Agricultural Chemical Movement through a Field-Size Watershed in Iowa:  Surface Hydrology and Nitrate Losses in Discharge

Abstract

Nonpoint source pollution of surface water by nitrate from agricultural activities is a national problem. An agricultural watershed in the Iowa Loess Hills with a 23year history of annual corn production with average N fertilization is studied. Headcut seepage is transported through a natural riparian zone and observed as weir baseflow; surface runoff is measured separately. Nitrate runoff graphs illustrate the importance of high-frequency sampling of each event to permit quantitative estimation of chemical loss. The concentration of nitrate carried from the field in basin drainage steadily increased from <1 mg L -1 in 1969 to >20 mg L -1 in 1991. The rate of cumulative increase in the amount of applied N is greater than the rate of removal by the crop. Over the 23-year record, 23% of the mean annual application of N remains stored and available for leaching or chemical conversion by soil microbes. Nitrate removal during early spring snowmelt surface runoff shows a diurnal pattern that corresponds to the daily freezing and thawing of the surface soil in early March. Contribution to the load of nitrate deposited on the soil surface by rainfall is very small in comparison to the amount applied by fertilizer application. Measurable changes in water quality within various hydrogeologic compartments are seldom observed in just a few years of monitoring. Therefore, these results emphasize the importance of long-term data sets incorporating temporal variability when evaluating the impact of agricultural practices on surface water resources.

Subsurface lateral flow from hillslope and its contribution to nitrate loading in streams through an agricultural catchment during subtropical rainstorm events

“…These relationships have been widely reported in the literature (Holz, 2010;Nadal-Romero et al, 2008;Williams, 1989), but explained variously (e.g. Steinheimer et al, 1998;Seeger et al, 2004;Holz, 2010). The dominance of particulate N and P in total N and P (over 90 % and about 100 % respectively) suggests that overland flow controlled the delivery of particulate nutrients together with suspended sediments from the hillslope to the trenched stream.…”

“…Excess N fertilizers can be transformed into NO − 3 -N and leached into deep soil (Vazquez et al, 2006). If NO − 3 -N in the deep soil can not be promptly used by plants due to limited root depth, it will be intercepted and transported into streams by subsurface lateral flow (Steinheimer et al, 1998;Royer et al, 2006). This will then result in larger-scale water quality issues.…”

Responsive in-season nitrogen management for cereals

“…In the U.S. for example, the amount of biologically reactive N delivered from the land to coastal waters has increased noticeably over the past century (Turner and Rabalais, 1991), and has been proposed as a primary causal factor in oxygen depletion of coastal waters (Rabalais, 2002). Current fertilizer N management practices in the U.S. Corn Belt, especially when N fertilizer is applied at rates greater than crop needs (Burwell et al, 1976), have lead to nitrate-N being a major contaminant found in the surface and ground waters of the region (Schilling, 2002;Steinheimer et al, 1998;CAST, 1999). In summary, current N management strategies for cereal production systems in the U.S. and around the world are characterized by low N use efficiency (NUE), environmental contamination, and considerable ongoing public debate regarding use of N fertilizers in crop production.…”

Aplicación de un modelo de calidad de agua y definición de criterios para el monitoreo de un fertilizante en una cuenca rural

“…Aquí, se observa que la carga de nitratos aumenta con el escurrimiento superficial, este resultado es semejante al obtenido por Steinheimer et al (1998) y Varanou et al (2002. Se aplicó un modelo de regresión lineal entre los resultados de los análisis de las muestras de agua de la sección de control del arroyo Tapalqué correspondiente a la subcuenca 5 (Sección A) que ha sido objeto central de este estudio y los obtenidos en otra sección de cierre del arroyo a la cual confluyen las subcuencas 1 a 4 y 6 (Sección B), figura Nº 10.…”

“…Se observa para los eventos de octubre de 2002 que la evolución temporal de la carga de nitratos está asociada linealmente al escurrimiento superficial para una escala de tiempo diaria y el resultado es semejante al obtenido por Steinheimer et al (1998) y Montgomery y Kennedy (1985.…”