Experiments were conducted at AIT facilities in Bangkok
in a greenhouse with open sides and plastic roof (light
transmissivity 93%). The black clay soil, used for this
experiment, had 66.2% clay, with pH (1:1) of 5.0. Organic
carbon was 1.38%; total nitrogen 0.14%; available P
11 ppm; available K 212 ppm; and cation exchange
capacity 22.6 cmol kg-1. Sixty-five kilograms of soil were
placed in each plastic pot (60 cm high, with 50 cm top and
40 cm bottom diameters). The pots were flooded by adding
distilled water to a depth of 3–4 cm for a week before
transplanting, and they were dressed with 138 mg N kg-1
and 12.3 mg P kg-1 applied in NPK fertilizer: 16:16:0 as
basal application, and urea (46:0:0) was added at 15 and
45 days after transplanting (DAT). Single 15-day-old
seedlings of the variety Pathumthani (photoperiod nonsensitive;
maturity period = 120 days) grown in a dry
(SRI) nursery seedbed were transplanted when they had
two fully expanded leaves, within 2 h of uprooting from
the nursery seedbed, and at a depth of 1.5 cm.