Potential of Organic and Inorganic Amendments for Stabilizing Nickel in Acidic Soil, and Improving the Nutritional Quality of Spinach

Contamination of soils by nickel (Ni) has become a serious environmental problem throughout the world, and this substance wields dangerous effects on the ecosystem and food chain. A pot experiment was conducted to examine the effect of rice straw (RS), rice straw biochar (BI) and calcite (CC) at 1% and 2% application rates in a Ni contaminated soil. The objective was to potentially stabilize Ni and reduce its bioavailability to spinach (Spinacia Oleracea L.). Spinach plants were grown in a Ni contaminated Ultisol (commonly known as a red clay soil). Physiological results indicated that a BI 2% application rate significantly increased the photosynthetic rate by 4-18.6 µmol m2 S− 1 and transpiration rate by 1.7–8.9 mmol m2 S− 1. Similarly, growth parameters for root and shoots dry biomass increased 1.7- and 6.3-fold, respectively, while essential nutrients were enhanced in the spinach plant compared to those in the untreated soil (CK). Moreover, adding amendments significantly decreased CaCl2 extractable Ni by 62.5% 94.1%, and 87.2%, while the toxicity characteristics leaching procedure (TCLP) fell by 26.7%, 47.8%, and 41.7% when using RS, BI and CC, respectively, at 2% compared to CK. The Ni concentrations in the spinach roots declined by 51.6%, 73.3% and 68.9%, and in the shoots reduced by 54.1%, 76.7% and 70.8% for RS, BI and CC, at a 2% application rate, respectively. Bio-concentration factor (BCF) and translocation factor (TF) dropped significantly by as much as 72.7% and 20%, for BI 2% application rate. Results of the present study clearly indicated that biochar potential soil amendments for Ni stabilization, thereby reducing its bioavailability in the Ni contaminated soil. This process enhanced the safety of food to be consumed and mitigated security risks.