Determination of optimal fertilizer concentration range for tomatoes grown in peat-based medium

Abstract

For optimum plant growth in containers, adequate plant nutrition is essential. Objectives of this research were to determine the optimum fertilization of tomatoes (Lycopersicon esculentum Mill.) in a peat-based medium and to assess plant nutrition by plant and media analysis. Tomato seedlings (‘Heinz 1437’) were transplanted (one plant per pot) into 2-liter pots filled with a peat-based medium. The medium was fertilized with a progressive array of soluble fertilizers to supply N from 0 to 200 mg L^{− 1} of solution with accompanying proportional increases of other macronutrients with each increase in nitrogen (N) (P from 0 to 44; K from 0 to 160; Ca from 0 to 200, and Mg from 0 to 48 mg L^{− 1}). The plants were irrigated starting with 100 mL of fertilizer solution per day and increasing to 200 mL per day as plant growth progressed. The tomatoes were harvested at three stages of growth (5-leaf stage, flower initiation, and fruit formation) for analysis of growth and composition. Samples of medium for nutrient analysis were taken at each growth stage. Plant biomass increased linearly as fertilizer level increased or as time progressed. Generally, concentration of extractable nutrients in the medium increased linearly with increases in nutrients in the solutions. However, as time progressed, N concentrations in medium rose, but phosphorus (P), potassium (K), calcium (Ca), and magnesium (Mg) in the medium fell. Concentrations of N, P, or K in leaves increased as nutrition increased, but Mg or Ca in leaves had no significant changes with increased nutrient supply. With time the N, P, Ca, and Mg concentration in tissues fell, but K rose. Assessment of plant nutrition was best at flower initiation, with assessments at the other stages of development being judged as untimely or excessively variable. For maximum growth, critical concentrations of nutrients in the medium (mg kg^{− 1}) at flower initiation were judged to be 30 NO₃-N, 30 P, 300 K, 2600 Ca, and 800 Mg and in leaves (g kg^{− 1}) to be 35 N, 10 P, 70 K, 35 Ca, and 20 Mg. Fertilization to reach these critical concentrations was reached in the regime with 100 mg N L^{− 1} or higher levels of nutrition.

Acknowledgments

This publication, no. 3300 in the Massachusetts Experiment Station Journal Series, is based on work supported by the Cooperative State Research, Extension, Education Service, U.S. Department of Agriculture, and the Massachusetts Agricultural Experiment Station, under Project No. 756.