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Notes

• Use shorter burial periods for moist, fertile soils.
• Shorter or longer burial periods may be required, depending on objectives and soil conditions.
• Preliminary experiments are valuable to determine optimal burial periods.
• A consistent burial period is required to reliably compare treatment effects on soil nutrient supply due to non-linear adsorption of nutrients by PRS® probes.

Actual Example

Nutrient supply to PRS® probes following oats or clover determined with eight one-week burial periods vs. one eight-week burial period (Salisbury, 2000).

Notes

• One- week burials were deployed sequentially (same slots).  Measurements are expressed per burial period (per one week or per eight weeks).
• Compared to one-week burial, eight-week burial period measurements were 3-fold greater (NO₃-N), 40-90% greater (P, Ca and Mg) or the same (NH₄-N, K).
• Thus, soil nutrient supply was not linear for any of these nutrients: eight-week burial measurements were not eight times higher than one-week burials.
• Relative differences between treatments were consistent among burial treatments for all nutrients except NO₃-N, which was 56% greater following clover than oat based on one-week burials, but 33% greater based on the eight-week burial.
• Nitrogen uptake by winter wheat over eight-week period was 58% greater following clover than oat.
• Weekly measurements for NO₃-N tended to decrease with time and were most strongly affected by preceding crop during initial few weeks.
• Eight-week measurements were similar to maximum weekly measurements for Ca, Mg and P.
• Eight-week measurements were similar to measurements over final few weeks for NH₄-N and K.

Considerations

• Macro-nutrient supply rates can be determined in moist soils using burial periods of as little as one hour.
• Most research has utilized burial periods of one to eight weeks. This period is sufficient to ensure that impacts of disturbance due to installation are minimal and provides a sensitive indicator of soil nutrient activity.
• As nutrients are only mobile in moist soils, burial periods in dry environments should include at least one period of significant precipitation.
• PRS® probes can also be deployed overwinter, but nutrient adsorption will only occur during periods when soils are unfrozen.
• NO₃-N increases with burial duration unless there is strong competition from plants.
  
  • Studies evaluating soil N mineralization in the presence of plants often install probes within root-enclosure cylinders (RECs) to prevent plant uptake.  Sequential burial in RECs for periods of one to four weeks is used to evaluate seasonal differences in soil N mineralization.
  • Without use of RECs, burial of PRS® probes for one to four weeks prior to the period of rapid plant uptake is often useful to evaluate treatment differences in soil N supply.
  • Long-term burials in the presence of plants often provide a sensitive indicator of soil N fertility, but underestimates total soil N supply to plants.
  • Burial periods should not exceed the adsorption capacity of PRS® probes: the maximum adsorption for NO₃-N is 2100 mg N/m² of membrane, but should not exceed <1000 mg N/m².  This is only an issue in heavily fertilized soils (see interpretation).
• Nutrients other than NO₃-N are less sensitive to use of RECs or burial period.
• Nutrients that are strongly held by PRS® probes (e.g., Ca, Mg, Fe) are stable or increase with time.  Measurements from long-term burials reflect periods of maximum nutrient activity.
• Nutrients that are weakly held by PRS® probes are dynamic.  Measurements from long-term burials primarily reflect nutrient activity prior to retrieval.