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Texas A&M AgriLife — Mehlich-3 sufficiency + High Plains research calibration

v1.1 (2026-08-23) · Primary lab method: Texas A&M AgriLife Soil, Water and Forage Testing Laboratory (College Station). Mehlich-3 ICP is the ONLY extractant recognized by Texas AgriLife Extension Service for P, K, Ca, Mg, Na, S, B (https://soiltesting.tamu.edu/laboratory-methods/, Methods and Method References — 9/2012). NO3-N by cadmium reduction; 0-6 inch depth for routine analysis, paired 0-24 inch profile NO3-N strongly recommended (Trostle/Provin 2021, Texas Row Crops Newsletter; Trostle 2023 Soil Testing Principles Part IV). DTPA for Cu/Fe/Mn/Zn. Boron by hot-water ICP (added to routine test 2025). Cotton calibration: Bronson, K., and R. Bowman. 2004. Nutrient management for Texas High Plains Cotton Production. Texas A&M University. Booker, J.D., K.F. Bronson, C.L. Trostle, J.W. Keeling, & A. Malapati. 2007. Nitrogen and phosphorus fertilizer and residual response in cotton-sorghum and cotton-cotton sequences. Agron. J. 99:607-613. SERA-6 Cotton Publication (Crozier/Hardy/Hardy, Sept 2008, https://aesl.ces.uga.edu/sera6/PUB/sera6-cotton-pub.pdf) Table 1 N rates by state + Mehlich-3 P/K critical level summary §VII-VIII. Cotton revision: Bronson update (Cotton Farming + AgriLife Today, 2021) — 40-45 lb N/bale validated, replacing earlier 45-50 lb N/bale rule of thumb. Grain sorghum sample calculation verbatim from Trostle/Provin 2021 Texas Row Crops Newsletter (https://agrilife.org/texasrowcrops/2021/05/06/on-line-calculator-to-get-texas-am-soil-test-recommendations-based-on-other-labs-test-values/). N application rule of thumb (2 lb N/bu sorghum; 2-2.5 lb N/bu wheat) from multiple AgriLife publications.