Organic carbon and nutrient dynamics under crop-livestock farming system in Haramaya and Kersa Districts,Eastern Ethiopia

Crop-livestock farming system is a traditional and main agricultural practice in the eastern part of Ethiopia, where crop grains are produced for food security and residues are for animal feed and domestic fuel consumption. As a result, farmers practice crop residues removal management throughout the cropping seasons. However, there is no adequate information on the impacts of crop residues removal management on soil properties and crop yields under such farming system. These studies analyze the status of soil properties under crop-livestock farming system, phosphorus adsorption capacity of the soils, organic carbon and nutrient distribution, and transport under crop residues removal management practices, and effects of crop residue incorporation on soil properties and crop grain yield at two farms, Adele in Haramaya and Bala Langey in Kersa districts in Eastern Ethiopia. Soil samples were collected from the crop fields and homesteads at both farms and analyzed following standard methods for soil physical and chemical analyses as well as for P adsorption capacities. Haricot bean was intercropped with maize for two cropping seasons for residue incorporation at both sites. Results reveal that soils of both farms have same textural class, sand clay loam but are different in other properties. The pH of the soils at both farms was in the range of 6.50 to 7.50 which is a suitable range for most crops grown at both sites. Soil organic carbon (<1.5%), nitrogen (<0.2%), extractable P (< 10 mgkg-1) and sulfur (<5 mgkg-1) were low and are the soil productivity limiting factors associated with soil fertility at both farms. Soils of Adele farm had higher P adsorption capacity from KH2PO4 and DAP than soils of Bala Langey farm. Thus, soils of the two farms demand different P fertility management strategies. Distribution of organic carbon and nutrients in the farming system at both farms was highly affected by poor management of manure, household wastes and crop residues. About 2.95 and 2.15% OC was accumulated near homes of the households, respectively, at Adele and at Bala Langey ii farms. The quantity was less than 2% in the crop fields at both farms. About 100 and 41 mg Pkg-1 was accumulated near home at Adele and Bala Langey farms, respectively. But extractable P was low (< 15 mgkg-1) in the crop fields at both farms. Other nutrients follow similar trends. Through incorporation of haricot bean residue under maize haricot bean intercropping system, soil bulk density values decreased from 1.38 to 1.21 gcm-3 at Adele site and from 1.34 to 1.20 gcm-3 at Bala Langey site. Soil organic carbon increased from 1.21 to 1.99% at Adele site and from 1.19 to 2.14% at Bala Langey site. CEC increased from 56.50 to 66.58 cmol(+)kg-1 at Adele site and from 56.77 to 59.13 cmol(+)kg-1 at Bala Langey site. Haricot bean residue incorporation significantly (P