Measurement of CO2 Emission from Bio-Char-Amended Rice Paddy Field in the Coastal Savannah Zone of Ghana

Abstract

Agricultural practices affect the production and emission of Carbon dioxide (CO 2 ) from paddy soils. Evidence now exists on increased CO 2 concentration in the atmosphere as a result of decomposition of organic matter which impacts on climate change and global warming. The release of CO 2 from soil (soil CO 2 efflux or soil respiration) is the largest source of carbon to the atmosphere. In Ghana, the major challenge is lack of data on greenhouse gas (GHG) emission to form the basis of scientific debate. Furthermore, the efficacy of interventions such as bio-char application to reduce GHG emission from crop fields has not been investigated. This research presents a nine (9) months field and screen house experimental study aimed at measuring CO 2 emission from vertisols in the coastal savannah zone of Ghana and to assess the effect of bio- char in combination with irrigation treatments on the emission of CO 2 of the paddy system. The treatments for the field experiment were established following a split-plot design with soil amendment as main plot treatment and levels of N fertilization as the subplot treatment. The main plots were control (C), bio-char rice husk (BRH) and raw rice husk (RH). The subplots treatments were 0, 45, 90 and 120 kg N/ha applied as urea. The subplots were replicated three times and completely randomized in each main plot. The screen house study was set out in a Completely Randomized Design (CRD) with three types of soil amendment (BRH, RH and C), two fertilizer levels (0 and 90 kg N/ha) and two irrigation treatments (0 cm water head and 5 cm water head). These treatments were replicated three times. Soil CO 2 efflux was measured in-situ using closed chamber method during the whole study period. Generally, low CO 2 emissions were observed for BRH amended plots followed by C with relatively high emissions from RH amended plots. Soil CO 2 efflux increased with increasing level of N fertilizer. Higher emissions were recorded in the afternoon particularly, in mid- morning to afternoon (10-2 pm). Average weekly CO 2 efflux was higher in Season I than Season II over the nine-month study period. Comparing the soil amendment types, the highest mean CO 2 emission of 369 mg m -2 /4hrs was recorded from RH treatment whereas, CO 2 emission of 362 and 294 mg m -2 /4hrs was recorded from C and BRH amendment respectively during Season I. The lowest average CO 2 efflux of 205 mg m -2 /4hrs was recorded on the bio-char amended plots followed by RH and C plots with CO 2 efflux of 293 and 349 mg m -2 /4hrs respectively. The lowest average CO 2 emission of 199 mg m -2 /4hrs was also recorded on BRH amended plots. In the screen house study, lower CO 2 effluxes were recorded for flooded treatments than those kept at 0 cm water head. The regression of soil temperature on soil CO 2 efflux showed a positive correlation with CO 2 evolution increasing as temperature increases, and temperature contributing to 61% of the CO 2 efflux, as shown by the regression equation.