Tropentag, September 16 - 18, 2026, Göttingen "Towards multi-functional agro-ecosystems promoting climate-resilient futures"

Irrigation, biochar, and fertiliser management shape cadmium accumulation in cacao beans: Long-term agroforestry field study

¹The Alliance of Bioversity International & CIAT, Peru
²Universidade de Lisboa, Centro de Química Estrutural, Portugal
³Deutsche Landwirtschafts-Gesellschaft DLG e.V, Germany
⁴Universidad Científica del Sur, Facultad de Ciencias Ambientales, Peru

Abstract

Cacao (Theobroma cacao) is a globally traded commodity and a key export for small-scale farmers in Latin America. However, many countries struggle to meet European cadmium (Cd) thresholds for chocolate and its derivatives. This makes field-scale mitigation strategies essential. Biochar shows promise for ameliorating Cd and improving soil fertility. Nevertheless, knowledge remains limited on how biochar and fertilisers interact to balance Cd mitigation under field features and their heterogeneity. To address this, a four-year randomised trial was conducted in a cacao agroforestry system in Piura, northern Peru. The trial tested commercial biochar (produced at 650–859 °C from pruning and poultry manure, and composted with trace FeSO₄), fertiliser, and their combinations. The site featured clay loam soil (1.2% organic matter, pH 5.7, 1.7 ± 0.6 mg Cd kg^-1) and initial bean Cd of 7.7 ± 2.1 mg kg^-1. Multivariate modelling revealed key findings as follows: (1) proximity to irrigation channels consistently increased bean Cd levels, likely due to Cd influx from upper-valley mining and irrigation-driven erosion; (2) presence of Cedrela odorata trees and higher local soil pH both moderately reduced bean Cd levels; (3) Biochar application led to a reduction in bean Cd by up to 26%, primarily by liming and enhanced adsorption, but levels still exceeded the critical threshold for trade (≥1.2 mg kg^-1); (4) Fertiliser application increased bean Cd, likely due to soil acidification, competitive sorption, and increased root uptake, and diminished the positive effects of biochar. Overall, field-irrigation conditions and plot heterogeneity exerted a stronger influence on bean Cd content than treatments alone, indicating the necessity for integrated water and soil management. Improved fertilisation regimes and exploration of biochar optimisation, including coated and functionalized variants, are necessary to achieve Cd compliance in cacao beans for international trade.

Keywords: Circular economy, crop modelling, low-input systems, Theobroma cacao, watershed

Contact Address: Manuel G. Velasquez Ramirez , The Alliance of Bioversity International & CIAT, Avenida La molina 1895, Lima, Peru, e-mail: fc65228alunos.ciencias.ulisboa.pt