| Abstract: | Biochar produced in cost‐efficient flame curtain kilns (Kon‐Tiki) was nutrient enriched either with cow urine or with dissolved mineral (NPK) fertilizer to produce biochar‐based fertilizers containing between 60–100 kg N, 5–60 kg P2O5 and 60–100 kg K2O, respectively, per ton of biochar. In 21 field trials, nutrient‐enriched biochars were applied at rates of 0·5–2 t ha−1 into the root zone of 13 different crops. Treatments combining biochar, compost and organic or chemical fertilizer were evaluated; control treatments contained same amounts of nutrients but without biochar. All nutrient‐enriched biochar substrates improved yields compared with their respective no‐biochar controls. Biochar enriched with dissolved NPK produced on average 20% ± 5·1% (N = 4 trials) higher yields than standard NPK fertilization without biochar. Cow urine‐enriched biochar blended with compost resulted on average in 123% ± 76·7% (N = 13 trials) higher yields compared with the organic farmer practice with cow urine‐blended compost and outcompeted NPK‐enriched biochar (same nutrient dose) by 103% ± 12·4% (N = 4 trials) respectively. Thus, the results of 21 field trials robustly revealed that low‐dosage root zone application of organic biochar‐based fertilizers caused substantial yield increases in rather fertile silt loam soils compared with traditional organic fertilization and to mineral NPK or NPK‐biochar fertilization. This can be explained by the nutrient carrier effect of biochar, causing a slow nutrient release behaviour, more balanced nutrient fluxes and reduced nutrient losses, especially when liquid organic nutrients are used for the biochar enrichment. The results open up new pathways for optimizing organic farming and improving on‐farm nutrient cycling. Copyright © 2017 John Wiley & Sons, Ltd. |
