Skip to main content
ARS Home » Plains Area » Temple, Texas » Grassland Soil and Water Research Laboratory » Research » Publications at this Location » Publication #333005

Title: Evaluation of H3A for determination of plant available P vs. FeAIO strips

item Haney, Richard
item HANEY, ELIZABETH - Texas Agrilife Research
item Harmel, Daren
item Smith, Douglas
item White, Michael

Submitted to: Open Journal of Soil Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/5/2016
Publication Date: 11/8/2016
Publication URL:
Citation: Haney, R.L., Haney, E.B., Harmel, R.D., Smith, D.R., White, M.J. 2016. Evaluation of H3A for determination of plant available P vs. FeAIO strips. Open Journal of Soil Science. 6:175-187. doi:10.4236/ojss.2016.611017.

Interpretive Summary: Soil testing is used to determine the amount of fertilizer to apply to a given crop. In order to determine the amount of fertilizer to apply requires soil to be mixed with chemical solutions to separate the nutrients of interest from other ingredients in the soil. Traditionally, this has been accomplished with chemicals solutions from the 1950s. We have developed chemical solutions that mimic nature, or the chemistry that occurs in the field under a growing plant. Soil testing labs lack a reliable estimate of “plant available” nutrients namely ammonium-N, nitrate-N, phosphate-P and potassium-K. H3A-3 is a modification of an original soil extractant that mimics the plant roots’ natural process for acquiring nutrients. Plants leak organic acids out of their roots, which temporarily lowers the soil pH and makes nutrients more easily accessible. H3A-3 uses these same naturally occurring organic acids in an extractant that can be used in soil testing labs. The modifications from H3A-2 were to reduce some of the ingredients. H3A-3 is inexpensive, non-toxic and reliable since it uses the same method to get nutrients as the plant.

Technical Abstract: Phosphorus is an essential nutrient for plant growth but in excess is a source of environmental pollution. Fertilizer additions of P are recommended based on soil tests; however, the commonly applied P extractants are often applied outside of their design criteria (specifically soil pH). As a result, soil tests can produce inaccurate estimates of plant available P in the soil, which either increases P loss in runoff contributing to eutrophication or decreases crop production contributing to economic loss. In this study, 200 diverse soils from across the US were extracted with Mehlich 3, water, H3A-3, and FeAlO strips. Comparison with FeAlO was critical, as this method is accepted as the “gold standard” for plant-available P, but it is rarely used in commercial labs because of time and financial constraints. H3A-3 produced mean, median, standard deviations that are very similar to FeAlO strip results and low relative errors (< 10%), as well as highly correlated regression relationships (r2 > 0.96 with slopes 0.95-0.98). Although Mehlich 3 and water were correlated with FeAlO, Mehlich 3 (strongly acidic) extracted much more P than FeAlO, and water (low buffering capacity) extracted much less P across the range of soil pH values. Thus, H3A-3 provides an improved methodology to accurately determine plant-available P by mimicking root exudate action in the soil, while avoiding the time-consuming and costly FeAlO procedure. In the face of high-profile water quality impairments with enormous economic costs, such advancements are critical to balance agronomic production with environmental concerns.