Soil and Surface Runoff Phosphorus Relationships for Five Typical USA Midwest Soils

Abstract

Excessively high soil P can increase P loss with surface runoff. This study used indoor rainfall simulations to characterize soil and runoff P relationships for five Midwest soils (Argiudoll, Calciaquaoll, Hapludalf, and two Hapludolls). Topsoil (15-cm depth, 241–289 g clay kg⁻¹ and pH 6.0–8.0) was incubated with five NH₄H₂PO₄ rates (0–600 mg P kg⁻¹) for 30 d. Total soil P (TPS) and soil-test P (STP) measured with Bray-P₁ (BP), Mehlich-3 (M3P), Olsen (OP), Fe-oxide-impregnated paper (FeP), and water (WP) tests were 370 to 1360, 3 to 530, 10 to 675, 4 to 640, 7 to 507, and 2 to 568 mg P kg⁻¹, respectively. Degree of soil P saturation (DPS) was estimated by indices based on P sorption index (PSI) and STP (DPS_STP) and P, Fe, and Al extracted by ammonium oxalate (DPS_ox) or Mehlich-3 (DPS_M3). Soil was packed to 1.1 g cm⁻³ bulk density in triplicate boxes set at 4% slope. Surface runoff was collected during 75 min of 6.5 cm h⁻¹ rain. Runoff bioavailable P (BAP) and dissolved reactive P (DRP) increased linearly with increased P rate, STP, DPS_ox, and DPS_M3 but curvilinearly with DPS_STP Correlations between DRP or BAP and soil tests or saturation indices across soils were greatest (r ≥ 0.95) for FeP, OP, and WP and poorest for BP and TPS (r = 0.83–0.88). Excluding the calcareous soil (Calciaquoll) significantly improved correlations only for BP. Differences in relationships between runoff P and the soil tests were small or nonexistent among the noncalcareous soils. Routine soil P tests can estimate relationships between runoff P concentration and P application or soil P, although estimates would be improved by separate calibrations for calcareous and noncalcareous soils. Copyright © 2006. American Society of Agronomy, Crop Science Society of America, Soil Science Society . ASA, CSSA, SSSA