Author
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Acock, Mary |
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Johnson, Emanuel |
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Submitted to: Journal of Plant Nutrition
Publication Type: Peer Reviewed Journal Publication Acceptance Date: 3/16/1998 Publication Date: N/A Citation: N/A Interpretive Summary: Worldwide yields of narcotic crops are estimated for the U.S. Congress annually. To improve our ability to forecast changes in yields of the coca crop, simulation models are needed that show how changes in environmental variables can change yields. Understanding plant response to nitrogen availability is fundamental to model development. This experiment examined how a range in nitrogen (N) availability affected N status of various parts of the coca plant and components of yield. Yields (i.e., leaf dry weight) increased with increased N availability, but leaf cocaine concentration was not affected. Increased N availability increased (a) the number of growing points on the plant, (b) the number of leaves per growing point, and (c) the size of old leaves. Leaf yields correlated with the N status of leaves, but N status alone was not a strong predictor of yield. Developing a simulation model that shows the effects of nitrogen availability along with other environmental variables will improve our ability to generate accurate figures for the U.S. Congress on illegal production of narcotic crops worldwide. Technical Abstract: Estimating yields (leaf dry weights) of Erythroxylum coca var. coca Lam. (coca) in regions where there is no direct access requires a method that can be used remotely. A simulation model that characterizes coca growth under varying weather conditions offers such a method. To develop this model, crop response to its environment must be quantified. The current experiment examined how a range in nitrogen (N) availability affected N status of various parts of the coca plant and components of yield. Minimal and maximal values for N concentration in leaves, stems, and roots were determined and N status calculated. Young leaves (a small yield component) had the highest N concentration, the greatest demand for N, and showed the greatest N stress. Old leaves had the next highest N concentration and a high demand for N, but showed the lowest N stress. N status in old leaves was most affected by N availability. Dry weights of each leaf type increased with increased N availability, but leaf cocaine concentration was not affected. Stems and taproots had the lowest N concentrations and these were not affected by N availability. Lateral roots, closer to the source of N, had N concentrations that reflected N availability, however lateral root dry weights were not affected by N supply. Increased N availability increased (a) the number of growing points on the plant, (b) the number of leaves per growing point, and (c) the size of old leaves. Increases in these components translate into increased yields. Leaf yields correlated with the N status of leaves (r = 0.58, p less than or equal to 0.001), but variability in leaf yields for a given N status was too high to have strong predictive power. |
