Effect of Temperature and Solar Radiation on Dry Matter Production of Spinach for Processing Use

Abstract

To achieve the stable supply of spinach for processing use, scheduled harvest based on growth prediction is effective. In this study, we investigated the effect of temperature and solar radiation on the dry matter production of spinach, and quantified the relationship. The leaf area index (LAI) was fitted with a logistic curve with integrated temperature as the explanatory variable. The fraction of radiation intercepted by the foliage was approximated by 1-exp(–0.69 × LAI) when LAI was below 3.26, and was constant at 0.89 in the higher LAI range. Average radiation-use efficiency was 0.98 g·MJ^–1, which was approximated by a logarithmic function with the mean temperature of the previous three days as the explanatory variable. The model constructed based on these relationships was validated using the growth data obtained in a different year. As a result, the logistic relationship between the integrated temperature and LAI was applicable for three data-sets obtained from cultivation tests with different planting dates. For a data-set in which early growth was retarded, minor adjustment of the integrated temperature improved the fit of the model. The correlation coefficient between estimated and observed dry matter production based on the modified model was 0.98.