Preliminary study of chemical fertilizer and cattle manure-based bio-slurry application on soil properties and heavy metal concentration in maize (Zea mays L.) grain.

The objective of this study was to evaluate the effect of bio-slurry (BS) and chemical fertilizer (CF) application on the physico-chemical properties of the soil and food safety of maize (Zea mays L.) grain. A field experiment was conducted at Hawassa University Research Farm, in Sidama Region, Ethiopia, under rain-fed conditions. The experiment consisted of three treatments, arranged in a randomized complete block design with three replications. The treatments were 100 % BS (5 ton BS ha^-1), 100 % CF (90 kg N ha^-1+ 30 kg P ha^-1 + 13 kg S ha^-1) and control. Soil samples were taken for the physico-chemical analysis. Maize grain samples were also collected at harvest for the analysis of heavy metal concentration. The application of BS and CF slightly improved the soil physico-chemical properties. The mean concentration of heavy metals in pre-experiment soil was below the permissible limit for arable land except Cd. Though the application of BS reduced the mean concentration of most of the heavy metals studied (Mn, Pb, As, Cd, Cr, Ni and Co), it increased the concentration of essential metals (Cu, Fe and Zn) in soil. Likewise, the application of CF increased the concentration of Cu and Fe. The application of BS and CF increased the concentration of Ni and Co, respectively, in maize grain that exceeded the FAO/WHO 2001 standards. Attributing to heavy metal concentration, this result signifies a potential health concern of applying BS and CF in maize cultivation for human consumption in the study sites. Therefore, pretreatment of BS and CF for Ni and Co is important for avoiding heavy metal contamination of maize grain for human consumption.