Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/6/1998
Publication Date: N/A
Interpretive Summary: Estimating the yield of illicitly grown Erythroxylum coca 'Coca' is difficult and dangerous. Methods that will allow us to rapidly and accurately assess the crop in the field are examined. One method uses light interception of leaves to estimate yield. The other method uses a subsample of the crop to estimate the whole. Each method has its strengths and weaknesses but both offer an objective means of estimating yields that can be used to improve crop production figures.
Technical Abstract: To determine the extent of world coca (Erythroxylum) production, methods for rapid estimation of yield (leaf mass) are required. The objective of this research was to compare two methods for rapidly acquiring data to estimate yield. The PCA method was based on measuring canopy light interception with the LI-COR Plant Canopy Analyzer (PCA), calculating leaf area index (L), and converting L to leaf dry weight using specific leaf area (SLA) values. The canopy subsample method was based on calculating leaf dry weight of a subsample from leaf and branch number, leaf size, and SLA, then multiplying by the ratio of the canopy volume to the subsample volume. PCA measurements underestimated leaf yields when values of L were greater than or equal to 1.0. PCA estimates could be corrected by adjusting for the observed difference between leaf yields and PCA estimates. The corrected PCA and canopy subsample methods had errors of similar magnitude, both slightly underestimating yield. Both methods performed well when tested against data from a subsequent harvest. The canopy subsample method uses simple equipment and can be applied in almost any environmental condition, but requires more time in the field than the PCA method. The corrected PCA method has slightly less random error than the canopy subsample method but requires expensive equipment, uniform light conditions in the field of view, and cannot be applied when raining.