Western Ag Innovations discerned a need for a product that would be attractive to researchers who prefer to test out the PRS™-probes before deciding whether or not to use them in their research programs. A simple soil fertility lab module was developed that could be easily inserted into an existing curriculum and would showcase the effectiveness of the PRS™-probes in studying soil nutrient dynamics in situ in a relatively short time. Below is a basic nitrogen mineralization/immobilization study that will familiarize both the researcher and students with the use of the PRS™-probes.

To measure the dynamics of mineralization and immobilization processes in situ using a functional soil testing tool. The PRS™-probes will be used to illustrate the fundamental principle of crop residue management to students as well as familiarize them with an effective alternative soil testing tool.

• Three treatments: control, pea grain (C:N of 11:1), and cereal straw (C:N of 85:1).
• The PRS™-probe burial times are 1h (“Start”), and one week.
• Add deionized water to bring the soil to field capacity.
• Insert four PRS™-probes (two cation- and anion-exchange probes) into the soil, ensuring complete coverage of the ion-exchange resin membrane (Figure 1a and 1b).

• After 1h, remove the PRS™-probes from the “Start” bag, in order to determine the initial (i.e., time = 0) soil N supply rate of your soil. Clean the PRS™-probes and store them in a fridge until the following lab period.
• Insert fresh cation- and anion-exchange PRS™-probes into the same slots in the soil (Figure 1b), squeeze the bag to ensure good contact between the soil and membrane, and then reseal the bag.
• After one week, remove the PRS™-probes and discard soil bag.

• Pull the PRS™-probes from the soil and immediately wash off ALL residual material by spraying with deionized water (distilled water should provide reasonable accuracy).
• Gently scrubbing the adhering soil with a brush while washing may be necessary to remove sticky clay soil (Figure 2).

Figure 2. Thorough scrubbing/washing of PRS™-probes following removal from soil.

• Elute the probes by adding the appropriate amount of 0.5N HCl (Figure 3).
• Remove the PRS™-probes from the elution bag and store in Ziploc® bag for analysis.

Figure 3. PRS™-probe elution using 0.5 N HCl.

• The data generated with the PRS™-probe is unlike data generated from a conventional soil extraction for nutrient concentrations. It is a dynamic flux measure of nutrient supply rate, based on sorption to a specific surface area, and changes in response to changing soil conditions.

Figure 4. Nitrogen supply rates of wheat straw
and pea grain treatments after one week.