Comparative analysis of the influence of watering regime and soil properties on greenhouse gas emission in Mwea irrigation scheme, Kirinyaga county, Kenya.

Abstract

The nexus of climate change and enhancing food sufficiency requires a better comprehension of how to balance food demand with climate change mitigation to promote sustainability. This study quantifies the influence of watering regimes, crop establishment methods, and soil properties on greenhouse gas emissions in rice fields, specifically within the Mwea irrigation scheme in Kenya. The study aimed to analyze the influence of two different watering regimes namely alternate wetting and drying (AWD), and continuous flooding (CF) on greenhouse gas emissions in transplanted rice (TPR) and direct-seeded (DSR) rice. Additionally, it investigated the influence of soil properties on greenhouse gas emissions. To accomplish this, an on-station experiment with four treatments: CF + TPR, CF + DSR, AWD + TPR, AWD + DSR, and four replications were performed for one season. The experiment was laid out in a randomized complete block design with a split-plot arrangement where the watering regimes were the main plot and the crop establishment methods were the subplots. 60ml propylene syringes were used to collect the gas samples from the closed static gas chamber method, after which the samples were then transferred into 40-ml glass vials. The gas samples were transported to the Mazingira Centre laboratory and analyzed for (CH4, N2O, and CO2) using a gas chromatograph (GC; model SRI 8610C). Soil samples were collected using a soil corer (8cm height) at a depth of 0-16cm and 17-32cm and analyzed for pH, CN, PSA, water content, ammonium, nitrate, and phosphorus using the globally recognized protocols at the Mazingira Centre, within the International Livestock Research Institute (ILRI) in Nairobi, Kenya. The results on the influence of watering regimes, crop establishment methods, and their interactions on greenhouse gas emissions were statistically subjected to a two-way analysis of variance (ANOVA) test followed by a Turkeys multiple comparison test where the influence was found to be significant. Additionally, to determine the influence of soil properties on greenhouse gas emissions the results were statistically analyzed using a Pearson’s correlation test. Both watering regimes and crop establishment methods and their interactions significantly influenced the emission of CH4 (P < 0.01). Crop establishments significantly influence the emission of CO2 (P< 0.05) with higher emissions in DSR subplots irrespective of the watering regime. However, there was no significant influence of the watering regimes, crop establishments, or their interactions on the emission of N2O. Watering regimes greatly influenced the global warming potential. Regardless of the crop establishment method, AWD decreased the potential for global warming compared to continuous flooding. However, the interaction between AWD and DSR had a higher global warming reduction potential compared to other treatments. Sand content showed strong negative and positive correlations with CH4 (P < 0.05) and CO2 (P < 0.01) respectively. The nitrate content and N2O exhibited a strong positive correlation (P < 0.01). Regarding water use, AWD saved 64% of the water used compared to CF. In conclusion, this study found AWD to be a preferable way to continuous flooding to mitigate the potential for global warming while direct-seeding rice under alternate wetting and drying was proven to be a more effective practice to reduce global warming potential (GWP).