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ARS Home » Midwest Area » Ames, Iowa » National Laboratory for Agriculture and The Environment » Soil, Water & Air Resources Research » Research » Research Project #432220

Research Project: Nitrification Benchtop Experiment Summary: SOP Study

Location: Soil, Water & Air Resources Research

Project Number: 5030-11610-005-72-T
Project Type: Trust Fund Cooperative Agreement

Start Date: May 1, 2017
End Date: Dec 31, 2018

Objective:
Develop and demonstrate a methodology for replicable continuous-flow laboratory column studies with intact soil cores: 1) Integrate soil nitrate sensors for within-column monitoring of the soil water solution; and 2) Generate NO3- and NH4+ data for improving a nitrogen advisor model.

Approach:
The experiment would utilize a soil column with a continuous unsaturated flow of water pumped through the column. This experiment is focused on working through the soil column sampling, setup, and design, and would involve 2 phases: 1) Soil core sampling, setup and design. In this phase, many of the design details could be tested and modified, as needed, until intact soil cores can be taken from the field, transported to the lab and inserted into the continuous flow column. Success will be based on the ability to repeatedly construct an intact continuous flow column that exhibits minimal preferential flow. Some key details to address in this phase are minimizing core disturbance during sampling, dimensions of the soil core, avoiding artificial preferential flow (especially at the point of column lining-soil core contact), and sensor placement and flow effects. Samples for microbial immediately before column setup to determine if changes in the nitrifier abundance occurred during between sampling and the start of the experiment. Key chemical properties (NH 4+ , NO 3- , pH) should also be taken at these times; and 2) Nitrogen Pulses. After phase 1 is complete, columns would be constructed and used for nitrogen pulse experiments. Once steady-state flow is established in the column, a pulse of NH 4 + would be introduced into the column. Sampling ports would be located along the column to allow sampling of NH 3+ and NO 3- concentration in soil solution throughout the study using vacuum extraction. Nitrate sensors would be located close to these ports so that measurements could be compared to sensor readings. Concentration of NH 3+ and NO 3- in the effluent would also be measured frequently. The experiment would end when NO 3- levels in the effluent are close to prepulse levels, which could take 2-3 weeks, but will depend highly on soil properties, flow rate ,and soil temperature. This phase would first focus on repeatability of N measurements and quantifying variability between soil cores.