The Levels of Nitrogen, Phosphorus, Potassium, Calcium and Magnesium in the Leaves of Cacao (Theobroma Cacao L.) as affected by Shade, Fertilizer, Irrigation, and Season

Abstract

The results are given of chemical analyses of leaves collected over a period of two years from cocoa trees in a field trial receiving fertilizer, shade, and irrigation treatments. The greatest variation in concentration of nutrients in the leaves was due to the time of year the leaves were collected. The lowest concentrations of nitrogen, phosphorus, and potassium were found in the leaves collected during the peak of the main season harvest. The highest levels of these elements were found in leaves collected near the end or a few weeks after the end of the main harvest. The levels of calcium in the leaves were just opposite, with the highest levels coinciding with harvest and the lowest levels occurring just after the harvest period. The levels of magnesium showed no marked variations between seasons. Shade increased the levels of nitrogen, phosphorus, and potassium, and decreased the levels of calcium in the leaves. Fertilizer increased the levels of nitrogen, phosphorus, calcium, and magnesium, and decreased the level of potassium in the leaves. The effect of irrigation was small, but it decreased the levels of nitrogen, potassium, calcium, and magnesium in the leaves. The levels of nitrogen, phosphorus, and potassium in the leaves over the 21 harvesting times were found to be positively correlated with each other, and all three were negatively correlated with the levels of calcium in the leaves over the same period. None of the levels of these four elements was significantly correlated with the levels of magnesium in the leaves over the period.