The inaccessibility and cost of soil testing reduce effectiveness of fertilizer use on small-scale subsistence farms, and inadequate funding promotes adoption of soil tests in developing countries with minimal validation. For example, the Mehlich-I P extraction used extensively in Guatemala may not be suitable for its broad range of soils. At least four alternatives are available but relatively untested [Bray 1, Mehlich III, Olsen and pressurized hot water (PHW)]. Pressurized hot water is simple and inexpensive but is not tested against other extraction methods under variable P or K fertilization. To determine whether PHW-extracted nutrients could be used to predict maize yield, nutrient content or uptake, soil, plant tissue and grain samples were obtained from calibration studies conducted using five rates of P and three rates of K on soils incubated without plants or cropped with maize in greenhouse and field conditions. In the two soils used in the greenhouse study, maize yield, vegetative P concentration and total P uptake were predicted by PHW extractable P (R² = 0.72, 0.75 and 0.90, respectively). In the field experiment, grain yield was not improved by P or K application, but P content of maize leaf tissue related significantly to PHW-extracted P (R² = 0.40) while Mehlich I did not. There were no yield responses to K application, but relationships defined between extractable K for all five K-extraction procedures and soil applied K were similarly significant. Comparing P extraction methods, PHW was as good as or better than Olsen, Bray 1 and Mehlich III for relating soil P extraction to the parameters measured, and these four alternative extraction methods were consistently better than Mehlich I. Mehlich I extraction should be replaced by one of the four alternatives tested, and PHW is the least expensive and most viable for use in Guatemala.