Abstract
Constancy of three kinds of heat unit accumulation required for silking of corn cultivated in Northern Kyushu was compared using the data of 14-24 experiments with different sowing dates. The cultivars used were early variety G4321A, medium variety G4810A, late variety P3160 and Ko-3 bred in Japan. The kinds of heat unit accumulation used were: simple heat unit accumulation (SHUA), which is the accumulation of daily mean temperatures above 0°C, effective heat unit accumulation-I (EHUA-I), which is the accumulation of daily mean temperatures above 10°C, and effective heat unit accumulation-II (EHUA-II), which is the accumulation of daily mean temperatures above value a(°C) in the formula, Y=aX+b, where X and Y are the number of days and SHUA from sowing to silking, rspectively. The coefficient of variation (C.V.) was as large as 7.9-10.9% and that of EHUA-I was 5.1-9.3%. On the other hand, C.V. of EHUA-II was only 2.5, 3.2 and 5.2% in G4321A, G4810A and P3160, respectively, showing a high constncy. In Ko-3, C.V. of EHUA-II was 8.5%, probably because this cultivar is sensitive to photoperiod.
