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Nutrient Management & Soil & Plant Analysis

Phosphorus Loss in Runoff from Long-term Continuous Wheat Fertility Trials

^a Dep. of Plant and Soil Sciences
^b Dep. of Statistics, Oklahoma State Univ., Stillwater, OK 74078
^c Apex Environmental Inc., Lenexa, KS 66215
^d Dep. of Agronomy and Environmental Management, Louisiana State Univ., Baton Rouge, LA 70803
^e Dep. of Crop and Soil Environmental Sciences, Virginia Polytechnic Institute and State Univ., Blacksburg, VA 24061
^f Yangzhou Univ., Jiangsu, China

^* Corresponding author (jschrod{at}okstate.edu)

Some wheat (Triticum aestivum L.) farmers in the southern Great Plains routinely apply P fertilizer without soil testing. This practice may lead to P buildup in soils, hence, increased P runoff potential, making soil P management of concern in continuous wheat production. At present, there is also debate over the nature of P loss trends, particularly whether soil P release to runoff can be described generally, across a broad range of soils, or is soil-specific. Paired 1 m by 2 m runoff plots were established on three existing long-term continuous winter wheat fertility experiments. Two experiments have received annual fertilizer P application at different rates since 1970 (0–44 kg P ha^–1), and the third received a one-time P application at much higher rates in 1977 (0–587 kg P ha^–1). Rainfall-runoff experiments were conducted following the National P Research Project protocol. Simulated rain (75 mm h^–1) produced 30 min of runoff from plots with different soil test P levels. Soil Mehlich-3 P (M3P) ranged from 11.5 to 130 mg kg^–1 and water-soluble P (WSP) ranged from 0.70 to 15.7 mg kg^–1. Runoff total P and dissolved reactive P (DRP) concentrations ranged from 0.47 to 1.5 and 0.03 to 0.70 mg L^–1, respectively. Dissolved reactive P in runoff was significantly related to M3P, WSP, and ammonium oxalate P saturation index (PSI_ox) for combined soils as well as for individual soil series. Significant differences (p < 0.05) among the slopes of the regressions for the DRP-M3P, DRP-WSP, and DRP-PSI_ox relationships indicate that the relationships are soil specific. This study highlights the need for soil specific management to protect water quality.

Abbreviations: Al_ox, ammonium oxalate extractable Al • DRP, dissolved reactive P • Fe_ox, ammonium oxalate extractable Fe • ICP–AES, inductively coupled plasma–atomic emission spectroscopy • M3P, Mehlich-3 P • NPRP, National Phosphorus Research Project • P_ox, ammonium oxalate extractable P • PP, particulate P • PSI_ox, ammonium oxalate P saturation index • S_max, phosphorus adsorption maximum • STP, soil test P • TSS, total suspended solids • TP, total P • USEPA, United State Environmental Protection Agency • WSP, water soluble P