Abstract
In the Matto area of Ishikawa Prefecture it is recommended that manure be applied to the popular rice variety Koshihikari, 18 days before its heading date. To help farmers to determine the timing of this fertilizer application, we examined a way of estimating the heading date for crops seeded directly into flooded rice paddies. The heading date was taken as the date that the accumulated effective temperature, as calculated from the maximum and minimum temperatures each day after seeding, exceeds a certain reference value. The expression for calculating the effective daily temperature is as shown below:
Effective temperature=
(daily maximum temperature+daily minimum temperature)/2-10[°C]
Examinations were conducted at the Ishikawa Agricultural College Experimental Farm from 1998 to 2000. The average accumulated effective temperature between seeding and heading from 1998-2000 was 1263°C, which provides an indicator for estimating the heading date of Koshihikari. The standard deviation of the accumulated effective temperature over the three years was 14.9°C. The heading date of Koshihikari was estimated using a target temperature accumulation of 1263°C for the years 2001 to 2003. The actual heading date in 2001 and 2003 was one day later than estimated, and was five days later in 2002. The cause of the estimation error in 2002 was that the temperature after the last estimating day was markedly different from the monthly weather forecast. It was considered that a change of the target day for ear manuring was necessary in this situation.
