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 greens in two urban tropical soils with contrasting soil pH. Frontiers in Sustainable Food Systems. doi: 10.3389/fsufs.2022.821397本研究土壤样品采自库马西（Kumasi）和塔马利（Tamale）两处小型城市蔬菜农场。所有土壤样品在分析前均经风干处理，并筛分至粒径<2 mm。 生物炭以玉米芯（Zea mays）、稻壳（Oryza sativa）以及柚木锯屑（Tectona grandis）为原料制备，分别采用ELSA炭化桶与日本式蒸馏炉进行热解。此外，以相同原料在马弗炉中分别于300℃、500℃和700℃下制备生物炭。所有生物炭在分析前均经TEMA研磨机（实验室圆盘磨T100ACH）研磨为细粉。 土壤-生物炭混合物的水提液制备及测定流程如下：称取3.8 g土壤与0.2 g生物炭置于聚丙烯离心管中（未添加生物炭的对照处理仅加入3.8 g土壤），于20℃下以30 rpm转速的滚轴式摇床振荡16小时，随后测定该生物炭-土壤悬液的pH值。离心管立即以3600 rpm转速离心10分钟，上清液经0.45 μm针式过滤器过滤。取过滤后上清液测定溶解性有机碳（Dissolved Organic Carbon, DOC）。另取10 mL过滤上清液，用5%硝酸（HNO3）酸化后，采用电感耦合等离子体质谱（ICP-MS）测定多种元素含量。 以苋菜（Amaranthus）、黄麻（Corchorus）以及生菜（品种Eden F1）的种子为试验材料，在椰糠基质中萌发1周后，移栽至3 L规格的试验盆钵中，每个处理设置9次重复（n=9）。每盆加入1 kg风干的库马西或塔马利土壤，并添加50 g生物炭，施用量相当于5%（质量分数，w/w）。每日对植株进行灌溉，每周测定植株生长指标，包括单株叶片数、株高以及距土壤表面5 cm处的茎粗。种植4周后收获植株，剥离叶片并称取叶片与茎秆的鲜重。叶片置于纸质信封中于60℃下过夜烘干，再次称重后研磨，经微波消解后采用电感耦合等离子体发射光谱（ICP-OES）进行元素分析。 随机选取3个盆钵，收集各盆中残留的根际土壤并混匀，每个盆取约50 g子样品进行风干处理，随后采用ICP-OES测定乙二胺四乙酸（EDTA）提取态元素含量，并测定土壤的电导率（EC）与pH值。 本研究方法的完整细节参见如下文献：Rodríguez-Vila, A., Atuah, L., Abubakari, A.H., Worlanyo Atorqui, D., Alhassan, A.K., Coole, S., Hammond, J., Robinson, S. 与Sizmur, T., 2022. 生物炭对两种pH值迥异的热带城市土壤中微量元素有效性及叶菜类作物吸收的影响. 可持续粮食系统前沿（Frontiers in Sustainable Food Systems）. DOI: 10.3389/fsufs.2022.821397