Adubação organomineral à base de dejetos bovinos na produção e nutrição de Urochloa brizantha cv. BRS Paiaguás

Abstract

The intensification of dairy farming, accompanied by the increasing generation of manure, poses major challenges to environmental management. In this context, the use of cattle manure as a raw material for producing organomineral fertilizers emerges as a viable alternative to the high costs of mineral fertilization. This study aimed to evaluate the agronomic efficiency of biochar and biofertilizer derived from cattle manure, combined with a mineral source, on the production and nutrition of Urochloa brizantha cv. BRS Paiaguás. The research was conducted in two stages: (i) production and characterization of the biochar and biofertilizer, and (ii) cultivation of the grass. The biochar was obtained from fresh cattle manure subjected to slow pyrolysis, then ground, sieved (0.25 mm), and used both in pure form and as granules formulated with bio-oil as a binder. The biofertilizer was produced through the anaerobic fermentation of fresh manure diluted in water. The experiment was conducted in pots under a randomized block design with seven treatments and three replications: (i) organomineral fertilizer (ORG), (ii) powdered biochar with potassium phosphate (BPO + PK), (iii) granulated biochar with potassium phosphate (BGR + PK), (iv) manure with potassium phosphate (EB + PK), (v) biofertilizer with potassium phosphate (BF + PK), (vi) powdered biochar (BPO), and (vii) mineral fertilizer (PK). The doses were determined based on 200 mg dm⁻³ of phosphorus, used as a reference for calculating the mineral source (potassium phosphate). In the combined treatments, an 80% organic and 20% mineral ratio was applied, considering the specific phosphorus content of each material to ensure equivalent phosphorus supply among treatments. The cultivation lasted 113 days, with five consecutive harvests. Evaluations included dry biomass yield and the macro- and micronutrient contents in the shoot, roots, and residue, as well as soil chemical attributes at the end of the cultivation. Based on dry biomass and nutrient contents, macro and micronutrient accumulation, average nutrient use efficiency (NUE), and relative shoot yield (compared to PK) were calculated. Data were subjected to analysis of variance, and means were compared using Scott-Knott’s test at a 5% probability level. The BF + PK treatment showed one of the highest total shoot dry biomass productions (12.75 g pot⁻¹) and residual biomass (7.41 g pot⁻¹), along with the greatest foliar accumulations of N, K, S, B, Zn, Mn, and Cu. The EB + PK treatment also showed outstanding performance, with high shoot (12.34 g pot⁻¹), root (8.07 g pot⁻¹), and residual (7.78 g pot⁻¹) biomass, in addition to promoting high macro-and micronutrient accumulations in roots and residues. Among the pyrolysis-derived products, the ORG and BPO + PK treatments showed the best performance. The organomineral fertilizer promoted intermediate shoot growth (10.72 g pot⁻¹), strong root development (7.58 g pot⁻¹), and notable accumulations of P, Ca, and Mg in leaves, and of Ca and Mg in the roots. The BPO + PK treatment produced shoot biomass similar to that of the biofertilizer, standing out for its high leaf N content. Conversely, isolated applications of PK and powdered biochar resulted in the lowest biomass production and nutrient accumulation. Overall, the combination of organic sources with PK, especially the biofertilizer, proved to be an effective strategy to enhance the productivity and nutritional status of Paiaguás palisadegrass, while contributing to the improvement of soil chemical attributes.