Evaluation Ofselected Management Practices Contributing To Primary Soil Greenhouse Gas Fluxes In Smallholder Sugarcane Farming In Lower Nyando, Westernkenya

ABSTRACT Human activities (including agriculture) contribute to enhance release of primary greenhouse gases (GHGs) (CH4, CO2, N2O) into the atmosphere leading to global warming. Sugarcane is an important economic crop in Kenya being third highest contributor to gross domestic product (GDP) after tea and coffee. About 90% of Kenya‘s production is contributed by smallholders. To improve/maximize sugarcane yields, farmers convert natural vegetation to sugarcane farms; apply nitrogen fertilizers; retain residues in-situ to return nutrients, and organic carbon to the soil or burn residues to ease management. High GHGs emissions have been observed in temperate countries due to such agronomic activities. However, contribution of these activities to GHGs fluxes in smallholder sugarcane sector in tropical countries, especially along the equator is not documented. This study evaluated contribution of smallholder sugarcane farming management practices to GHGs fluxes in Lower Nyando, western Kenya and compared fluxes with those from high agronomic input large-scale sugarcane farming in temperate countries. Cross-sectional survey in Lower Nyando Block revealed that smallholder sugarcane growers‘ management practices included; period of land conversion to sugarcane farming, nitrogen fertilization and trash management. From survey, six sugarcane farms:-three with less than and three with more than 10 years conversion period to sugarcane production were selected to conduct trials on soil GHG flux measurement. Each farm was subjected to burned and unburned treatments with three rates of nitrogen fertilizer 0, 50, 100 kg N / ha/ year in factorial three design in randomized complete block design arrangement, replicated three times in three separate farms. Soil gas samples were collected weekly for 37 weeks and analyzed using gas chromatography. There was CH4 absorption in all treatments. Conversion period from natural vegetation/other cropping systems to sugarcane cultivation did not influence GHGs fluxes. Nitrogen fertilization and burning residues increased (p≤0.05) N2O and CO2 emissions between weeks 12 to 14 and 3 to 10 respectively. Cumulatively, treatments did not cause significant differences in GHGs fluxes. Levels of GHGs fluxes were much lower than those from large-scale sugarcane production systems in temperate countries. The low levels indicate use of Tier 1 factors to estimate GHG emissions in the tropics may produce inaccurate data. The results demonstrated that smallholder sugarcane management systems in Lower Nyando Block do not contribute significantly to GHGs emissions and hence climate change. Farmers can continue with these management practices to limit GHGs emissions to mitigate climate change.