1. Institute for Rural Engineering, National Agriculture and Food Research Organisation, 2-1-6, Kannondai, Tsukuba-shi, Ibaraki 305-8609, Japan.
2. Corresponding author.
3. Kagoshima Prefectural Institute for Agricultural Development, 2200, Ono, Kinpo-cho, Minamisatsuma-shi, Kagoshima 899-3401, Japan.