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ARS Home » Plains Area » Temple, Texas » Grassland Soil and Water Research Laboratory » Research » Publications at this Location » Publication #345545

Title: Removal of lithium citrate from H3A for determination of plant available P

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

Submitted to: Open Journal of Soil Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/10/2017
Publication Date: 11/13/2017
Citation: Haney, R.L., Haney, E.B., Smith, D.R., White, M.J. 2017. Removal of lithium citrate from H3A for determination of plant available P. Open Journal of Soil Science. 7:301-314.

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 developed during 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-4 is a modification of H3A-3 extractant. We have removed the chemical lithium citrate from the solution to make it more in line with naturally occurring root exudates that mimic 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-4 uses these same naturally occurring organic acids in an extractant that can be used in soil testing labs. H3A-4 is inexpensive, non-toxic and reliable since it uses the same method to get nutrients as the plant.

Technical Abstract: The soil extractant, H3A, has undergone several iterations to extract calcium (Ca), iron (Fe), aluminum (Al), potassium (K), phosphorus (P), ammonium (NH4-N) and nitrate (NO3-N) under ambient soil conditions. Few soil extractants currently used by commercial and university soil testing laboratories can perform multi-nutrient extraction without over- or under-estimating at least one nutrient. Soil pH and plant root exudates have a strong influence on nutrient availability and H3A was developed to mimic soil conditions. Lithium citrate was previously used in the H3A formulation, but resulted in a cloudy supernatant in some samples, complicating laboratory analyses. In this study, we removed lithium citrate and compared the nutrients extracted from the modified (H3A-4) to the established (H3A-3) solutions. We found that the new extractant, H3A-4, produced a clear supernatant even in soils with low pH and high iron and aluminum concentrations. H3A-4 accurately predicts plant available nutrients and is a viable choice for commercial and laboratory settings due to its ease of use.