FERTILIZER FORMULATION EFFECT ON PH OF FALLOW VERSUS PLANTED CONTAINER SUBSTRATE

Abstract

From previous work testing the impact of 30 fertilizers on substrate pH, five fertilizer formulations that elicited the widest range of substrate pH biotic impacts during Salvia farinacea ‘Evolution White’ cultivation were chosen for a follow up study to determine the abiotic impact of these fertilizers on fallow substrate. A 3 sphagnum peat moss : 1 perlite substrate was formulated and adjusted to pH 5.6. Three sets of pots (14 cm diameter) were filled with substrate. Salvia plugs were installed in the first set for cultivation while the second set was left fallow followed by fertilization of both sets with 400 mL of fertilizer solution with each irrigation (each at 7 mmol nitrogen concentration and pH 4.2 ± 0.1) to bring them to approximately container capacity. The third set of pots (control) was left fallow and irrigated with 400 mL deionized water instead of fertilizer solution. When cultivated substrates dried to approximately 50% of container capacity, 200 mL of fertilizer solution was applied to sets one and two and 200 mL deionized water to set three for a total of 11 applications. Substrates were harvested after 3 and 6 weeks. The pH of control substrate was 5.69 for both harvests. For the first and second harvest, cultivated substrate pH ranged from 6.08 to 5.03 and 6.22 to 4.85, respectively, while pH values of fallow substrate that received fertilizer solutions ranged from 5.66 to 5.19 and 5.44 to 4.97, respectively. Contrary to the expected abiotic effect of these acidic fertilizer solutions, pH in the fertilized fallow pots increased or decreased in a similar but diminished fashion to the changes that occurred to the pH in the cultivated pots. These results suggested a biotic effect in the fallow substrates due possibly to microflora and nitrification and indicate the need to take into account a biotic effect of microbes when assessing the abiotic effect of fertilizer solutions on substrate pH.