Grain N and P relationships in maize

Relationships between P and N concentrations in the shoot biomass and the uppermost collared leaf have been established in maize (Zea mays. L.) with the idea of using this N:P stoichiometry for developing an in-season plant-based diagnostic of P deficiency. Much less is known of the grain N and P relationship and its potential for a posteriori diagnostic of maize nutrition. The objectives of this study with maize were to determine: (1) the effect of N fertilization on grain N and P concentrations, (2) the relationship between grain P and N concentrations at sites known to have adequate soil P for growth, and (3) critical grain N and P concentrations and ratios of N to P that could be used for a posteriori diagnostic of N and P deficiencies. A field experiment was conducted at 10 site-years (2004–2009) in Québec, Canada, with three to six N fertilization rates (0–250 kg N ha−1). Maize grain yield, and N and P concentrations were determined at harvest. Increasing N fertilization increased grain N concentration at most site-years but decreased grain P concentration and increased the N to P ratio at four of the 10 site-years. Grain P concentration tended to decrease slightly with increasing grain N concentration (P = 1.32 + 0.38 N − 0.02 N2, R2 = 0.32; P < 0.001). This weak relationship and the small change in P concentration with increasing N concentration limit its potential use for a posteriori diagnostic of P deficiency in maize. Risks of having a low relative grain yield tended to be greater when the N to P ratio in the grains was less than 4.0. We conclude that, contrary to vegetative tissues, the N and P stoichiometry in maize grains is non existent, hence limiting the potential of the grain N and P relationship for diagnostic purposes.

► Increasing N fertilization increased grain N concentration but tended to decrease grain P concentration.
► Grain P concentration decreased slightly with increasing grain N concentration.
► This small change in P concentration limits its potential use for a posteriori diagnostic of P deficiency.
► Contrary to vegetative tissues, N and P stoichiometry in maize grains in non existent.