PRS Technology

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When burying PRS® Probes in the field, it is important to account for the effects of soil temperature on ion diffusion and microbial activity (i.e., mineralization and immobilization). At lower soil temperatures, ion diffusion in soil is slower and, therefore, nutrient movement to the PRS® Probes will be reduced. This is reflected in the smaller nutrient supply rates measured in the same soil at 4°C compared to 20°C (Table 1).

Table 1. Mean (n=3) nutrient supply rates measured at varying soil temperatures during one-hour PRS® Probe burial. (Unpublished data; P< 0.05)

  Nutrient Supply Rate (μg/10cm²/hour)
Soil Temperature (°C) NO3--N + NH4+-N PO4-P K SO4-S
4 63 b 2.3 b 217 c 17 c
10 74 ab 2.7 ab 248 bc 21 b
20 86 a 3.0 a 275 ab 25 a
30 90 a 3.0 a 292 a 25 a

Although greater differences likely will occur following longer burials (i.e., 24 h vs. 4 weeks), even short-term burials indicate an effect of soil temperature on nutrient ion movement to the PRS® Probe (Table 1). Similarly, microbial activity (i.e., mineralization) will be reduced at lower soil temperatures, which will be reflected in the nutrient supply rates for those nutrients governed by such process (i.e., N and S but not P and K; Tables 1 and 2). Therefore, it is prudent to account for soil temperature differences among treatment plots when using PRS® Probes, which will help to delineate between direct treatment effects and indirect temperature effects on the measured nutrient supply rates.

Table 2. Mean (n=3) nutrient supply rates and microbial activity of a loamy sand soil (O.M. = 1.8 %) incubated for one week at varying soil temperatures. (Unpublished data; P < 0.05)

Soil Temperature N Supply Rate P Supply Rate Cumulative Respiration
(°C) (μg/10cm²/week) (μg CO2-C/kg oven dry soil)
5 62 b 2.2 a 37 c
23 90 b 2.1 a 189 b
32 300 a 2.4 a 337 a