The Impact of Woodland Conversion to Cropland on Selected Soil Properties in Upper Didessa Valley,South West Ethiopia.

A field experiment was conducted at Wondo Genet Agricultural Research Center from March, 2009 to December, 2009 to examine the effects of plant population desity and harvesting age on leaf, essential oil and artemisinin yield of Artemisia annua. The experiment consisted of factorial combinations of four harvesting ages (four, five, six and seven months after transplanting) and five evels of plant population desity (6,944,10,000, 15,625,27,777 and 49,383 plants ha-1). The design used was split-plot with three replications. Harvesting age was assigned to main plot and plant population desnisty on sub plot.The effects of harvesting age and plant population desnity were assessed by analyzing datat on growth, yield and yield components of A. annua. Results revealed that interaction effects of harvesting age and plant population desnity was significant on stem number plant. stem number ha-1, plant height, leaf area index, shoot dry weight plant. dry leaf yield ha-1, harvest index and artemisinin yield. Dry leaf yield plant and artemisinin content were affected significantly be harvesting age and plant population density. Branch number plant-1, essential oil content and essential oil yield were affected significantly by plant population density. In this study, maximum dry leaf yield of 3.15 t/ha was attained at plant population desnity of 27,777 plants ha-1 and harvesting at 5 MAT. Essential oil yield of 19.2kg/ha was also recorded at plant population density of 27,777 plants ha-1 regardless of harvesting ages.The maximum artemisinin yield of 10.9kg ha-1 was obtained at plant population densityof 27,777 and harvesting at 7 MAT. There was no significant artemisinin yield increment above this density.The above finding clearly showed that,optimum dry leaf, essential oil and artemisinin yield cna be achieved by planting A. annua at plant population density of 27,777 plants ha-1 and harvesting at 5 MAT for dry leaf yield and 4 to 7 MAT for essential oil yield. Since atremisinin yield has increased up to 7 MAT, the last harvesting age used in this study, it is difficult to know the optimum linit. Therefore, further investigation is needed to determine the optimum harvesting age by harvesting at later stage. In addition, these results are from only one season at one site and hence it should be repeated to reach at concrete recommendations.Furthermore, planting time, fertilizer requirement, irrigation requirement, drying condtion and processing techniques should be addressed to obtain optimum yield of the crop.