Performance of ash from Amazonian biomasses as an alternative source of essential plant nutrients: An integrated and eco-friendly strategy for industrial waste management in the lack of raw fertilizer materials

The increasing use of Amazonian biomass as a bioenergy source has contributed to the increased demand for fertilizers and the production of a large amount of ash. In addition to facing the challenges of an insufficient supply of agricultural inputs, the Amazon region has also faced problems in managing industrial wastes, which are not well characterized and for which few recycling options are available. Within this context, this study aimed to expand the knowledge regarding the use of Amazonian biomass ash, for which an integrative system between bioenergy and fertilizer production and waste management was proposed. This study evaluated ash applied as an alternative fertilizer, focusing on the availability and uptake of nutrients and heavy metals in acidic soils and the P dynamics using ³¹P-NMR. Three soils with different SOM values were treated with one of three doses of mineral fertilizer, namely, ash (35 Mg ha⁻¹), phosphate fertilizer (2 Mg ha⁻¹), or a mixture of ash and phosphate (35 and 2 Mg ha⁻¹, respectively), and Avena sativa was grown to verify plant availability and the treatment effect on growth. The experiment was conducted for 60 d in a growth chamber. The ash application in pure form and mixed with phosphate slightly increased the pH (0.3–0.5 unit) and promoted significant increases in the availability of P (∼212%), Ca (∼165%), Mg (∼110%), and K (∼32%). In SOM-rich soils, the high microbial activity favored the transformation of inorganic P into organic P (2–21%), preventing fixation. The ash applications promoted positive effects on biomass production (∼62%) and increased the uptake of P (∼306%), Ca (∼181%), Mg (∼131%), and K (∼38%). Thus, Amazon biomass ash could be an alternative fertilizer source, representing a sustainable option for local socioeconomic development and the establishment of a circular economy system.