Comparison of Field-Moist and Oven-Dry Soil on Mehlich-3 and Ammonium Acetate Extractable Soil Nutrient Concentrations
Martins, P.O.; Slaton, N.A.; Roberts, T.L.; Norman, R.J.
Soil Science Society of America Journal 79(6): 1792-1803
ISSN/ISBN: 0361-5995 DOI: 10.2136/sssaj2015.03.0094
Drying soil samples has been a standard step in soil processing but is known to influence the amount of extractable K. Our objectives were to evaluate the correlation between field-moist (FM) and oven-dry (OD) soil nutrient concentrations extracted with Mehlich-3 extractant and 1 mol L-1 NH4OAc and how Mehlich-3 extractable nutrient concentrations change from oven drying using loamy-textured soils. The Mehlich-3 and NH4OAc extractable K, Ca, and Mg concentrations were highly correlated (r(2) > 0.95) for both FM and OD soils. The relationship between OD and FM soil-K concentrations for Mehlich-3 and NH4OAc was very similar and highly correlated (r(2) = 0.92). The FM soil-K concentrations were lower than OD soil-K concentrations until an equilibrium was reached at 136 mg K kg(-1) for NH4OAc and 158 mg K kg(-1) for Mehlich-3 after which OD soil-K concentrations were lower than FM soil-K concentrations. Oven drying had minimal effect on Ca concentrations and decreased Mg concentrations for both Mehlich-3 and NH4OAc extractions. Oven drying increased Mehlich-3 P concentrations by 8 to 9 mg P kg(-1) when OD soil concentrations were <50 mg P kg(-1). The Mehlich-3 extractable Na, S, and Zn concentrations from OD and FM soils were similar. The OD soil had greater Mn concentrations and lower Cu concentrations than the FM soil. Among the Mehlich-3 extractable nutrients that are used to make fertilization decisions, K concentration was affected to the greatest magnitude and non-uniformly by oven drying, which requires field research to correlate and calibrate new agronomic recommendations.