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Microwave Radiation and Incubation Effects on Resin-Extractable Nutrients: II. Potassium, Calcium, Magnesium, and Phosphorus

Dep. of Plant and Soil Science, Montana State Univ., Bozeman, MT 59717

*Corresponding author.

ABSTRACT

The phytoavailability soil test (PST) is a resin-extraction methodology being developed for use on fresh soil samples. Mineralization or other nutrient conversions during shipment of samples to a soil-testing laboratory are of concern with this soil-test approach. The objective of this research was to investigate microwave-radiation (MWR) treatment of soil samples to arrest microbial conversions of nutrients during incubation of fresh samples. Fresh samples from three Ap horizons of Montana soils (Haploborolls) were subjected to MWR for 0 to 4 min and then incubated at 20 °C for 0 to 12 d. Subsamples were also dried before being subjected to the same treatments. Nutrients were extracted with mixed-bed ion-exchange resin extractors placed in saturated pastes of each sample. Standard soil tests were also conducted on dried soil samples. Results for K, Ca, and Mg indicate increased resin extractability with increasing MWR, and incubation without MWR caused both increases and decreases in extractability, depending on length of incubation. Neither MWR nor incubation resulted in consistent changes in resin-extractable P. Results from dried soil were generally similar, except one soil did not produce significant changes in resin-extractable cations due to MWR or incubation. Extractable cations by standard soil tests were not influenced by MWR, but P levels increased with length of MWR. These results support those for N and S, providing additional evidence that MWR should not be recommended for soil samples intended for soil testing by either standard or PST methods.

Contribution no. J-2439 from Montana Agric. Exp. Stn.

Received for publication January 12, 1990.