Statistical model for describing macronutrient impacts on container substrate pH over time

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Abstract

Although many factors that influence substrate pH have been quantified, the effect from fertilizers continues to be elusive. A multifactorial experiment was conducted to test macronutrient effects using a rarely used statistical method known as the central composite design. Five nutrient factors, including nitrogen (N) carrier ratio (NH4+ vs. NO3-) and concentrations of phosphorus (P) (as H2PO4-), potassium (K), combined calcium (Ca) and magnesium (Mg), and sulfur (S), were varied at five levels each encompassing the proportionate range of these nutrients in commercial greenhouse fertilizers. Although a typical factorial experiment would have resulted in 55 = 3125 treatments, the central composite design reduced the number to 30 fertilizer treatments. An experiment was conducted twice in which 'Evolution White' mealy-cup sage (Salvia farinacea Benth.) was grown in 14-cm-diameter pots (1.29 L) in a 3 peat:1 perlite (v/v) substrate amended with non-residual powdered calcium carbonate to raise the substrate pH to ≈5.6 to 5.8. Harvests occurred after 3 and 6 weeks of growth. A statistical model described substrate pH over time with significant effects including four main effects of N carrier ratio, P, K, and combined Ca and Mg; three squared terms of N carrier ratio, P, and K; and seven interaction effects. The resulting model was used to calculate substrate pH levels between 25 and 45 days after planting, and it showed that N carrier had the greatest impact on substrate pH.

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Barnes, J., Nelson, P., Whipker, B. E., Dickey, D. A., Hesterberg, D., & Shi, W. (2014). Statistical model for describing macronutrient impacts on container substrate pH over time. HortScience, 49(2), 207–214. https://doi.org/10.21273/hortsci.49.2.207

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