Data for: Effect of biochar on micronutrient availability and uptake into leafy greens in two urban tropical soils with contrasting soil pH

Soils were collected from small urban vegetable farms in Kumasi and Tamale. Each soil sample was air-dried and sieved to < 2 mm prior to analysis Biochars were produced from corn cobs (Zea mays), rice husks (Oryza sativa) and teak sawdust (Tectona grandis) and pyrolyzed using an ELSA barrel or a Japanese Retort Stove The same feedstocks were used to make biochar using a muffle furnace at 300°C, 500°C and 700°C. All biochars were then ground to a fine powder using a TEMA mill (Laboratory Disc Mill T100ACH) prior to analysis Water extracts of soil-biochar mixtures were determined by weighing 3.8 g of soil into a polypropylene centrifuge tube along with 0.2 g of biochar (apart from the unamended control treatment, which received only the 3.8 g of soil) and shaking on an end-over-end shaker at 30 rpm for 16 hours at 20°C and then pH of the biochar/soil slurry was analyzed. The tubes were immediately centrifuged at 3600 rpm for 10 minutes and the supernatant filtered through 0.45 µm syringe filters. Dissolved Organic Carbon (DOC) was analyzed in the filtered supernatant. A 10 mL sub-sample of the filtered supernatant was acidified with 5% HNO3 and analyzed for multiple elements using ICP-MS. Seeds of Amaranthus, Corchorus, and Lettuce (var Eden F1) were germinated in a coco coir medium for one week and transplanted into experimental 3 liter pots (n = 9). 1kg of air-dried soil from either Kumasi or Tamale was added to each plot, amended with 50g of biochar at a rate equivalent to 5% (w/w). Plants were watered daily and weekly assessments were made of plant growth, including the number of leaves on each plant, the height, and the girth of the stems at 5 cm from the surface of the soil. After 4 weeks the plants were harvested, leaves were removed from the stem and the fresh weight of both the leaves and the stem were taken. Leaves were dried, at 60°C overnight in paper envelopes, re-weighed and then milled prior to analysis with ICP-OES after microwave digestion. Three pots were randomly selected and the soils remaining rhizosphere in each pot were homogenized and one ~50 g sub-sample per pot air dried prior to analysis of EDTA extractable elements using ICP-OES, electrical conductivity (EC), and pH. A full description of the methods is provided in Rodríguez-Vila, A., Atuah, L., Abubakari, A.H., Worlanyo Atorqui, D., Alhassan, A.K., Coole, S., Hammond, J., Robinson, S. and Sizmur, T., 2022. Effect of biochar on micronutrient availability and uptake into leafy gree