Contribution of Pruning Residues to Carbon and Nutrient Cycling in Cacao Monocultures and Agroforestry

Summary

Background and aims
Cacao in agroforestry systems can benefit from improved nutrient cycling, since shade trees could transfer nutrients through litterfall and pruning residues. Additionally, shade trees could affect decomposition processes of these residues. Studies on nutrient release from pruning residues and on the effect of shade trees on decomposition processes are scarce. We aimed to determine how cropping systems (agroforestry, monocultures) affect the decomposition of pruning residues and quantify nutrient release by these residues.
Methods
Litterbags with two mesh sizes (0.1 and 2 mm), containing leaf mixtures, were placed under five cropping systems (conventional and organic monocultures, conventional and organic agroforestry, successional agroforestry) in a long-term trial in Alto Beni, Bolivia. Carbon, phosphorus, nitrogen, potassium, cellulose, and lignin were measured in fresh leaves and litterbags at 4, 8, and 12 months after laying.
Results
Nitrogen was higher under conventional agroforestry than under the other systems at 4 months after laying. Phosphorus was higher under agroforestry than under monocultures at 8 months after laying. Litterbags with 2 mm mesh size contained lower amounts of carbon and nutrients at 4 months after laying than litterbags with 0.1 mm mesh size. Release of nutrients from pruning residues was estimated.
Conclusions
The effect of shade trees on decomposition processes was limited to changes in nitrogen and phosphorus contents in litterbags. Larger mesh litterbags likely favoured microbial colonization and nutrient transfer through leaching. The nutrient input from pruning residues could meet the potassium and nitrogen demands of cacao but is insufficient for phosphorus.