and 60 days after seeding (DAS) at the rate
of 75 mL and 100 mL, respectively. Both
growth enhancers were mixed with 20 L of
water for 1 ha of paddy field to boost the
growth.
During the first season (April-August,
2010), there was an extended dry period
during the vegetative and reproductive
phases. Therefore, water needed to be
pumped from the nearest drainage canal
(acidic water) to ensure that the rice seeds
were germinated. On the other hand, there
was no water limitation during the second
season (September 2010-January 2011) due
to intermittent heavy rainfall throughout the
season. The crop of rice was harvested in
August 2010 and January 2011 for the first
and second seasons, respectively.
Soil Sampling and Chemical Analysis
Soil sampling was carried out three times:
(i) before rice planting of the first season
(April 2010); (ii) after the first harvest
(August 2010); and (iii) after second
harvest (February 2011). Only topsoil (0-
15 cm) was sampled and three samples
were taken from each experimental plot
using a soil auger. After air-drying, the soil
samples were ground and passed through
a 10-mesh sieve (2 mm). The following
soil analyses were carried out: (i) Soil pH
was determined in water at soil to solution
ratio of 1:2.5; (ii) cation exchange capacity
(CEC) was determined by 1 M NH
4
OAc at
pH 7 (Chapman, 1965); (iii) exchangeable
Ca, Mg and K in the NH
4
OAc extract were
determined by Perkin Elmer Analyst 400
atomic absorption spectrometry (AAS); (iv)