Abstract
As the first step to develop a model to explain and predict the dynamic relationship between weather and sweet potato crop growth and yield, we investigated the relationship between solar radiation absorbed by the canopy and the dry matter production in a cultivar “Koganesengan” grown for 5 years from 2004 to 2008. In 2005 and 2008, the correlation of leaf area index (LAI) with albedo, transmissivity and absorptivity were examined by the continuous measurements of the transmitting and reflected radiation. LAI and the dry weight were also examined by periodic harvesting. There was a proportional relation between total dry weight and the solar radiation absorbed by the canopy with a proportional coefficient of 5.51 g kWh-1. LAI was obtained as the product of total dry weight, leaf weight ratio and specific leaf area. Leaf weight ratio decreased exponentially with an increase in effective accumulated temperature above 10°C (∑T10). Tuberous root weight is given by multiplying total dry weight with harvest index. Although an allometric relation was found between total dry weight and harvest index in all experiments, the allometric coefficients determining the quantitative relationship between them varied mainly with the soil temperature at a 5 cm depth. On the basis of these results, an algorithm to predict the changes in LAI, total dry weight and tuberous root weight was developed using plant weight at planting time, mean soil temperature during the 5-week period after planting, daily air temperature and daily amount of insolation. The predicted values agreed with the observed values of total dry weight and tuberous root weight in spite of the assumption that specific leaf area was constant (0.03 m2 g-1).
