Evaluation of Measurement Methods as Surrogates for Tile-Flow Nitrate-N Concentrations

Issue

Nitrogen management practice effects on nitrate loss to surface waters are best determined through measurement of nitrate-N concentrations in tile water flow at specially developed water quality sites. However, these sites are expensive to develop and maintain. In addition, the number of treatments that can be compared is limited due to physical constraints on the number of plots. With a common need to determine N reduction practice effects with multi-year rotations, such as corn following soybean, the number of drainage plots available for different practice evaluation becomes even more limited. Surrogate methods need to be developed that allow evaluation of N management practices that reasonably estimate nitrate-N concentrations comparable to measurement in tile flow drainage. If successful, surrogates could be used on land that is not suitable for tile drainage, but where ground water recharge supplies water (and potential nitrate-N) to surface water systems.

Objective

The objective of this project is to relate two measurement methods as surrogates to tile-flow nitrate-N concentrations, then measure the effects of two N reduction management practices on nitrate-N via the surrogate measures and loss in tile drainage.

Approach

The research will include two surrogate methods, measuring soil nitrate-N and soil solution nitrate-N concentrations. Sampling will be done by probing the soil profile and with suction lysimeters. To make the comparison with tile-flow nitrate-N concentrations, two existing water quality tile drainage sites in Iowa will be used, with two nitrogen management practices. Other on-going data being collected also will be available, such as crop production practices, crop yields, and grain N content.