Calibrated Passive Sampling - Multi-plot Field Measurements of NH₃ Emissions with a Combination of Dynamic Tube Method and Passive Samplers

The overall goal of this simple field in situ method is to quantify ammonia emissions from replicate plots in multi-plot field trials, facilitating statistical testing and identification of treatment effects. This method can help to answer key questions in the agronomic and agroecological field such as ammonia emmission quantification and abatement, determination of fertilizer use efficiency, and environmental assessment. The main advantage of this method is that it allows in situ quantification of ammonia emmisions in multi-plot field trials independent of electrical power supply.

I will be demonstrating this procedure with Christian Wagner, a master's student from my laboratory. Use comparatively large plots as compared to the sizes usually applied in replicated field trials to avoid effects of uneven fertilizer distribution on ammonia emissions. Use square plot shapes to avoid effects of shifting wind directions on ammonia uptake by the samplers.

Reduce drift of ammonia from one plot to the other by keeping a buffer area of one plot size between plots. Select two treatment plots and one control plot for simultaneous measurement with the dynamic tube method or DTM and passive sampler. Choose treatment plots with punitively high emissions giving a strong measurement signal.

Following preparations as detailed in the text protocol, control measurement is made with the DTM on unfertilized control plots at the beginning and the end of each measurement date following a control, treatment, control sequence. Measure over three to six days to obtain reliable ammonia loss measurements for the timespan of a whole day by accounting for changing emissions due to varying temperatures and wind speeds. Make measurements at early morning, late morning, early afternoon, late afternoon, and shortly before sunset.

To perform measurement, first rinse the DTM system with ammonia-free air by lifting the chambers to a height of about one meter above ground. Then, pump air through the polytetrafluoroethylene or PTFE tubing and chambers with a hand pump directly connected to the terminal PTFE tube of the chamber system. Press the DTM chambers directly into the ground to a depth of about 15 millimeters as marked by a rim at the chamber bottom.

Alternatively, press the DTM chambers into soil rings. Make sure soil clods do not get lodged in between the soil ring and the chamber. Perform the first 20 preparatory pump strokes with a used low-concentration indicator tube to create quasi steady state conditions.

Ammonia concentrations are indicated by a color change of the pH sensitive granules inside the tube, from dark yellow to bluish purple and can be read as long as the color change is within a scale printed on the tube. Choose the concentration range of the new indicator tube to be applied in the next measurement based on the information obtained from the observed color change of the used tube. Open a new indicator tube at both ends by breaking the heads off with the tube breaker installed on the pump case.

Insert the indicator tube between the terminal PTFE tubing and the pump by pressing the tube ends into the PTFE tubing and the pump mouth. Insert the tube end with the lowest value on the scale printed on the tube into the PTFE tube and the end with the highest value into the pump mouth. Start pumping up to the default stroke number by pressing the OK button of the automatic pump or compressing the hand pump.

Keep the pause between prepumping with the used tube and beginning of the actual measurement as short as possible. If a hand pump is used for measurements start the stopwatch simultaneously with the first stroke of the hand pump. Terminate the measurement when the standard stroke number is reached and the hand pump is fully relaxed.

With relaxation of the hand pump after the terminal stroke is reached, terminate stopwatch measurement. Increase stroke number to a maximum of 50 strokes if the first line indication of the lowest value of the scale printed on the tube is not reached after the standard stroke number. After termination of the pumping use indicator tube readings only when at least the first line on the scale of an indicator tube is reached.

Read the farthest color change on the tube from all sides as the line of coloring is often slightly slanted or uneven and record concentration value. Note the plot, date, time of measurement, number of strokes, and reading in PPM on the record sheet. Clean the rim of the chambers from sticking soil, manure, or fertilizer components with a clean paper towel.

Then, lift the DTM system from the ground and flush as before. Make several measurements at different locations within a plot to increase the reliability of the measurements. Place passive samplers fastened to the steel rods in the center of the experimental plot at 0.15 meter height above the soil or canopy surface immediately after application of fertilizer to a plot.

Hurry with the slurry fertilizer application tractor or system to install the sampler without delay. In case of dry soil, insert the steel rod into the soil with a hammer. Following placement of the passive samplers, walk to the passive sampler with a subdivided tray or bag with sorted filled acid vials for the first sampling interval.

Put on gloves before handling the vials with acid solution. Take out the vial for the respective plot and sampling interval. Unscrew the bottle of the passive sampler and pour the 0.05 molar sulfuric acid solution from the vial into the mouth of the bottle.

Then, screw the lid of the vial back on and return it to the tray or bag. To exchange the 0.05 molar sulfuric acid solution in a passive sampler after completion of a sampling interval carefully unscrew the passive sampler and cautiously route the solution between the windows through the discharge hole into the empty original vial. Refill the sampler through the bottle mouth with a new 0.05 molar sulfuric acid solution from the subsequent unused vial.

Screw the lids on both vials with correct labeling. Fix the passive sampler to the rod by screwing it on the lid connected to the steel rod. Note plot number and filling time on the record sheet.

Calculate the ammonia flexes as described in the text protocol. The results of a field trial for testing the effects of several methods to reduce ammonia emissions after application of cattle slurry compared to application with trail hoses is shown iIncluding incorporation with a rotary tiller, incorporation of acidified slurry, and closed slot injection. The method yielded highly significant differences between ammonia emissions with strongest loss reductions by application with closed slot injection or acidification with subsequent incorporation.

These plots depict the differences between cumulative ammonia emissions after application of different urea fertilizers with and without addition of urease and nitrification inhibitors. Ammonia emission were strongly reduced by use of urease inhibitors independent of the use of nitrification inhibitors. Urea-only combined with nitrification inhibitors showed the highest emissions.

The demonstrated method captures the strong effects of weather conditions on ammonia emissions from urea fertilizers and calcium ammonia nitrate as reflected in varying time courses and emissions levels at different application dates. Low temperatures and rainfall strongly reduce the emissions while high temperatures increased relative losses and the velocity. The effect of varying ammonia emissions on winter wheat grain nitrogen uptake, which can only be demonstrated in multi-plot field trials, is shown.

Grain nitrogen uptake linearly decreased with ammonia emissions. Following this procedure also allows you to apply other methods like greenhouse gas, chamber measurements, soil sampling, plant sampling to determine agronomic efficiency and overall environmental sustainability. Thank you for watching this video and I wish you success in applying the proposed method.