Solubilization and mineralization of phosphorus by selected bacterial strains in biochar enriched with rock phosphate

Abstract

Biochar-based fertilizers (BBF) are nutrient enriched biochar that may increase nutritional efficiency of plants, especially in tropical soils. Biomass impregnated with phosphates sources prior to pyrolysis increase biochar yield and carbon stability. However, when rock phosphate is added as a phosphorus (P) source, P solubility is very low and may not supply plant requirement. An environmentally friendly alternative to increase its solubility is to use selected bacterial strains that solubilize or mineralize phosphates, which has not been explored in these type of materials so far. The aimof this study was investigate solubilization and mineralization of P in BBF enriched with Bayóvar rock phosphate by selected bacterial strains. We also aimed to evaluate the agronomic efficiency of BBF inmaize(Zea mays) growth under bacterial inoculation.The BBF was characterized and its P solubility was studied in anin vitro assay using five selectedstrains: UFLA 03-09 (Acinetobactersp.), UFLA 04-155 (Burkholderiafunforum), UFLA 03-10 (Paenebacilluskribbensis), UFLA 03-116 (Paenibacillussp.) and UFPI B5-8A (Pseudomonas sp.). Based on this assay, three strains (UFLA 03-10, UFLA 04-155 and UFPI B5-8A) were chosen to test the agronomic efficiency of BBFin maize. Five doses of P (0; 50; 100; 200 and 400 mg kg-1 based on total P) from the BBF were applied. A positive control (200 mg kg-1P as triple superphosphate) was also included. Shoot dry matter, P accumulation in shoot andagronomic efficiency index were evaluated. After cultivation,soil pH, available P and activity of acid and alkaline phosphatase in soil were determined. Bacterial strains solubilized P in the in vitro assay, which was closely associated with a pH decrease and the types of organic acids produced. A significant interaction between P doses and bacterial inoculation was observed for available P in soil. Inoculation increased shoot dry matter and P doses increased shoot dry matter, P accumulation in shoot, soil pH and phosphatase activity in soil. Positive control presented higher agronomic efficiency index than BBF. These results indicate that inoculationwith selected bacterial strains combined with BBF fertilization is an inexpensive and sustainable strategy for improving maize growth and enhancing available P in soil. However, further studies must be carried out to improve the P use efficiency from low availability P sources.