Prediction of Radish Growth as Affected by Nitrogen Fertilization for Spring Production

The average annual and winter ambient air temperatures in Korea have risen by 0.7 and 1.4 °C, respectively, during the last 30 years. Radish (Raphanus sativus), one of the most important cool-season crops, may well be used as a model to study the influence of climate change on plant growth, because it is more adversely affected by elevated temperatures than warm season crops. This study examined the influence of transplanting time, nitrogen fertilizer level, and climate parameters, including air temperature and growing degree days (GDD), on the performance of a radish cultivar (Mansahyungtong) to estimate crop growth during the spring growing season. The radish seeds were sown from April 24 to May 22, 2012, at internals of 14 days and cultivated with 3 levels of nitrogen fertilization. The data from plants sown on April 24 and May 8, 2012, were used for the prediction of plant growth as affected by planting date and nitrogen fertilization for spring production. In our study, plant fresh weight was higher when the radish seeds were sown on April 24 than on May 8 and May 22. The growth model was described as a logarithmic function using GDD according to the nitrogen fertilization levels: for 0.5N, root dry matter = 84.66/{1+exp [–(GDD-790.7)/122.3]} (r² = 0.92), for 1.0 N, root dry matter = 100.6/{1+exp [–(x-824.8)/112.8]} (r² = 0.92), and for 2.0 N, root dry matter = 117.7/{1+exp [–(GDD-877.7)/148.5]} (r² = 0.94). Although the model slightly tended to overestimate dry mass per plant, the estimated and observed root dry matter and top dry matter data showed a reasonable good fit with 1.12 (R² = 0.979) and 1.05 (R² = 0.991), respectively. Results of this study suggest that the GDD values can be used as a good indicator in predicting the root growth of radish.