Nitrogen fertilizer value of dehydration products of urine-and pine bark mixtures

The application of human urine in agriculture has gained significant attention due to its high nitrogen (N) content. This study evaluated effects of products derived from dehydration of urine mixed with materials from pine bark (PB) on spinach growth, macronutrient uptake and micronutrients concentrations under glasshouse conditions. The products were prepared by applying urine to various PB products: feedstock (PB), biochar (pyrolysed at 350 and 650 °C) and ash, and various processes: dehydration at 45, 60 °C, and in a glasshouse. The products after dehydration at 45 and 60 °C were applied to 2 kg of soil (0–20 cm depth) at recommended N rate for spinach. The pot trial ran for 84 days with plant sampling at 6 and 12 weeks for dry matter measurements while macronutrient and micronutrients analysis were done for the combined biomass (6 and 12 weeks sampling). The residual soil samples were analysed for pH and extractable phosphorus (P). The experiment was repeated with PB products dehydrated in the glasshouse. The products increased dry matter, which was comparable to the positive control (ammonium nitrate). The urine-based products increased dry matter and N uptake of spinach. Plant micronutrients concentration were within permissible limit, although manganese was high in PB feedstock and biochar dehydrated in the glasshouse under controlled conditions. Overall, urine-derived products from pine bark show potential as alternatives to synthetic N fertilizers for smallholder farmers. However, monitoring sodium and manganese levels in plant tissue is necessary to optimise crop growth and prevent toxicity. In addition, the concentrations of these elements in the soil should be investigated.