土壤水热变化对尿素迁移转化特性的研究

发布时间：2018-06-15 13:11

本文选题：温度梯度 + 水氮迁移　；参考：《太原理工大学》2017年硕士论文

【摘要】：由于大面积缺水、农田作物用水缺少合理科学的指导以及施肥技术水平的限制,导致了我国水资源大量浪费,肥料使用率普遍低下。养分随水分的大量流失,不仅使得作物产量低下,还对环境安全构成严重威胁;同时农田灌溉水温也是实际农业生产中对耕作、灌溉和排水产生影响的一个重要因素,灌溉水温不仅影响着作物的生长发育、土壤肥力以及土壤中水分和氮素的转化迁移,还影响作物对土体内水分和养分的吸收利用,及作物的生长发育和产量。只有同时兼顾土壤水、氮、热三者之间的关系,进行相关调控,才能满足作物的生长需要,提高作物产量。因此,开展灌水量,施肥量以及温度梯度耦合下土壤水氮热的分布特性试验研究,将为揭示不同因素间的耦合效应,增强氮素和水资源利用效率,促进农作物增产,制定科学合理有效的灌溉施肥制度提供重要的指导意义。本文通过室内土柱模拟试验,研究在不同温度梯度、不同灌水量及不同肥液浓度下土壤水热变化对尿素迁移转化规律的影响。主要结论如下:1、入渗率随时间延长而逐渐减小。在同一入渗时段内,入渗率随土壤灌水量、肥液浓度、温度梯度的增加均增加。2、随着入渗时间的增加,累积入渗量与湿润锋推进距离均增大。同一入渗时段内,累积入渗量与湿润锋推进距离随灌水量、肥液浓度及温度梯度的增大均增大。3、不同灌水量、不同肥液浓度以及不同温度梯度条件下的土壤含水率均表现为土柱上层含水率大于下层含水率,含水率随土层深度逐渐减小。在土层同一深度处,灌水量越大,含水率越高;温度梯度越大,含水率变化越明显,稳定时含水率最小;肥液浓度则对含水率影响不明显。随着时间的推移,土壤含水率随土深的分布逐渐变得均匀,含水率的变化逐渐趋于稳定。4、土壤温度随着时间的不断推移呈现先增后趋于稳定的特点,随土深的增加呈现不断减小的变化规律。同一温度梯度下,肥液浓度一定时,同一土深处,灌水量越大,土壤温度越高,达到平衡时所用时间越短,平衡温度越高,土壤温度随时间的变化过程满足T=a+b×3裻,随土深的变化则满足T=a×(?)(b|c-x|)+d,均具有较高拟合度。灌水量一定时,在相同温度梯度时,不同肥液浓度下的土壤温度随土深并无显著差别,肥液浓度对土壤温度的影响不大。肥液浓度及灌水量一定时,同一土深处,温度梯度越大,土壤的温度就越高,达到平衡时平衡温度越高,土壤温度随时间的变化过程满足T=a+b×3裻,随土深的变化则满足T=a×(?)(b|c-x|)+d,均有较高拟合度。5、灌水量、肥液浓度以及温度梯度三者越大,尿素的转化越快,所花费的时间越短。在土壤垂直剖面内,灌水量越大,尿素在土壤中分布越广,其迁移速率也就越快;肥液浓度越大,在土壤同一土深处,尿素含量就越大,肥液浓度对尿素的分布无显著影响;温度梯度越大,在土壤同一土层深度处,尿素态氮转化越快,剩余的尿素态氮含量越少,温度梯度促进尿素的转化分布。6、铵态氮在土壤中随时间呈现先增多后减小的变化规律,随土深的分布规律是先增大后减小,在不同土深位置处具有峰值,随灌后时间的推移,铵态氮与土深之间的变化过程均可以采用方程N_1=a×e~(b|h-c|)拟合,且具有较高拟合度。灌水量越大,土壤中25cm土深位置以上剖面内,铵态氮的含量越小;25cm土深位置以下剖面内,铵态氮的含量越大,铵态氮的分布范围越广。肥液浓度对铵态氮在土壤剖面中的分布影响较小,但对铵态氮含量大小影响较大,肥液浓度越大,铵态氮在土壤中含量越高。温度梯度对铵态氮具有较显著的影响,温度梯度越大,土壤中尿素生成铵态氮的速率就越快,铵态氮含量就越高。7、硝态氮在土壤中随时间呈现逐渐增大的变化规律,在土柱剖面中随土深的分布规律同样是逐渐增大。硝态氮主要积累于湿润锋处,且在时间的推移下随湿润锋向土壤下层迁移,灌水量越大,硝态氮向下运移越远,湿润锋位置处硝态氮含量越大。肥液浓度对硝态氮的分布影响不显著,主要影响其含量大小,肥液浓度越大,土壤中硝态氮含量就越高。温度梯度促进硝态氮的形成,温度梯度越大,土壤中硝态氮含量越高,转化形成硝态氮的时间越短,速率越快,硝态氮在土壤剖面主要积累于土壤底层,在不同灌水量及肥液浓度条件下,硝态氮含量随灌后时间的延长,与土深之间满足函数(?),具有拟合度较高;不同温度梯度下则与土深之间满足函数(?),同样具有较高拟合度。8、采用室内土柱模拟试验,定时监测土壤水氮热动态变化过程,运用BP神经网络算法构建的温度梯度条件下土壤水热、水氮热分布的预测模型均具有较高的精度和良好的稳定性,可以较好的描述温度梯度下土壤水氮热动态分布变化情况。
[Abstract]:Due to a large area of water shortage, the lack of rational scientific guidance for the water use of farmland and the restriction of the level of fertilization technology, the water resources in China are wasted and the fertilizer use rate is generally low. The loss of nutrients with the water is a serious threat not only to the low yield of the crops, but also to the environmental safety. At the same time, the temperature of the irrigation water is also real. It is an important factor affecting farming, irrigation and drainage in agricultural production. The irrigation water temperature not only affects the growth and development of crops, soil fertility and the transformation and migration of water and nitrogen in the soil, but also affects the absorption and utilization of water and nutrients in the soil, and the growth and yield of crops. The relationship between the three kinds of soil water, nitrogen and heat can be regulated to meet the needs of crop growth and increase crop yield. Therefore, the experimental study on the distribution characteristics of soil water and nitrogen heat under the coupling of irrigation amount, fertilizer amount and temperature gradient will reveal the coupling effect among different factors, enhance the utilization efficiency of nitrogen and water resources, and promote agriculture. In this paper, the effects of soil water and heat change on the migration and transformation of urea under different temperature gradient, different irrigation amount and different concentration of fertilizer are studied by indoor soil column simulation test. The main conclusions are as follows: 1, infiltration rate is gradually extended with time. In the same infiltration period, the infiltration rate increases with the amount of soil irrigation, the concentration of fertilizer and the temperature gradient increase by.2. With the increase of infiltration time, the cumulative infiltration and the distance of the wetting front increase. The increase of the cumulative infiltration and the wetting front distance is increased with the irrigation water, the increase of the concentration of fertilizer and the temperature gradient in the same infiltration period. The soil water content of large.3, under the different irrigation amount, the concentration of different fertilizer and the different temperature gradient conditions, is that the water content of the soil column is larger than the lower water content, and the water content decreases with the depth of the soil. The greater the water content is, the higher the water content is, the greater the temperature gradient, the more obvious the water content change and the water cut in the stable time. With the passage of time, the soil moisture content gradually became more uniform with the soil depth, and the change of water content gradually stabilized.4, and the soil temperature increased first and then tended to stabilize with the time. Under a temperature gradient, when the concentration of the fertilizer is certain, the greater the amount of water in the same soil, the greater the amount of water, the higher the soil temperature, the shorter the time for the balance, the higher the equilibrium temperature, the change of the soil temperature with the time of T=a+b * 3, which satisfies the T=a * (?) (?) (b|c-x|) +d with the change of soil depth. There is no significant difference in soil temperature between soil depth and soil depth at the temperature gradient. The concentration of fertilizer has little effect on soil temperature. When the concentration of fertilizer and the amount of irrigation are certain, the higher the temperature gradient is, the higher the temperature gradient, the higher the balance temperature is, the change of soil temperature satisfies T=a+b. With the soil depth change, it meets T=a * (?) (b|c-x|) +d, with higher fitting degree.5, the greater the irrigation amount, the concentration of fertilizer and the temperature gradient, the faster the urea conversion, the shorter the time it takes. In the vertical soil profile, the larger the amount of water is, the more the urea is distributed in the soil, the faster the migration rate is, the greater the concentration of the fertilizer is, the greater the concentration of the fertilizer liquid, the greater the concentration of the fertilizer, the greater the concentration of the fertilizer liquid, the greater the concentration of the fertilizer solution, the greater the concentration of the fertilizer, the greater the concentration of the fertilizer, the greater the concentration of the fertilizer liquid, In the same soil depth, the more urea content is, the concentration of fertilizer has no significant influence on the distribution of urea. The greater the temperature gradient, the faster the urea nitrogen transformation, the less the residual urea nitrogen content at the same soil depth, and the temperature gradient to promote the transformation of urea.6, and the ammonium nitrogen in the soil first increases and then decreases in the soil. The distribution law of soil depth first increases and then decreases, and has a peak value at different soil depth. The process of the change between ammonium nitrogen and soil depth can be fitted with the equation N_1=a x e~ (b|h-c|) with the change of soil depth. The greater the amount of water, the higher the depth of the soil in the soil, the ammonium nitrogen in the depth of the soil in the deep position of the soil 25cm. The smaller the content of the 25cm soil, the larger the ammonium nitrogen content and the wider distribution of ammonium nitrogen. The concentration of the ammonium nitrogen has little influence on the distribution of ammonium nitrogen in the soil profile, but it has greater influence on the ammonium nitrogen content, the greater the concentration of the fertilizer, the higher the ammonium nitrogen content in the soil. The temperature gradient is more significant to the ammonium nitrogen. The higher the temperature gradient, the faster the ammonium nitrogen of the soil in the soil, the higher the ammonium nitrogen content is.7, the nitrate nitrogen in the soil presents a gradual increase in the soil with time, and the distribution of soil depth in the soil column section is gradually increased with the soil depth. The wetting front migrated to the lower layer of the soil, the greater the amount of irrigation, the farther the nitrate nitrogen moved down, the more nitrate nitrogen in the position of the wetting front. The concentration of fertilizer had no significant influence on the distribution of nitrate nitrogen, which mainly affected the content of nitrate nitrogen, the higher the concentration of the fertilizer, the higher the nitrate content in the soil. The higher the nitrate nitrogen content in the soil, the shorter the transformation of nitrate nitrogen, the faster the rate, the nitrate nitrogen in the soil profile is mainly accumulated in the soil bottom. Under the conditions of different irrigation and fertilizer concentration, the nitrate nitrogen content is prolonged with the time of irrigation, and it has a higher fitting degree with the soil depth, and under the different temperature gradient, With the soil depth to satisfy the function (?), it also has a higher fitting degree.8, using the indoor soil column simulation test to monitor the dynamic change process of soil water and nitrogen heat, using the temperature gradient condition constructed by the BP neural network algorithm, the prediction model of the water and nitrogen heat distribution has high accuracy and good stability, and it can be better. The change of soil water and nitrogen thermal dynamic distribution under temperature gradient is described.
【学位授予单位】：太原理工大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：S158;S27

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