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Eleven crops were cultivated: maize, sunflower, soybean, groundnuts, sesame, kenaf, barley, wheat, rice, potato, and sweet potato. The crop growth rate (CGR) and specific dark-respiration rate (Rs) were measured, and growth efficiency GE =CGR/(CGR+R) (R, respiratory loss) was calculated. In each crop, whole-plant Rs reached a maximum in the earlier stages of growth, declined rapidly until the early reproductive growth, and remained almost constant during the ripening period. The Rs of leaves was higher than that of stems during the reproductive growth period, except for maize and potato. The Rs of storage organs was highest in the earlier stages, followed by a rapid decline to similar or lower values than those of leaves and stems during the ripening period. The GE in whole plant was higher than 60% in wheat, maize, barley, sunflower, rice, kenaf, sesame, but lower in soybean, sweet potato and groundnuts, and lowest in potato, which was affected by the higher respiratory loss. The GE in whole plant during the reproductive growth period was significantly lower, which we attributed to increased maintenance costs due to the increase of non-assimilative organs, and decrease in the dry weight of vegetative organs. A positive correlation was observed between the carbohydrate content of storage organs and GE, indicating that a crop with higher carbohydrate content in storage organs tended to have a higher GE. Crops with higher protein and crude fat content in storage organs tended to have lower GE. The GE over the growing season was low for kenaf, a fiber crop which contains high molecular weight compounds such as lignin and cellulose, and lower for sesame, groundnuts, and soybean, which contain high oil and protein and have high respiration costs for the synthesis of storage materials, suggesting that these higher respiration costs are related to lower dry matter production and hence lower yields.
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