**2.1 Plant cultivation and experimental plots**

The field experiment was conducted at the Field Science Centre of Okayama University (34°41' N, 133°55' E, Japan) in 2001 and 2002. The texture of the soil was sandy clay and preceding crop was pumpkin. Indeterminate soybean (*Glycine max* (L.) Merr.) cv. 'Enrei' (maturity group III) was used. Two seeds were sown on 13 and 14 June in 2001 and 2002, respectively, with an 80cm (wide) and 30cm (narrow) row-spacing, and sparse (11.1 plants m-2, 11.25 and 30cm plant spacing in wide and narrow row-spacing, respectively) and dense (22.2 plants m-2, 5.6cm and 15cm in wide and narrow row-spacing, respectively) planting density. Each plots size was 57.6 m2 (3.2×18.0m)with no replication. A basal fertilizar was applied at the rate of 2.1g N, 4.4g P and 10.0g K. Herbicide was applied to the soil surface to avoid weed emergence. The plants were thinned to a plant per hill when primary leaves were fully expanded. In wide row plots, soil molding was conducted by a rotary cultivator. The crop was irrigated with a water-spraying vinyl hose placed on every other row. Recommended pesticides were applied for the control of insects and diseases.
