The relationship between climate condition in autumn and soluble solids content of daikon 'Fuyushokunin' in Hiruzen region, Maniwa city

1. For establishing a suitable sowing period to harvest daikon with high sugar content that matches the shipping standard weight, we investigated the relationship between pre-harvest weather conditions and soluble solid content (SSC) measured in Brix%. Furthermore, we examined differences of SSC among thickening root parts and assessed the effects of applied nitrogen fertilizer on SSC. 2. Surveys conducted both in late October and mid-November revealed that SSC tended to be higher at the upper part of thickening roots. SSC increased from the end of October through mid-December. The degree of the increase was 0.2 to 0.5 Brix% for the whole thickening root, whereas we found 1.1 to 1.2 Brix% at the upper part. 3. The leaf weight tended to decrease as the nitrogen fertilization amount became smaller for 1.0 to 3.0 kg/a, which is the cultivation standard of the producing area. Nevertheless, the effects on root weight and SSC were unclear. 4. A regression analysis was conducted using 44 data for four years in a field at an altitude of about 460 m and for one year in a field at an altitude of about 600 m. Results show that SSC in the upper part of the thickening root tended to increase as the average of the daily minimum air temperatures for 40, 30, 20, 15, 12, and 10 days before harvest became lower (R**2 = 0.6). Significant negative correlation was found with accumulated rainfall for 20 days before harvest (R**2 = 0.3). 5. Based on the two variables, a multiple regression equation was prepared. 6. The following calculations could be used to predict SSC easily in a field during cultivation: either the average of the daily minimum air temperature for 30 days before harvest in a year when the total integrated precipitation after October 1 is greater than about 356 mm, or that for 12 days in a year when precipitation after October 1 is less than or equal to about 356 mm.