Browsing by Author "Coleman, K."
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Item Evaluation of two soil carbon models using two Kenyan long term experimental datasets(Elsevier, 2007) Kamoni, P. T.; Gicheru, P. T.; Wokabi, S. M.; Easter, M.; Milne, E.; Coleman, K.; Falloon, P.; Paustian, K.; Killian, K.; Kihanda, F. M.; Agriculture, Ecosystems & EnvironmentRothC and Century are two of the most widely used soil organic matter (SOM) models. However there are few examples of specific parameterization of these models for environmental conditions in East Africa. The aim of this study was therefore, to evaluate the ability of RothC and the Century to estimate changes in soil organic carbon (SOC) resulting from varying land use/management practices for the climate and soil conditions found in Kenya. The study used climate, soils and crop data from a long term experiment (1976-2001) carried out at The Kabete site at The Kenya National Agricultural Research Laboratories (NARL, located in a semi-humid region) and data from a 13 year experiment carried out in Machang'a (Embu District, located in a semi-arid region). The NARL experiment included various fertiliser (0,60 and 120 kg of Nand P205 ha -I), farmyard manure (FYM-5 and lOt ha -I) and plant residue treatments, in a variety of combinations. The Machang'a experiment involved a fertiliser (51 kg N ha- I ) and a FYM (0, 5 and 10 t ha- I ) treatment with both monocropping and intercropping. At Kabete both models showed a fair to good fit to measured data, although Century simulations for treatments with high levels of FYM were better than those without. At the Machang'a site with monocrops, both models showed a fair to good fit to measured data for all treatments. However, the fit of both models (especially RothC) to measured data for intercropping treatments at Machang'a was much poorer. Further model development for intercrop systems is recommended. Both models can be useful tools in soil C predictions, provided time series of measured soil C and crop production data are available for validating model performance against local or regional agricultural crops.Item Predicted Soil Organic Carbon Stocks and Changes in Kenya between 1990 and 2030(Ministry of Agriculture, 2007) Kamoni, P. T.; Gicheru, P. T.; Wokabi, S. M.; Easter, M.; Milne, E.; Coleman, K.; Falloon, P.; Paustian, K.; National Agricultural Research Laboratories, P.O. Box 14733, Nairobi, Kenya; The Natural Resource Ecology Laboratory, Colorado State University, Fort Collins, CO 80523-1499, USA; The Department of Soil Science, The University of Reading, P.O. Box 233, Reading RG6 6DW, UK; The Agriculture and Environment Division, Rothamsted Research, Harpenden, Herts ALS 2JQ. UK; The Met. Office, Hadley Centre for Climate Prediction and Research, Fitzroy Road, Exeter EXI 3PB, UKUnder the United Nations Framework Convention on Climate Change (UNFCCC), Non-Annex 1 countries such as Kenya are obliged to report green house gas (GHG) emissions from all sources where possible, including those from soils as a result of changes in land use or land management. At present, the convention encourages countries to estimate emissions using the most advanced methods possible, given the country circumstances and resources. Estimates of soil organic carbon (SOC) stocks and changes were made for Kenya using the Global Environment Facility Soil Organic Carbon (GEFSOC) Modelling System. The tool conducts analysis using three methods: (1) the Century general ecosystem model; (2) the RothC soil C decomposition model; and (3) the Intergovernmental Panel on Climate Change (IPCC) method for assessing soil C at regional scales. The required datasets included: land use history, monthly mean precipitation, monthly mean minimum and maximum temperatures for all the agro-climatic zones of Kenya and historical vegetation cover. Soil C stocks of 1.4–2.0 Pg (0–20 cm), compared well with a Soil and Terrain (SOTER) based approach that estimated ∼1.8–2.0 Pg (0–30 cm). In 1990 48% of the country had SOC stocks of <18 t C ha−1 and 20% of the country had SOC stocks of 18–30 t C ha−1, whereas in 2000 56% of the country had SOC stocks of <18 t C ha−1 and 31% of the country had SOC stocks of 18–30 t C ha−1. Conversion of natural vegetation to annual crops led to the greatest soil C losses. Simulations suggest that soil C losses remain substantial throughout the modelling period of 1990–2030. All three methods involved in the GEFSOC System estimated that there would be a net loss of soil C between 2000 and 2030 in Kenya. The decline was more marked with RothC than with Century or the IPCC method. In non-hydric soils the SOC change rates were more pronounced in high sandy soils compared to high clay soils in most land use systems.
