of 60kg/hm2 coupled by the nitrogen fertilizer of 225kg/hm2 can obtain the best results. The potted trial results show that the increase in wheat yield is not obvious with supperabsorbent polymer only added to soil under various moisture conditions. But the yield can increase significantly with nitrogen fertilizer and supperabsorbent polymer added to the trial. The treatment with medium nitrogen fertilizer and sufficient irrigation is higher than that under mild water stress. Under mild water stress condition, it results in the increase in yield by 78.9% and water use efficiency by 77.6% while the increase in yield by 98.2% and water use efficiency by 97.6% under sufficient irrigation. Moreover, the water use efficiency under mild water stress is higher than that under sufficient irrigation.As to the agricultural efficiency, apparent recovery and productivity of nitrogen fertilizer, the treatment with supperabsorbent polymer of 27mg/kg and nitrogen fertilizer of 432mg/kg under mild water stress condition can achieve best results but the treatment with supperabsorbent polymer of 54mg/kg and nitrogen fertilizer of 432mg/kg under sufficient irrigation can also obtain good results.2. The structural characteristics and porosity of soil in the tests proves that the supperabsorbent polymer obviously improves the stability of soil structure and reduces the bulk density. The utilization of nitrogen fertilizer can also promote the structural stability of soil. In field tests, it results in higher content of the water-stable aggregates (d>0.25mm) and more stable soil structure under the treatment of supperabsorbent polymer of 60kg/hm2 and coupled utilization of supperabsorbent polymer of 60kg/hm2 and nitrogen fertilizer of 225 kg/hm2. But in potted trial, the stability of soil structure decreases with growth of wheat. The structural stability of soil under mild water stress condition is more stable than that under sufficient irrigation. It shows significant increase in water-stable aggregates under the treatment of coupled utilization of supperabsorbent polymer of 54mg/kg and nitrogen fertilizer among the treatments.In potted trial, the quantitative examination in soil porosity by CT scanning technique indicates that the coupled utilization of supperabsorbent polymer and nitrogen fertilizer leads to remarkable increase in the number of macro void, macro porosity and circle forming ratio of soil. The number of macro void and macro porosity under mild water stress condition is much higher than that under sufficient irrigation. And the total porosity and macro porosity tend to grow under the treatment of coupled utilization of supperabsorbent polymer of 54mg/kg and nitrogen fertilizer of 432mg/kg under mild water stress, which results in the increase in the total porosity by 57.3% and macro porosity by 60.7% as to the control group. But under sufficient irrigation, it can achieve better results with supperabsorbent polymer of 54mg/kg and nitrogen fertilizer of 864mg/kg, manifested in increase in the total porosity by 55.4% and macro porosity by 116.7%. It shows that under various moisture contents, the appropriate utilization of supperabsorbent polymer and nitrogen fertilizer can effectively improve the soil porosity and promote the moisture and nutrient assimilation and growth of crop.3 The moisture characteristics of soil in potted trial show that the relationship between moisture content and soil water suction under the coupled utilization of supperabsorbent polymer and nitrogen fertilizer can be described by the functionθ=a·S-b and the water retention tends to be more obvious. Under mild water stress condition, the water retention is enhanced with quantity of supperabsorbent polymer while the water retention in control group is lowest under sufficient irrigation but the difference among the other treatments tends to diminish. While the utilization of supperabsorbent polymer improves the water retention, water conductivity and the water use efficiency. The water delivery under mild water stress is inferior to that under sufficient irrigation. The moisture absorbed and used by crop from the supperabsorbent polymer under mild water stress can be increased by 36.8% with the coupled utilization of supperabsorbent polymer of 81mg/kg and nitrogen fertilizer of 864mg/kg while 13.41% increase under sufficient irrigation with the supperabsorbent polymer of 27mg/kg and nitrogen fertilizer of 864mg/kg.4. The influence of supperabsorbent polymer and nitrogen fertilizer on the physiological and biochemical characteristics reveals the compound effects in the mechanisms of growth of wheat and the increase in yield.With natural precipitation in field tests, the utilization of supperabsorbent polymer and nitrogen fertilizer increases the relative moisture content of wheat leaf and chlorophyll content while the soluble sugar content, proline content and permeability of membrane of wheat leaf and root system are decreased and ultimately enhance the drought resistance of wheat. The comprehensive reflection of all treatments shows that the coupled utilization of supperabsorbent polymer of 60kg/hm2 and nitrogen fertilizer of 225kg/hm2 can attain good results. In jointing stage, the water use efficiency of wheat leaf is higher with the simple treatment of nitrogen fertilizer of 450kg/hm2 with the increase by 60.7% as to the control group and 52.1% with the utilization of supperabsorbent polymer of 60kg/hm2 and nitrogen fertilizer of 450kg/hm2. In the watery stage, the water use efficiency with the simple treatment of supperabsorbent polymer of 30kg/hm2 with the increase by 123.5% as to the control group and 120.4% with the utilization of supperabsorbent polymer of 60kg/hm2 and nitrogen fertilizer of 225kg/hm2. It shows that the supperabsorbent polymer can improve drought resistance of wheat in the different growth stage, retard the damage caused by water stress, and promote the accumulation of dry matter.In potted trial, the photosynthetic and physiological responses of wheat before and after rehydration under various moisture contents are as follows:Before the rehydration, the photosynthetic rate, evapotranspiration rate and stomata conductance in jointing stage with the nitrogen fertilizer of 864mg/kg only added to soil under mild water stress are higher. But under sufficient irrigation, the nitrogen fertilizer with high content slows the photosynthetic rate and evapotranspiration rate but the greater decrease amplitude results in higher water use efficiency of leaf. The photosynthetic rate of wheat with supperabsorbent polymer and nitrogen fertilizer is relatively low but higher than the control group. In booting-flowering stage and watery stage, it can promote the photosynthetic rate, evapotranspiration rate and stomata conductance of wheat with supperabsorbent polymer applied to potted trial before rehydration while it attains good results with supperabsorbent polymer of 54mg/kg under mild water stress. But under sufficient irrigation, the photosynthetic rate with supperabsorbent polymer of 27mg/kg is maximizing. After rehydration, the photosynthetic parameters of all treatments obviously improves but the photosynthetic rate, evapotranspiration rate, stomata conductance and water use efficiency of leaf increase with the soil water decreased to a certain degree in different growth stages.The comprehensive analysis indicates that the utilization of nitrogen fertilizer intensifies the moisture stress for the growth of wheat in mid-later stage, which leads to decrease in the photosynthetic parameters, e.g. stomata conductance, but the photosynthetic and physiological stimulation effects after rehydration tends to grow and the proper moisture stress can promote the water use efficiency of wheat leaf.5. Path analyze on the relationship between grain yeild and indexes such as soil physical, wheat physiological and wheat growth indicates: soil hold water ability, water supply capacity, hydraulic conductivity and field capacity become the influencing factors on wheat grain yield, and the effect of mild stress condition is better. Economic benefit analysis shows that there is the most significant effect of the 60kg/hm2 dosage wih supperabsorbent polymer for yield, and the maximum VCR and income are 7.05 and 1317.6 yuan respectively.
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