Influence of nitrogen forms and levels on the growth and nutrition of cacao

ABSTRACT

Ammonium and nitrate are the major forms of nitrogen (N) present in tropical soils. An experiment was conducted to assess the influence of nitrate and ammonium forms (NO₃⁻, NH₄⁺, and mix of NO₃⁻ + NH₄⁺), and levels (1.5–12.0 mM) of N on the growth and nutrition of cacao (Theobroma cacao L). Growth parameters were significantly influenced by N forms, and nitrogen supplied as NH₄⁺ proved better for the growth of cacao compared with NO₃⁻ form and mixtures of these two forms. Irrespective of the forms of N, levels of N had no significant effect on plant growth parameters. Nutrient efficiency ratios (NERs) (shoot dry matter produced per unit of nutrient uptake) for macronutrients were sulfur>phosphorus>calcium>magnesium>nitrogen>potassium (S>P>Ca>Mg>N>K) and for micronutrients NERs were in the order of copper>boron>zinc>iron>manganese (Cu>B>Zn>Fe>Mn).

KEYWORDS:

• NH₄⁺ and NO₃⁻ forms of N
• root and shoot growth
• relative growth rate
• macro and micronutrients influx
• nutrient efficiency ratio

Acknowledgments

The authors thank Dr. C. D. Foy for excellent peer review of this paper and Dr. Regina Cele R. Machado of Mars Center for Cocoa Science, Itajuipe, Bahia, Brazil for providing the cacao pods.