IMPACTS OF AGRICULTURAL DRAINAGE WELL CLOSURE ON CROP PRODUCTION: A WATERSHED CASE STUDY1

Abstract

ABSTRACT: Much of north‐central Iowa is characterized by flat topography, shallow depressions, and poor natural surface drainage. Land drainage systems comprising of tile drains and agricultural drainage wells (ADWs) are used as outlets for subsurface drainage of cropland under corn and soybean production. Studies have shown that these drainage systems, mainly the ADWs, are potential routes for agricultural chemicals to underground aquifers. To protect the region's vital groundwater resource, researchers are evaluating alternative outlets ranging from complete closure of existing ADWs (and creation of wetlands) to continued use of ADWs and chemical management in a comprehensive policy framework.This paper presents the results of a study designed to provide government jurisdictions, farmers, and land managers information for assessing the impact of closing ADWs on crop production. The study couples a geographic information systems database for a 471‐hectare watershed in Humboldt County, Iowa, with a groundwater flow model (MODFLOW) and an empirical crop yield loss model to predict long‐term effects of complete closure of ADWs on crop production. The cropland areas inundated and the relative crop yield loss due to ADW closure are determined as a function of long‐term climatic data. The results indicate that elimination of drainage outlets in the watershed could result in ponding of low‐lying areas and poorly drained soils, making them unsuitable for crop production. Such wetness also decreases the efficiency of production in the no‐ponding areas by isolating fields, and the crop yield loss can be reduced by an annual average of about 18 percent.