Screening of Ethiopian Traditional Medicinal Herbs for their Nitrification Inhibiting Ability

Abstract

Nitrification is the main cause of reduced N-use efficiency and yield of crops. Blending nitrogenous fertilizer with commercial or herb-based inhibitors is one of the means of increasing N-use efficiency. The objective of this study was to screen Ethiopian traditional medicinal herbs along with Neem (none traditional Ethiopian medicinal plant) and commercial inhibitors for their nitrification inhibiting ability. Soil samples were collected from Awassa Agricultural Research Center, Ethiopia. One hundred gram of processed soil was transferred to 250 ml capacity cups to which alcohol extracts of 11 herbs at 1% rate of dry soil were added separately. N-seve ([2-chloro-6 (trichloromethyl) pyridine]) and Dicyandiamide (DCD) were added at a rate of 2 and 100 μg/g of soil respectively. The cups were also amended with 50 mg of ammonium sulphate and the moisture was maintained at 60% water holding capacity (WHC) and incubated for various period at 25°C. At the end of each period, samples were analyzed for pH, NH4-N and NO₃-N. The result revealed that 72% of the tested herbs and commercial inhibitors conserved significantly high amount of NH₄-N, an indication of inhibition of nitrification, at the end of 2nd week. But from among Ethiopian medicinal herbs, only Artemis afra, Echinops spp and Eugenia caryophyllata inhibited nitrification at the end of 3^rd week. Averaged over two incubation periods, these herbs inhibited nitrification by 33, 37 and 64% respectively. Eugenia caryophyllata performed as effective as neem but none of the herbs out performed commercial inhibitors. Both medicinal herbs and commercial inhibitors prevented the soil from the acidification of the soil. There was a decline in inhibition percentage of all inhibitors with time but it was more drastic for herbs than commercial inhibitors. It is concluded that 3 Ethiopian medicinal herbs were identified as nitrification inhibitors. Thus, their extracts could be blended with ammonium fertilizers for increasing N-use efficiency of crops.