Groundwater recharge under compacted agriculturalsoils, pineand prairie in Central Wisconsin, USA

A M Radatz,A E Hartemink,B Lowery,W L Bland

doi:10.31285/agro.16.675

Abstract

The water table in Wisconsin Central Sand Plain (CSP) dropped 1.8 m between 2002 and 2010, and several lakes in the area suffer from low water levels. The lower groundwater level has been attributed to agricultural cropping practices, specifically irrigation, and a reduction in ground-water recharge. Dominant soils in this area are sands (Udipsamments). The objective of our research was to quantify groundwater recharge under (i) irrigated agricultural crops, (ii) prairie, and (iii) a 50-year old pine tree plantation in the CSP. Equipment was installed at five sites to monitor water table elevation, soil water content, and precipitation at 15-minute intervals. It was found that, when the soil was at field moisture capacity, precipitation during the growing season resulted in 1.4 cm more water table rise under a prairie than under irrigated agricultural fields. Agricultural crops used groundwater through irrigation, but natural vegetation relied on soil available water, and capillary rise of water from the shallow groundwater table (1 to 2 m to water table), for daily transpiration. After snowmelt, prairie vegetation yielded greater rise, up to 16 cm, in the water table than agricultural fields. Lack of crop residue on the soil surface of agricultural fields resulted in a continuous layer of frost in the soil profile that extended to about a meter depth. This thick, frozen layer was enhanced by greater soil compaction under irrigated crops compared to limited or no compaction in prairie areas. The key finding was that this deep frost in the soil profile inhibited snowmelt water from infiltrating and recharging the groundwater. Thus, compacted-irrigated agricultural soils in the CSP alter groundwater recharge characteristics during frozen and non-frozen ground periods. Increased crop residues on the surface of agricultural fields might enhance groundwater recharge during winter snow melt periods.

Highlights

Much of the original tall-grass prairie land cover in the United States of America (USA) and the State of Wisconsin has been converted to agricultural crops
The objectives of this study were to compare the differences between year-long soil water and groundwater recharge under prairie vegetation, pine trees, and irrigated agricultural crops in the Central Sand Plain (CSP)
Effects of surface cover on water table recharge during the growing season The water table under the mixed prairie and corn crop responded comparably to recharge events during the 2008 growing season, but the water table elevation under pine plantation increased only after 50 mm of precipitation (Fig. 1)

Summary

Introduction

Much of the original tall-grass prairie land cover in the United States of America (USA) and the State of Wisconsin has been converted to agricultural crops. Weisenberger [3] found conversion from tall-grass prairie to row crops results in increased soil compaction. The vegetation affects water infiltration by interception of precipitation, which later evaporates rather than infiltrate and recharge soil water or groundwater. This is different for different vegetation types. With greater amounts of precipitation intercepted by plant canopies and residue on the soil surface, less water is available to infiltrate into the soil and recharge groundwater [6]. Soil temperature remains significantly greater when there is at least 90% vegetative cover on the surface than a bare soil surface [7], and this will impact water recharge. Genxu et al [8] reported that freeze-thaw processes can be significantly affected by changes in vegetative cover

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Conclusion