Nitrogen (N), phosphorus (P), and potassium (K) are essential plant macronutrients. Many agricultural soils contain deficiency of either N, P, and or K worldwide. The use of synthetic fertilizers can be costly and unsustainable. Here, NPK enriched commercial Douglas fir biochar fertilizer (NPK/BC) was prepared using chemical co-precipitation of magnesium ammonium phosphate and magnesium potassium phosphate. NPK/BC has 43.76, 120.14, 3.79, and 34.05 mg/g of NH4+, PO43-, K+ and Mg2+ respectively with NPK ratios of 3.4, 9.0, and 0.4 respectively. NH4+, PO43- and K+ leaching in de-ionized water was pH independent (3-11). Their leaching in different water matrixes at different temperatures (5, 25, and 40oC) was investigated. NPK/BC also can facilitate heavy metal, anion, and organic contaminant removal. NH4+, PO43-, K+, and Mg2+ leaching were studied in the presence of individual species (C0 = 100 mg/L); Cu2+, Pb2+, UO22+, F-, and methylene blue as well as their removal. Marshall ryegrass greenhouse studies with different P rates of 29.70 (56.04 Kg N(total) ha-1), 29.70 (0 kg N(total) ha-1), and 59.41 kg ha-1 (56.04 kg N(total) ha-1) were performed by fixing K2O, Mg, lime, and micronutrient (frit) at 72, 22.56, 500, and 22,42 kg ha-1, respectively. Control studies were carried out with soil, synthetic fertilizers, and untreated biochar. NH4+, PO43-, K+, and Mg2+ continuous-flow fixed-bed column studies were performed for synthetic and NPK/BC fertilizers. NPK enriched biochar is a relatively cost-effective and eco-friendly nutrient source. This study provided evidence that NPK/BC could be utilized as a slow-release fertilizer.

Douglas fir biochar-based controlled release NPK fertilizers for sustainable agriculture

ACS Spring 2022

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