Combined nitrate and phosphorus application promotes rhizosphere alkalization and nitrogen uptake by wheat but not canola in acid subsoils

Abstract

Purpose: Excess anion uptake in the form of nitrate has been shown to reduce soil acidification. The question is to what extent the deep placement of calcium nitrate can increase this root-induced alkalization in reducing subsurface soil acidity. Methods: Wheat and canola were grown for 35 days in reconstructed soil columns comprising of topsoil (pHCaCl2 5.4) in 0–10 cm and subsurface soil (pHCaCl2 4.8) in 10–50 cm. Two forms of 15N-enriched fertilizers (urea versus calcium nitrate at 237 mg N per column) with or without P fertilizer (NaH2PO4 at 99 mg P per column) were placed at 0–10, 10–20, or 20–30 cm depth. Root proliferation, rhizosphere pH, and shoot 15N recovery were quantified. Resul..