Recent cadmium (Cd) regulation in chocolate threatens the sustainability of cacao production in Southwest America. Cadmium contamination in cacao beans has not been assessed at a country level. A nationwide survey was conducted in Ecuador to identify the spatial distribution of Cd in cacao beans, as well as soil and agronomic factors involved. Paired soil and plant samples (pods and leaves) were collected at 560 locations. Information on agronomic practices was obtained through a prepared questionnaire for farmers. Total soil Cd averaged 0.44 mg kg which is typical for young and non-polluted soils. Mean Cd concentration in peeled beans was 0.90 mg kg and 45% of samples exceeded the 0.60 mg kg threshold. Bean Cd hotspots were identified in some areas in seven provinces. Multivariate regression analysis showed that bean Cd concentrations increased with increasing total soil Cd and with decreasing soil pH, oxalate-extractable manganese (Mn) and organic carbon (OC) (R = 0.65), suggesting that Cd solubility in soil mainly affects Cd uptake. Bean Cd concentration decreased a factor of 1.4 as the age of the orchard increased from 4 to 40 years. Bean Cd concentration was inconsistently affected by genotype (CCN-51 vs. Nacional), pruning or application of fertilizers. It is concluded that the relatively larger bean Cd concentrations in Ecuador are related to the high Cd uptake capacity of the plants combined with their cultivation on young soils, instead of Cd depleted weathered soils. Mitigation strategies should consider the application of amendments to modify such soil properties to lower soil Cd availability. There is scope for genetic mitigation strategy to reduce bean Cd, but this needs to be properly investigated.
Biochars
have been shown as promising materials for cadmium remediation.
However, the different precursors and the pyrolysis process operating
conditions can yield very different surface functional groups, and
as a result, different cadmium sorption mechanisms can be observed
in biochars. Herein we present the results of cadmium sorption on
biochars produced from the pyrolysis of different agro-residues, namely,
coffee husk, quinoa straw, and oil palm kernel shell. The adsorption
isotherms were used to determine the influence of the biochar’s
physicochemical characteristics to their sorption behavior. The biochars
prepared from quinoa residues showed much higher cadmium uptakes than
the other biochars. The concentration of base cations was found to
be a critical factor for cadmium sorption. Although the quinoa biochars
presented large uptakes, it was found that base cations were supported
on the biochars and could be removed by leaching. Results from this
study suggest that concentration of base cations on biochars could
be used as predictors of the biochar capabilities for the removal
of cadmium in aqueous solution.
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Cocoa-based agroforestry (AF) systems are a conspicuous element of agricultural landscapes worldwide. Shade canopy analysis and design is a key component of crop husbandry, and requires a good understanding of the interactions, synergies and trade-offs between shade, yield and environmental services. In this chapter we provide a guide and some principles to analyse and design an optimal shade canopy that provides a diverse, resilient AF system. We first review the different cocoa system typologies described in the literature, placing special emphasis on cocoa–timber systems. We present a guide for the analysis of the shade canopy of shaded cocoa systems, and then investigate the optimal design for cocoa shade canopies, with emphasis on the analysis of trade-offs and synergies between carbon storage and cocoa yields. Finally, we consider critical issues in applying AF science/knowledge to cocoa cultivation programmes.
Elevated plant-available cadmium (Cd) in soils results in contamination to cacao (Theobroma cacao L) beans. Effectiveness of vermicompost and zeolite in reducing available Cd in three cacao-growing soils was studied under laboratory conditions. Sorption-desorption experiments were conducted in soils and amendments. Cadmium was added at 0 or 5 mg kg(-1) (spiked), then, amendments were incorporated at 0, 0.5, or 2 %. Amended soils were incubated at room temperature for 28 days. Plant-available Cd was determined using 0.01 M CaCl2 (WSE) and Mehlich 3 (M3) extraction procedures in subsamples taken from individual bags at six time intervals. Soils and amendments displayed different sorption characteristics and a better fit was attained with Freundlich model (R (2) > 0.82). Amendments were ineffective in reducing extractable Cd in non-spiked soils. In Cd-spiked soils, vermicompost at 2 % significantly reduced WSE-Cd (P < 0.01) from 3.36, 0.54, and 0.38 mg kg(-1) to values lower that instrument's detection in all the three soils and significantly diminished M3-extractable Cd (P < 0.05) from 4.62 to 4.11 mg kg(-1) in only one soil. Vermicompost at 0.5 % significantly decreased WSE-Cd (P < 0.01) from 3.04 and 0.31 to 1.69 and 0.20 mg kg(-1), respectively, in two soils with low sorption capacity for Cd. In contrast, zeolite failed to reduce WSE- or M3-extractable Cd in all studied soils. A negative correlation occurred between soil pH and WSE-Cd (r > -0.89, P < 0.01). The decrease in WSE-Cd appears to be associated with the increase in pH of the vermicompost-amended soils.
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