Impact of Cow Dung Manure on the Solubility of Copper, Lead, and Zinc in Urban Garden Soils from Northern Nigeria

Abstract

Maintaining the quality of groundwater is a major consideration when developing management practices to effectively use cow dung manure (CDM) as a nutrient source and soil conditioner in agricultural production systems. This study examines the effect of CDM on the solubility of copper (Cu), lead (Pb), and zinc (Zn) in urban garden fields from Kaduna under long-term vegetable production. Soil samples were collected from Kakau, Kakuri, Trikaniya, and Romi in Kaduna metropolis in northern Nigeria. Soil–manure mixtures at the rate of 100 g CDM kg−1 soil were incubated for 2 weeks and analyzed for exchangeable [0.1 M calcium chloride (CaCl2)–extractable], mobile [1 M ammonium nitrate (NH4NO3)–extractable], and potentially labile [0.05 M ethylenediaminetetraacetic acid (EDTA)–extractable] copper (Cu), lead (Pb), and zinc (Zn). Addition of CDM increased exchangeable Cu in Kakuri and Romi and exchangeable Pb in Kakau and Kakuri, but decreased exchangeable Zn across the sites. The addition of CDM increased mobile Cu and Pb in all the sites. Although there was a decrease in mobile Zn in Kakau and Romi after the soil–manure incubation period, mobile Zn increased in Trikaniya and Kakuri. Furthermore, CDM decreased potentially labile Cu, Pb, and Zn in all the sites except for Romi, which increased labile Cu. To sustain the quality of soil and minimize groundwater pollution and food chain contamination, use of CDM in urban garden soils polluted with Cu, Pb, and Zn should be regulated or discouraged entirely to reduce the mobility of these metals.