This paper studied the relationship between tree age, nutrient dynamics and cocoa yield to determine which resources may limit cocoa yield. The study involved surveys of 14 cocoa agroforests in Central Sulawesi, including soil characterisation and analysis, and pod sampling for yield estimates, bean weight and carbon/nutrient analysis. Soil carbon nutrient levels did not change over the timeframes of 8 and 15 years and there was no relationship between soil carbon/nutrient levels and bean weight or carbon/nutrient levels. Phosphorus was the most limited nutrient in cocoa yield and the authors suggest phosphorus fertiliser applications and liming to increase phosphorus availability. The authors conclude that cocoa-gliricidia agroforests are only sustainable in the immediate future. The paper suggests investigating alternative species of shade trees to gliricidia, such as cashew nuts or macadamias that do are not shallow rooted like cocoa and are therefore not going to compete with cocoa for nutrients in the same soil strata. The authors comment on the benefits of using a chrono-sequence as a research tool but also highlight its limitations.
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Smiley G.L. and Kroschel J.
Agroforestry Systems 78(2), 97-114