Abstract:
Essential secondary macronutrients ( Ca, Mg, S) and trace elements (Fe, Mn, B, Cl, Zn, Cu, Mo) present in relatively low concentrations in NPK fertilizers could be necessary for maintaining the life processes in plants. On the other hand some beneficial elements (such as Cr, Co, Ni) and trace elements (such as Cd, As, Pb) present in relatively low concentrations and above the maximum allowable limit in NPK fertilizers can be toxic or non-essential to plants threatening plant production, the environment and the animal-human health. The main objective of this study was to analyze secondary exchangeable macronutrients and selected trace elements in fertilizers that are commonly used in Lasta Woreda. The samples were wet digested with concentrated HCl and the concentrations of the metals in fertilizers were determined using Inductively Coupled Plasma Optical Emission Spectrometry (ICP-OES). The concentrations of metals in Urea were found to be Ca (152.2±0.6), Mg (0.9±0.04), Fe (140±6), Cu (37.4±0.35), Cr (10.1±0.11), Ni (172.9±2.29) and Cd (4.3±0.05) in mg/kg. The concentrations in NPSB (Urea Diammonium Phosphate Ammonium Sulphate with Borax) fertilizer were found as Ca (12±0.24), Mg (20.9±0.16), Fe (9.2±2.76), Cu (59.70±0.82), Cr (7.3±0.13), Co (3.2±0.69), Ni (8.3±0.8) and Cd ( 66.1±0.50) in mg/kg. Urea contained more essential and beneficial metals than NPSB except where Cobalt was not detected in it. The fertilizers Urea and NPSB that are used in Lasta Woreda contains both secondary macronutrients and trace elements as impurities. The concentrations of most trace metals were below the regulatory limits of these metals in fertilizers by most countries except Cd in NPSB which is slightly higher than allowed limits of China, Canada and USA-Texas. Long term application of NPSB fertilizers in current composition may lead to accumulation of Cd in environment. Thus, the quality of fertilizers used in the country has to be regulated periodically for essential and non-essential secondary and trace metal levels for sustainable use.
Keywords: Lasta Woreda, Fertilizers, Macro and Micronutrients, ICP-OPES