Experimental Site: A field experiment was carried out during Aman season (20 July, 2013 to 28 November, 2013) in the field of the Department of Environmental Science at BAU farm. The location experiences a tropical monsoon-type climate, with a hot and rainy summer, and dry winter. Annual mean air temperature around 25.22 °C and the highest mean temperature is reached in the month of April. Annual rainfall is about 2249 mm where 70% of the annual rainfall is received during monsoon season (June to August). The relative humidity varies from 60-98% with some diurnal fluctuations in the various seasons with annual average of 56.8. The soil is dark gray non-calcareous floodplain) with a sandy loam and loam texture (UNDP and FAO, 1988).
Treatments: The experiment was laid out in a randomized complete block design (RCBD) with 6 treatments and 3 replications. The area of each plot was 10m2 (4m × 2.5m). The treatments were T1: Control plot (No fertilizer); T2: Inorganic fertilizers N, P, K (Standard doses); T3: Compost 10 t ha-1; T4: Compost 20 t ha-1; T5: Compost 30 t ha-1 and T6: Compost 50 t ha-1. At the time of final land preparation compost fertilizer was applied at the rate of 10, 20, 30 and 50 t ha-1 for T3, T4, T5 and T6 plots respectively. At that time Urea fertilizer (granular) was applied to T2 plots as basal dose @ 150 kg ha-1. Rest of Urea was applied at 2 equal splits at 30 and 60 DAT (Days After Transplanting). Triple super phosphate (TSP) and muriate of potash (MoP) were applied as basal dose (at the time of final land preparation) @110 and 60 kg ha-1. Sulphar and Zinc fertilizers were also applied as basal dose @45 kg ha-1 both. Forty five days old rice seedlings of cultivar BRRI dhan49 was transplanted in July 2013. The crops were harvested on 25 November, 2013 (110 DAT).
Plant Sampling: Data on growth and yield components were recorded from 5 randomly selected hills for each plot. Grain and straw yield were recorded on the whole plant basis. The grain and straw weight were expressed in t ha-1. The 1000 grain weight was taken from oven dried (72°C for 48 hours) grain samples of each unit plot. Harvest index was calculated by Fageria et al., (2011).
Gas Sample Collection and Analysis: Gas samples were collected using a modified closed-chamber method during the rice cultivation (Khan et al., 2015). The dimension of close chambers was 60 cm x 60 cm x 75 cm that was equipped with an electronic fan. Six chambers were installed for three times in each treatment of the experimental plot. Gas was sampled at 7-10 days interval and sampling time was 12.00- 2.00 pm. Gas samples were collected in 50 ml gas-tight syringes at 5, 10 and 30 minutes intervals after chamber placement over the rice planted plot separately. The gas samples were stored on 6.5cm pre-evacuated gas vials. The samples were analyzed to determine the concentration of CH4 gas by gas chromatograph equipped with a Flame Ionization Detector (FID) (Shimadzu-2014, Japan). The analysis column used a stainless steel column packed with HAYSEP Q 80/100.The temperatures of column, injector and detector were adjusted at 120ºC, 200ºC, and 220ºC respectively. The column flow was 25 ml/min.
Soil Analysis: After the harvest of rice crop soil samples from 0 – 15 cm depth were taken from individual plots. After completion of collecting soil samples, the unwanted materials like stones, granules, plant parts, leaves etc. were discarded from sample. The samples were dried at room temperature, crushed, mixed thoroughly and sieved with a 2 mm sieve. Soil pH and soil EC were analyzed by using pH meter electrode (McLean, 1982) and soil organic matter by The Walkley-Black Wet digestion method (Walkley and Black, 1934).
Statistical Analysis: Data were analyzed for CH4 emission and yield characteristics statistically by Analysis of Variance (ANOVA) to examine whether treatment effects were significant or not. Mean values were compared by Duncan's Multiple Range Test (DMRT). The software package, MSTAT-C was used for statistical analysis.