Soil Nitrates Following Four Years Continuous Corn and as Surveyed in Irrigated Farm Fields of Central and Eastern Colorado

Abstract

High rates of fertilizer N used in many intensive farm management systems have been cited as a potential pollution hazard to surface and ground waters. The purpose of this study was to evaluate soil NO3− accumulations following 4 years continuous corn (Zea mays L.) grown with different nitrogen and irrigation regimes, and to compare these results to present NO3− concentrations found in irrigated farm fields of central and eastern Colorado. Soil NO3− content in the 300‐cm sampled profile was significantly influenced by both fertilizer N and irrigation treatments; the greater accumulations were associated with the two higher fertilizer N rates and two lower irrigation rates. Nitrate increased linearly in relation to fertilizer N between 67 and 269 kg N/ha and could be described by two simple regression equations separating the irrigation treatments into two groups (l‐2 and l‐3, low rates; l‐4 and l‐5, high rates). Coefficients of determination for the two groups were 0.981 and 0.975, respectively. Two hundred and seventy irrigated farm fields were sampled to a depth of 90 cm in central and eastern Colorado. Mean soil NO3−‐N content was 173 kg/ha and contents were not significantly different between coarse and fine textured groupings. Fields sampled immediately following beans (Phaseolus vulgaris L.) contained similar amounts as those following corn. Mean soil NO3− content decreased with greater soil depth. Observed NO3− concentrations appear to be the result of gradual accumulations from annual or near‐annual fertilizer N and/or manure applied over a period of time. Data from the 4‐year corn experiment clearly illustrate that NO3− can accumulate in a soil profile even when fertilizer N is applied at rates below that required for maximum production.

Corn Response to Nitrogen Fertilization in a Soil with High Residual Nitrogen

“…This observation is supported by an adjacent 15 N fertilizer study with onion and corn by Halvorson et al (2002), who found fertilizer N was leached to 180‐cm depth the year of application to an onion crop and was still present after harvest of the following corn crop with no additional fertilizer N applied. Ludwick et al (1976) reported NO 3 –N leached below the rooting depth of irrigated corn with increasing NO 3 –N levels as N fertilizer application rate increased.…”

Effects of Nitrogen Rate, Irrigation Rate, and Plant Population on Corn Yield and Water Use Efficiency

“…I rrigation and fertilization provide effective means to increase crop yield in the Great Plains (Wienhold et al, 1995; Norwood, 2000). However, improper irrigation and fertilization management is also a major contributor to water contamination and water resource shortages (Ludwick et al, 1976; Al‐Kaisi et al, 1997, 1999). Increasing uses of irrigation and fertilization in the Great Plains have raised concern regarding ways of managing water and nutrients (especially N) more efficiently to overcome excessive irrigation and nutrient losses.…”

EFFECT OF DELAYED EMERGENCE ON CORN (ZEA MAYSL.) GRAIN YIELD

“…moisture (Ludwick et al, 1976). Excess N in the soil is also susceptible to loss by other mechanisms such as plant loss as ammonia (NH 3 ), denitrification, surface runoff, leaching and volatilization (Raun and Johnson, 1999) thereby reducing NUE Table 3.…”