Ammonium-nitrate ratio and cation/anion uptake affect the acidity or basicity of floriculture species

R. Dickson, P.R. Fisher
Floriculture crops affect substrate-pH and consequently the solubility of micronutrients during commercial production. Studies with agronomic species have shown that roots affect rhizosphere-pH through an imbalance in the uptake of cation and anion nutrients. However, the relationship between cation-anion uptake and effect on solution acidity has not been evaluated with floriculture species. Data from a container study were analyzed and a hydroponics experiment was run to evaluate whether cation:anion uptake was related to solution acidity and basicity for three floriculture crops [geranium (Pelargonium × hortorum, Bailey. L.H.), petunia (Petunia × hybrid, Vilm.-Andr.), and impatiens (Impatiens wallerana, Hook. F.)]. In the container study, >96% of the applied nitrogen was supplied as NO3--N which resulted in all species having greater anion uptake. Petunia increased substrate-pH after four weeks, whereas geranium and impatiens did not change pH. When the same species were grown hydroponically in nutrient solutions with solution NH4+:NO3- ratios from 0:100 to 20:80 there was an approximately 1:1 relationship between net anion minus cation uptake and net solution acidity or basicity. The milliequivalent (mEq) solution acidity or basicity equaled 0.972±0.195*(net mEq of anions - cations taken up) + 0.140±0.478; adjusted-R2 = 0.739 over all species, which indicated a strong correlation between solution-pH change and net cation or anion uptake. Geranium had the highest cation/anion uptake ratio (1.06) and produced greater acidity than petunia, which had the lowest cation/anion uptake ratio (0.94). Cation/anion uptake ratio increased as applied NH4+:NO3- ratio increased. Adjusting fertilizer NH4+:NO3- ratio therefore strongly influenced the acidity or basicity effect of plants, and could be manipulated as a pH management tool in floriculture production.
Dickson, R. and Fisher, P.R. 2017. Ammonium-nitrate ratio and cation/anion uptake affect the acidity or basicity of floriculture species. Acta Hort. (ISHS) 1168:135-142
geranium, impatiens, Pelargonium, petunia, pH management

Acta Horticulturae