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 greater-than-or-equal-to 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.