Modeling impact of nitrogen carrier and concentration on root substrate pH

An experiment was conducted to investigate the impact of nitrogen (N) carrier and concentration on substrate pH. The study utilized four different N concentrations ranging from 3.5 to 14 mM and five fractions of ammonium (NH4 +) ranging from 0% to 80% of total N, representing common formulations in commercial fertilizers. These fertilizers were applied to small pots with a specific substrate mixture, and the substrate pH was adjusted to around 6.0 by adding calcium carbonate.

The experiment involved two harvests, one at 20 days and another at 42 days. The statistical model used in the analysis revealed significant effects, including main effects of N carrier and N concentration, squared terms for these factors, an interaction effect, and a time-dependent effect related to N carrier.

Notably, the fraction of NH4 + in the fertilizer formulations had a significant impact, accounting for 45.0% of the variation in substrate pH. In contrast, N concentration contributed to only 1.5% of the total variability in the results, which had an overall R-squared value of 76.7%. The observed substrate acidification was attributed to the physiological effect of the fertilizer and the process of nitrification.