Submitted to: Communications in Soil Science and Plant Analysis
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 2/22/2010
Publication Date: 6/25/2010
Citation: Haney, R.L., Haney, E.B., Hossner, L.R., Arnold, J.G. 2010. Modifications to the new soil extractant H3A-1: A multinutrient extractant. Communications in Soil Science and Plant Analysis. 41(12):1513-1523.
Interpretive Summary: Soil testing labs lack a reliable estimate of “plant available” nutrients namely ammonium-N, nitrate-N, phosphate-P and potassium-K. H3A-2 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-2 uses these same naturally occurring organic acids in an extractant that can be used in soil testing labs. The modifications were to reduce the soil shaking time from 30 min. to 5 min. and reduce the pH of the extractant by roughly 1 pH unit (from 5.3 to 4.4). H3A-2 is inexpensive, non-toxic and reliable since it uses the same method to get nutrients as the plant.
Technical Abstract: A new soil extractant (H3A-1) with the ability to extract NH4-N, NO3-N, and P from soil was originally developed and tested against 32 soils, which varied greatly in clay content, organic C, and soil pH (Haney et al. 2006). The use of H3A eliminates the need for multiple soil extractants when analyzing for inorganic N (NH4-N, NO3-N, and NO2-N) and P (ortho or elemental) as well as the use of separate soil P extractants for acid and calcareous soils. The new extractant also maintains the soil extract pH, on average, within 1.5 units of the soil pH. H3A-1 is composed of organic acid root exudates which are naturally occurring and lithium citrate. In this study, H3A-1 was modified to increase the clarity of the supernatant and improve the nutrient extracting relationships with other well-known soil extractants. Modifications to the extractant include eliminating the use of EDTA and DTPA. The shaking time was also reduced from 30 min to 5 min. Correlations show improved relationships with NO3, NH4, PO4, P, K, Ca and Zn when compared to the original H3A-1 as well as standard soil test methods (Olsen, KCl, water, Mehlich 3, Bray 1, ammonium acetate and DTPA). The modifications were tested on 60 soils, varying in pH, organic C, and clay content, collected from the NAPT (North American Proficiency Testing) program.