Assessment of beyond-the-field nutrient management practices for agricultural crop systems with subsurface drainage

Abstract

This paper reviews the characteristics, benefits, and drawbacks of agricultural ditches and wetlands, as well as strategies for applying agricultural best management practices (BMPs) at the watershed scale for improving water quality. This synthesis focuses on the Great Lakes Region and the Mississippi River Basin in the United States, and specifically crop production systems in watersheds with subsurface drainage. The USDA Natural Resources Conservation Service (NRCS) has developed conservation practice standards for open channels and wetlands, which mitigate nutrient and sediment loading to surface water bodies from agricultural lands. Practices that use agricultural ditches to improve water quality, such as the two-stage ditch, have emerged in the last two decades and are starting to see a greater application in the region. Using wetlands as water treatment systems has a long history in a range of settings and over the past several decades is seeing more widespread application in agriculture. Water quality and watershed models are increasingly used to develop watershed strategies for reducing nutrient exports with agricultural BMPs. Models are also helpful in evaluating combinations of practices from the farm scale to the watershed scale. Application and limitations of several models commonly used in these regions of the United States are discussed. Finally, successful conservation strategies at the watershed scale must consider the human dimensions of watershed management, and we summarize the literature in this region on farmer perceptions and adoption of practices.

The utilization of edge-of-field monitoring of agricultural runoff in addressing nonpoint source pollution

“…Smith et al (2018) point out the disconnect between large-scale loading estimates and the large percentage adoption of nutrient practices (4Rs), especially for fertilizer rates for row crops in the Maumee River watershed. King et al (2018) used a network of 40 EOFM sites to look at the 4Rs of fertilizer management and was able to provide further insight and refinement to management that will help with reducing dissolved reactive P. Kalcic et al (2018) reviewed some the obstacles associated with using EOFM to identify the sources of nutrient runoff and evaluating progress of conservation strategies at a watershed scale. Baker et al (2018) point out that more multiscale studies need to be conducted to find ways to connect EOFM data to watershed and in-stream water quality data if we are going to better understand the nutrient fate continuum.…”

“…In contrast, agency personnel focus on larger watersheds and/or multiple watershed scales, and often policy makers focus on political rather than hydrological boundaries. Kalcic et al (2018) also provide further information on the issue of scale and cite a study reviewing the USDA-funded Conservation Effects Assessment Project (CEAP), which sought to detect water quality improvements from conservation actions in over a dozen watersheds across the United States (Tomer and Locke 2011; Osmond et al 2012). This work highlighted the difficulty in applying field-scale solutions across a watershed and most importantly, reliably monitoring performance at a watershed scale.…”

“…The 2011 to 2014 plan for the Great Lakes was recently presented to Congress and contains detailed action items and performance measures. Several papers in this issue provide information on the Great Lakes, and specifically, on Lake Erie (Kalcic et al 2018;King et al 2018;Smith et al 2018). While there are many sources of nutrients, studies commissioned with these action plans have estimated that agriculture, in particular intensive livestock and crop production, is a major contributor of nutrients to both the Great Lakes and Gulf of Mexico. Recent model estimates from the Spatially Referenced Regressions on Watershed attributes model (SPARROW) suggest that up to 85% of the phosphorus (P) and nitrogen (N) entering the Gulf of Mexico originates from agriculture (Alexander et al 2008).…”

“…Often spatially explicit land use and land cover data within a watershed is empirically regressed with in-waterbody flow-weighted nutrient concentrations to define a category of source such as urban, agriculture, or point sources (Haggard 2010;Veith et al 2015). Kalcic et al (2018) provide an excellent synthesis of the limitations of watershed models such as the Soil and Water Assessment Tool (SWAT) and Agricultural Policy Environmental EXtender (APEX), which attempt to relate land use to EOF water quality. Kalcic et al (2018) also point out that differences in geographical scale in defining a water quality issue, and the scale at which the solution should be applied or defined, can create disconnects in determining progress toward a stated goal.…”

“…Kalcic et al (2018) provide an excellent synthesis of the limitations of watershed models such as the Soil and Water Assessment Tool (SWAT) and Agricultural Policy Environmental EXtender (APEX), which attempt to relate land use to EOF water quality. Kalcic et al (2018) also point out that differences in geographical scale in defining a water quality issue, and the scale at which the solution should be applied or defined, can create disconnects in determining progress toward a stated goal. Agricultural producers often focus on the field or farm scale where they make management decisions.…”