Growth, yields and mineral nutrition of cupuaçu (Theobroma grandiflorum) in two multi-strata agroforestry systems on a ferralitic amazonian upland soil at four fertilization levels

Abstract

Cupuaçu (Theobroma grandiflorum) is an economically important Amazonian tree crop and a common component of agroforestry systems on the infertile soils of the Amazon region. To provide farmers with recommendations on nutrient management for this species, information on the relationships between fertilizer input, nutrient availability in the soil, foliar nutrient levels, growth and yield of the trees under the local pedoclimatic conditions are required. Cupuaçu was grown for seven years in two multi-strata agroforestry systems with four fertilization levels on a xanthic Ferralsol in central Amazonia. Yields were measured during the last four years, and the biomass of the trees was estimated from an allometric regression in the last year. Growth and yield data were compared with soil and leaf analyses from both systems. In one system, leaf samples of three age classes and four collection dates during a year were analysed to determine a sampling protocol with maximum sensitivity for differences in mineral nutrition for the species. The cupuaçu yields were significantly influenced by fertilization level and cropping system. Soil and leaf analyses suggested that the yield response was mainly to P fertilizer, whereas N fertilizer did not seem to affect growth and yields of the plants. The soil data were easier to relate to the cupuaçu yields than the leaf data, apparently because the trees responded to greater nutrient inputs with increased vegetative growth rather than with increased nutrient concentrations in the leaves. However, foliar analyses gave useful additional information on limiting nutrients and suggested that the trees in an unlimed treatment developed a latent Mg deficiency which may affect crop yields in the future. The pronounced difference in growth and yield of cupuaçu between the two multi-strata systems could not be explained with foliar analyses, and with soil analysis only by taking into account the fertility of the soil under previous intercrops planted between the trees. Sampling recommendations for foliar analysis of cupuaçu are given. For soil analysis in agroforestry systems with spatially heterogeneous nutrient availability in the soil, sampling of a sufficiently large area around the target trees is essential.