Fertilizer ammonium : nitrate ratios determine phosphorus uptake by young maize plants

Pedersen, I.F. and Sørensen, P. and Rasmussen, J. and Withers, P.J.A. and Rubæk, G.H. (2019) Fertilizer ammonium : nitrate ratios determine phosphorus uptake by young maize plants. Journal of Plant Nutrition and Soil Science. ISSN 1436-8730

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Abstract

We investigated the interacting effects of inorganic nitrogen and the main inorganic phosphorus form in dairy manure (dicalcium phosphate, CaHPO 4 ) on growth, nutrient uptake, and rhizosphere pH of young maize plants. In a pot experiment, three levels of CaHPO 4 (0, 167, and 500 mg P pot −1 ) were combined with nitrogen (637 mg N pot −1 ) applied at five NH 4 -N : NO 3 -N ratios (0 : 100, 25 : 75, 50 : 50, 75 : 25, and 100 : 0) and a nitrification inhibitor in a concentrated layer of a typical acid sandy soil from Denmark. 15 N-labeled NH 4 -N was applied to differentiate the role of nitrification and to partition nitrogen uptake derived from NH 4 -N. Among treatments including nitrogen, shoot biomass, rooting and phosphorus uptake were significantly higher at the five-leaf stage when CaHPO 4 was applied with NH 4 -N : NO 3 -N ratios of 50 : 50 and 75 : 25. In these treatments, rhizosphere pH dropped significantly in direct proportion with NH 4 -N uptake. The fertilizers in the concentrated layer had a root-inhibiting effect in treatments without phosphorus supply and in treatments with pure NO 3 -N or NH 4 -N supply. Increased nitrogen uptake as NH 4 -N instead of NO 3 -N reduced rhizosphere pH and enhanced acquisition of applied CaHPO 4 by young maize plants, which may have positive implications for the enhanced utilization of manure phosphorus.