Prevalence of heavy metals along rainfall gradient in sorghum-based cropping system in the SudanoSahelian Zone of Nigeria

One major thing Nigerian farmers give more emphasis on is the maintenance of soil fertility. This is done indiscriminately using any material the farmers perceive could maintain soil fertility. Many of such materials like refuse dumps, industrial wastes, household wastes, and farmyard manure are applied to maintain soil fertility oblivious of their chemical contents. From Kofa, southern Kano, to Zangon Daura at the Nigeria–Niger border, twelve sorghum-based communities were selected based on 50 mm rainfall gradient. In each community, ten farms of which sorghum was the main crop grown were selected and soil samples collected. One hundred and twenty composite soil samples were collected from the twelve communities. The samples were analyzed for pH and heavy metals using standard laboratory procedures. The heavy metal distribution along the rainfall gradient appears to vary according to pH and rainfall. The regions with higher rainfall amounts (900 and 850 mm) had the prevalence of Cd, Zn, and Ni. The regions with rainfall of 800 and 750 had a prevalence of Mn, while Fe and Pb were observed in regions with rainfall between 450 and 600 mm. Regions with rainfall of 650 mm had a prevalence of Cu. The soil pH and heavy metals were found to be within the normal range for agricultural soils based on World Health Organization (WHO) and the Food and Agriculture Organization of the United Nations (FAO) standards. The study concludes that the farmers’ efforts along this gradient are quite safe environmentally and health-wise. There is a need to encourage these farmers through the provision of subsidized inputs. Key words: Rainfall, heavy metals, sorghum, soil fertility.