Long-Term Agroecosystem Research in the Central Mississippi River Basin: Dissolved Nitrogen and Phosphorus Transport in a High-Runoff-Potential Watershed

Abstract

Long-term monitoring data from agricultural watersheds are needed to determine if efforts to reduce nutrient transport from crop and pasture land have been effective. Goodwater Creek Experimental Watershed (GCEW), located in northeastern Missouri, is a high-runoff-potential watershed dominated by claypan soils. The objectives of this study were to: (i) summarize dissolved NH 4 -N, NO 3 -N, and PO 4 -P flow-weighted concentrations (FWC), daily loads, and yields (unit area loads) in GCEW from 1992 to 2010; (ii) assess time trends and relationships between precipitation, land use, and fertilizer inputs and nutrient transport; and (iii) provide context to the GCEW data by comparisons with other Corn Belt watersheds. Significant declines in annual and quarterly FWCs and yields occurred for all three nutrient species during the study, and the decreases were most evident for NO 3 -N. Substantial decreases in first-and fourthquarter NO 3 -N FWCs and daily loads and modest decreases in first-quarter PO 4 -P daily loads were observed. Declines in NO 3 -N and PO 4 -P transport were attributed to decreased winter wheat (Triticum aestivum L.) and increased corn (Zea mays L.) production that shifted fertilizer application from fall to spring as well as to improved management, such as increased use of incorporation. Regression models and correlation analyses indicated that precipitation, land use, and fertilizer inputs were critical factors controlling transport. Within the Mississippi River Basin, NO 3 -N yields in GCEW were much lower than in tile-drained areas, but PO 4 -P yields were among the highest in the basin. Overall, results demonstrated that reductions in fall-applied fertilizer and improved fertilizer management reduced N and P transport in GCEW.

Nested‐Scale Nutrient Flux in a Mixed‐Land‐Use Urbanizing Watershed

“…Analyses were performed according to standard protocols using a HACH DR 2800 spectrophotometer (HACH Company, Loveland, CO). Tests for differences in observed nutrient concentrations were conducted between gauging sites using Kruskal–Wallis and Dunn's post‐hoc multiple comparison tests (CI = 95%, α = 0.05; (Lerch et al ., )). Regression techniques were used to test for significant relationships between observed nutrient concentrations and land use (CI = 95%, α = 0.05).…”

“…Upland soils are a cherty clay solution residuum corresponding to the Weller–Bardley–Clinkenbeard (CBC) association (Hubbart and Zell, ). Claypan consists of an argillic soil horizon of smectitic mineralogy with clay content of 450–650 g kg −1 formed at 10 to 50 cm depth (Lerch et al ., ) and are characterized by high surface runoff (Sadler et al ., ) with baseflow/surface flow ratios less than 0.25 (Baffaut et al ., ).…”

Lake Nutrient Responses to Integrated Conservation Practices in an Agricultural Watershed

“…The maximum number of nodes allowed was set at 21, with a minimum count of 5 allowed in each node. Forward stepwise regression (FSR) analysis was conducted to examine associations between changes in nutrients (dependent variable) and implemented area (in hectares) of four major BMP types and BMP locations (independent variables) over the 14‐yr monitoring period (Lerch et al, 2015; Tuppad et al, 2010). Forward stepwise regression used percentile data to compute dimensionless standardized regression coefficients.…”

Long-Term Agroecosystem Research in the Central Mississippi River Basin: Introduction, Establishment, and Overview

“…The next four papers (Sadler et al, 2015; Baffaut et al, 2015b; Lerch et al, 2015b, 2015c) document specific data themes of weather, flow, herbicides, and nutrients. The final four papers (Lerch et al, 2015a; Kitchen et al, 2015; Sudduth et al, 2015; Baffaut et al, 2015a) document research that used data described in the first five papers.…”