Influence of biochar-based organic amendments on yield and concentration of heavy metals in tomato fruits, grown in chromite mine tailing debris-contaminated soil, under field conditions

Palwasha Achakzai ¹ Shamim Gul ^2* Dr. Kanval Shaukat ¹ Hidayatullah Kakar ³ Zahoor Ahmed ³ Sadaf Aslam Ghori ⁴ Tasawar Ali Chandio ⁵

• ¹ University of Balochistan, Quetta, Balochistan, Pakistan
• ² McGill University, Montreal, Canada
• ³ Agricultural research Institute, Quetta, Balochistan, Pakistan
• ⁴ Sardar Bahadur Khan Women's University, Quetta, Balochistan, Pakistan
• ⁵ Geological Survey of Pakistan, Quetta, Quetta, Pakistan

In this study, top soil layer (0-15 cm) was contaminated with chromite at 1 t ha-1 rate for two years. Air-dried manures from sheep and goat (S/G), poultry (PM), and cow and buffalo farms (FYM) were combined at 1:1:1 ratio, followed by their further mixing separately with wood-derived and manure-derived biochars (50% biochar and 50% manure mixture). Biochars were also combined with synthetic NPK fertilizer. All these fertilizers were added to contaminated soils for two years at 5, 10, and 20 t ha-1 rates (or 0.5, 1 and 2 kg m-2 amendment rate in 1 x 1 m plot). In another experiment, wood-derived biochar was co-composted with the mixture of above-mentioned manures as well as co-composted separately with S/G, PM and FYM manures. These co-composted biochar fertilizers were amended to chromite-contaminated soil at10 and 20 t ha-1 rates. Two tomato varieties were taken into account for this study. Results showed that the amendment of fertilizers for two years and one year amendment of co-composed biochar fertilizers did not increase the yield of large tomato fruit variety. For both cropping years, very few treatments improved yield of small tomato fruit variety. Tomato crops were not negatively impacted by the chromite contamination.Fertilizers did not lower the concentration of lead in tomato fruits, except for large sized wood-derived biochar and manure-derived biochar, amended at 5 t ha-1 rate. These treatments reduced the concentration of lead in the fruits of small tomato fruit variety of second year crop (P<0.05). Cadmium was not detected ; whereas, chromium was detected in only two samples of tomato fruits. This experiment suggests that crops may not take heavy metals in high concentration for few years following the deposition of metal(loids) from mining activities into the transported soils of agricultural lands of the region Muslim Bagh, Balochistan, Pakistan.