Enhanced ammonium supply,soil pH and electrical conductivity effects on spring wheat growth

Spring wheat (Triticum aestivum L.) dry matter (DM), N content and tillering are increased by increasing the proportion of N available to the plant as NH₄ (enhanced ammonium supply‐EAS) at soil pH ≥ 7.0. Using different N sources to provide different levels of EAS effects soil pH and electrical conductivity (EC) as well as soil NH₄. Both pH and EC may affect plant growth and response to EAS.

Two greenhouse experiments were conducted to determine the effects of EAS, pH, and EC on the DM, N content, and tillering of spring wheat. The collinearity between pH and NH₄ was eliminated over a pH range of 5.8 to 7.2 by adjusting lime rates to compensate for the effect of each N source on pH. Even though EC was somewhat correlated with soil NH₄ in both experiments, there were a sufficient number of comparisons to separate the effects of EC and NH₄ on plant growth. Differences in plant growth resulted from differences in soil NH₄ levels. Soil pH and EC did not affect plant growth. Plant responses to soil NH₄ levels were quadratic. Maximum plant growth occurred at approximately 100–200 mg/kg KCl‐extractable NH₄.