Metahara is the largest sugarcane farm in Ethiopia. It produces around 120,000 tons of sugar per year. The farm has been facing some problems such as salinity and sodicity, which has been studied by different experts ...Metahara is the largest sugarcane farm in Ethiopia. It produces around 120,000 tons of sugar per year. The farm has been facing some problems such as salinity and sodicity, which has been studied by different experts for several decades. However, the other universal problem of agricultural farms is nitrate leaching loss, which has never been studied in the site, owing to lack of resources and expertise. The amount of nitrate leaching from agricultural farms can be measured directly from drainage rates or estimated by using numerical models. Measurements of drainage flow can be done by using lysimeters, but normally it can be estimated from water balance calculations or from field measurements of hydraulic gradients and hydraulic conductivities. However, in reality, hydraulic conductivity is highly variable and measurements in the field can be very laborious. Moreover, predicting nitrate leaching losses by using numerical models from such data- poor study area is also another problem. Nevertheless, groundwater nitrate concentration of the farm is measured by using the UV screening and distillation methods. Using the experimental results as an input for the model calibration, the amount of nitrate leaching from the farm is predicted for a 47 years of simulation period using the LEACHN model. In this case, both the measured and predicted values of nitrate leaching losses show that there is no nitrate problem in the site. However, even though the likelihood of detecting nitrate contamination in the study area is low, potential anthropogenic nitrogen sources must be carefully managed, for it is better to be safe than regretful.展开更多
突破厚包气带农田根层氮磷淋溶与地下水污染复杂定量关系和阻控机理是国际研究难点。本文系统梳理了重点研发专项"农田氮磷淋溶损失污染与防控机制"项目取得的主要进展,项目包括以下4方面研究内容:1)北方主要农区农田根层氮...突破厚包气带农田根层氮磷淋溶与地下水污染复杂定量关系和阻控机理是国际研究难点。本文系统梳理了重点研发专项"农田氮磷淋溶损失污染与防控机制"项目取得的主要进展,项目包括以下4方面研究内容:1)北方主要农区农田根层氮磷淋溶时空规律;2)根层-深层包气带氮磷淋溶机制和主控因子;3)黑土、潮土和褐土氮磷淋溶阻控机制及其效果;4)典型农区氮磷淋溶风险与区域消减途径。主要科学发现包括:1)受土地利用类型、地下水埋深、包气带岩性、水文地质条件等综合因素的影响,黑土区、潮土区和褐土区根层氮磷淋溶规律与地下水硝酸盐超标率体现出空间不一致和较大差异性。黑土区虽然根层淋溶较小,然而受地形地貌影响,地下水水质对淋溶响应更强烈,应该进一步研究黑土区地下水水质对淋溶的响应机制。华北潮土区和褐土区厚包气带具有明显氮阻控能力,应该进一步加强厚包气带对氮磷淋溶减排机理与途径研究。2)基于长期施肥定位试验和12 m深观测井对包气带农田土壤氮盈余累积特征和淋失规律的研究发现,华北平原区的环境安全施氮量约为200kg(N)·hm-2·a-1,超过环境安全阈值的多投入氮肥中有51%淋失到1m根层以下,不合理灌溉、强降水、大孔隙和裂隙是造成土壤硝酸盐淋溶的主要因素,对包气带累积硝态氮的淋失作用可影响至6m以下土层。3)利用深层取样和生物学方法结合,对厚包气带0~10.5m原位土壤微生物的反硝化活性和微生物区系组成的研究结果表明,表层土壤是微生物进行反硝化的主要场所,深层土壤中反硝化作用显著减弱,"碳饥饿"是限制底层土壤反硝化微生物丰度与活性的关键因素;室内培养试验证实添加碳源可有效激活土壤微生物的反硝化活性,为"根层截氮包气带脱氮"的淋溶阻控机理找到了突破口。4)利用黑土、潮土和褐土区氮磷淋溶阻控试验、全国农业面源污染国控监测网、北方农区地下水硝酸盐监测网和NUFER (NUtrient flows in Food chains, Environment and Resourcesuse)模型,提出了养分损失脆弱区区划和区域氮磷污染削减草案,可为农业绿色发展和面源污染阻控提供科学依据。展开更多
文摘Metahara is the largest sugarcane farm in Ethiopia. It produces around 120,000 tons of sugar per year. The farm has been facing some problems such as salinity and sodicity, which has been studied by different experts for several decades. However, the other universal problem of agricultural farms is nitrate leaching loss, which has never been studied in the site, owing to lack of resources and expertise. The amount of nitrate leaching from agricultural farms can be measured directly from drainage rates or estimated by using numerical models. Measurements of drainage flow can be done by using lysimeters, but normally it can be estimated from water balance calculations or from field measurements of hydraulic gradients and hydraulic conductivities. However, in reality, hydraulic conductivity is highly variable and measurements in the field can be very laborious. Moreover, predicting nitrate leaching losses by using numerical models from such data- poor study area is also another problem. Nevertheless, groundwater nitrate concentration of the farm is measured by using the UV screening and distillation methods. Using the experimental results as an input for the model calibration, the amount of nitrate leaching from the farm is predicted for a 47 years of simulation period using the LEACHN model. In this case, both the measured and predicted values of nitrate leaching losses show that there is no nitrate problem in the site. However, even though the likelihood of detecting nitrate contamination in the study area is low, potential anthropogenic nitrogen sources must be carefully managed, for it is better to be safe than regretful.
文摘突破厚包气带农田根层氮磷淋溶与地下水污染复杂定量关系和阻控机理是国际研究难点。本文系统梳理了重点研发专项"农田氮磷淋溶损失污染与防控机制"项目取得的主要进展,项目包括以下4方面研究内容:1)北方主要农区农田根层氮磷淋溶时空规律;2)根层-深层包气带氮磷淋溶机制和主控因子;3)黑土、潮土和褐土氮磷淋溶阻控机制及其效果;4)典型农区氮磷淋溶风险与区域消减途径。主要科学发现包括:1)受土地利用类型、地下水埋深、包气带岩性、水文地质条件等综合因素的影响,黑土区、潮土区和褐土区根层氮磷淋溶规律与地下水硝酸盐超标率体现出空间不一致和较大差异性。黑土区虽然根层淋溶较小,然而受地形地貌影响,地下水水质对淋溶响应更强烈,应该进一步研究黑土区地下水水质对淋溶的响应机制。华北潮土区和褐土区厚包气带具有明显氮阻控能力,应该进一步加强厚包气带对氮磷淋溶减排机理与途径研究。2)基于长期施肥定位试验和12 m深观测井对包气带农田土壤氮盈余累积特征和淋失规律的研究发现,华北平原区的环境安全施氮量约为200kg(N)·hm-2·a-1,超过环境安全阈值的多投入氮肥中有51%淋失到1m根层以下,不合理灌溉、强降水、大孔隙和裂隙是造成土壤硝酸盐淋溶的主要因素,对包气带累积硝态氮的淋失作用可影响至6m以下土层。3)利用深层取样和生物学方法结合,对厚包气带0~10.5m原位土壤微生物的反硝化活性和微生物区系组成的研究结果表明,表层土壤是微生物进行反硝化的主要场所,深层土壤中反硝化作用显著减弱,"碳饥饿"是限制底层土壤反硝化微生物丰度与活性的关键因素;室内培养试验证实添加碳源可有效激活土壤微生物的反硝化活性,为"根层截氮包气带脱氮"的淋溶阻控机理找到了突破口。4)利用黑土、潮土和褐土区氮磷淋溶阻控试验、全国农业面源污染国控监测网、北方农区地下水硝酸盐监测网和NUFER (NUtrient flows in Food chains, Environment and Resourcesuse)模型,提出了养分损失脆弱区区划和区域氮磷污染削减草案,可为农业绿色发展和面源污染阻控提供科学依据。
