Testing Soils and Cornstalks to Evaluate Nitrogen Management on the Watershed Scale

Abstract

High nitrate (NO3-N) concentrations in Iowa rivers have been linked to areas of intensive row crop production, but they have not been experimentally linked to specific management practices used during row crop production. This study demonstrates how the late-spring test for soil NO3-N and the end-of-season test for cornstalk NO3-N can be used to measure N sufficiency levels across many fields and how the results can be used to evaluate management practices within a watershed. More than 3200 soil and cornstalk samples were collected over a 12-yr period from fields planted to corn (Zea mays L.) and already fertilized by farmers using their normal practices. Results showed that early-season rainfall and associated N losses were major factors affecting N concentrations in soils and cornstalks. Evidence for NO3-N movement from fields to rivers was provided by an inverse relationship between annual means for NO3-N concentrations in soils and rivers. Because these losses can be avoided by delaying N applications, the practice of applying N several weeks or months before plants grow was linked to inefficient use of fertilizer and manure N by crops. Results of the study demonstrate how aggregate analyses of soil and cornstalk samples collected across many farms and years make it possible to identify the major factors affecting N management outcomes and, therefore, N management practices that are likely to produce the best outcomes within a watershed or region. This approach seems to have unique potential to interrelate the management practices of farmers, the efficiency of N fertilization, and NO3-N concentrations in rivers.

Weather whiplash in agricultural regions drives deterioration of water quality

“…Climate change is predicted to increase the frequency and severity of growing-season drought (Dai 2012;Hatfield et al 2013) and produce more extreme precipitation in the spring (Kunkel et al 1999;Hatfield et al 2013) (defined as [ 30 mm in 24 h). Drought reduces agricultural crop yield (e.g., a 24% reduction of the U.S. maize harvest in 2012, Al-Kaisi et al 2013) and enriches soil nitrate concentrations (Balkcom et al 2003). We focus on the 2012-2013 Midwestern U.S. drought as a ''natural experiment'' to understand how changing climate may alter N loading to streams and rivers.…”

Probability of profitable yield response to nitrification inhibitor used with liquid swine manure on corn

“…As a result, relatively high nitrification rates in the fall can cause large losses of nitrified NH 4 (i.e. NO 3 leaching) applied with manure after excessive spring or early summer rainfall events (Balkcom et al 2003;Hansen et al 2004). To reduce spring NO 3 losses from leaching and denitrification, NI might be used with fallinjected LSM (McCormick et al 1983;Calderón et al 2005).…”

Soil‐Test Biological Activity with the Flush of CO2: I. C and N Characteristics of Soils in Corn Production

“…Insufficient N leads to low biomass production as a result of limited protein synthesis and low photosynthetic activity, all of which causes cascading negative effects on water-use efficiency, biological activity, ecosystem functioning, economic return from farm capital investment, and social welfare of farming communities (Smil, 2002;Tilman et al, 2011). In contrast, excessive N leads to susceptibility of crops to invasion by pests, leakage of N from the soil and plant systems to the environment causing air and water pollution, and loss of investment from costly inorganic N inputs (Vitousek et al, 1997;Hatfield and Follett, 2008).Nitrogen availability in soils has been investigated for decades (Waksman and Starkey, 1924;Fribourg and Bartholomew, 1956;Stanford, 1968;Jenkinson and Powlson, 1976;Jansson and Persson, 1982;Campbell et al, 1991), yet reliable predictions of N fertilizer application rate to optimize cereal grain yields have been elusive (Balkcom et al, 2003). Early investigations to optimize inorganic N inputs focused on defining potentially mineralizable N from a nonlinear function derived from inorganic N released through successive leaching and incubation (Stanford and Smith, 1972).…”

“…Nitrogen availability in soils has been investigated for decades (Waksman and Starkey, 1924;Fribourg and Bartholomew, 1956;Stanford, 1968;Jenkinson and Powlson, 1976;Jansson and Persson, 1982;Campbell et al, 1991), yet reliable predictions of N fertilizer application rate to optimize cereal grain yields have been elusive (Balkcom et al, 2003). Early investigations to optimize inorganic N inputs focused on defining potentially mineralizable N from a nonlinear function derived from inorganic N released through successive leaching and incubation (Stanford and Smith, 1972).…”