Phosphorus‐induced Zinc Deficiency in Wheat on Residual Phosphorus Plots¹

One‐time heavy application of P on certain soils can provide sufficient available P to sustain crop production over a period of several years, but may cause Zn nutritional problem for crops. A field study was conducted to determine the effect of applied Zn on wheat ( Triticum aestivum L.) grown on residual P plots and identify the mechanism of P ✕ Zn interaction. This study was conducted in 1984 in a continuous wheat system on a clayey, mixed, frigid Typic Hyploboroll soil that had received 0, 80, and 160 kg P ha −1 in 1979. Three experiments were carried out using a split plot randomized complete block design with three levels of P as main plots and rates of soilapplied Zn‐sulfate (0, 5, 10, and 20 kg Zn ha −1 ) or Zn‐chelate (0, 0.5, 1.0, and 2.0 kg Zn ha −1 ) or foliar‐applied Zn‐chelate (0 and 0.35 kg Zn ha −1 ) as subplots. A one‐time application of 80 or 160 kg P ha −1 increased wheat yield significantly. In the presence of P, application of Zn resulted in significant increase in grain yield and Zn uptake into grain. Applied P increased soil P levels and tissue P concentration, but resulted in a significant decrease of tissue Zn levels. DTPA (diethylenetriaminepentaacetic acid)–extractable soil Zn levels in the non–Zn‐amended treatment were independent of P application rate. Plant roots in high P treatments contained significantly lower levels of vesicular‐arbuscular mycorrhizal (VAM) infection than the control. Further, a close relationship was observed between Zn levels in the aboveground plant parts and VAM infection.