Optimization of Aspergillus niger rock phosphate solubilization in solid-state fermentation and use of the resulting product as a P fertilizer.

Gilberto De Oliveira Mendes,Nikolay Bojkov Vassilev,Nina Morena Rêgo Muniz Da Silva,Ivo Ribeiro Da Silva,José Ivo Ribeiro,Thalita Cardoso Anastácio,Maurício Dutra Costa

doi:10.1111/1751-7915.12289

Abstract

A biotechnological strategy for the production of an alternative P fertilizer is described in this work. The fertilizer was produced through rock phosphate (RP) solubilization by Aspergillus niger in a solid-state fermentation (SSF) with sugarcane bagasse as substrate. SSF conditions were optimized by the surface response methodology after an initial screening of factors with significant effect on RP solubilization. The optimized levels of the factors were 865 mg of biochar, 250 mg of RP, 270 mg of sucrose and 6.2 ml of water per gram of bagasse. At this optimal setting, 8.6 mg of water-soluble P per gram of bagasse was achieved, representing an increase of 2.4 times over the non-optimized condition. The optimized SSF product was partially incinerated at 350°C (SB-350) and 500°C (SB-500) to reduce its volume and, consequently, increase P concentration. The post-processed formulations of the SSF product were evaluated in a soil–plant experiment. The formulations SB-350 and SB-500 increased the growth and P uptake of common bean plants (Phaseolus vulgaris L.) when compared with the non-treated RP. Furthermore, these two formulations had a yield relative to triple superphosphate of 60% (on a dry mass basis). Besides increasing P concentration, incineration improved the SSF product performance probably by decreasing microbial immobilization of nutrients during the decomposition of the remaining SSF substrate. The process proposed is a promising alternative for the management of P fertilization since it enables the utilization of low-solubility RPs and relies on the use of inexpensive materials.

Highlights

Phosphorus (P) is one of the most limiting elements for crop production in most soils
An initial screening revealed that the quantity of P solubilized by A. niger is affected by the level of biochar, rock phosphate (RP), sucrose and water added to the medium
By applying the sequential methodology proposed by Box and Wilson (1951), a maximum of 8.6 mg P g−1 was reached with the combination of 865 mg of biochar, 250 mg of RP, 270 mg of sucrose and 6.2 ml of water per gram of sugarcane bagasse (Fig. 1)

Summary

Introduction

Phosphorus (P) is one of the most limiting elements for crop production in most soils. The main natural P reserve is composed by apatite [Ca5(PO4)3(F,Cl,OH)] rock phosphates (RPs), from which soluble fertilizers are obtained mainly by treatment with strong acids This process requires high energy input, besides causing an almost complete dissolution of the ore, which results in the release of undesirable contaminants into gas streams, byproduct streams, and into phosphate products (Goldstein et al, 1993). PSMs can be applied directly to the soil together with poorly soluble P sources (Jain et al, 2010), such as RP, or used in in vitro systems to produce high-solubility P fertilizers from RP (Vassilev et al, 2014) The latter option allows the control of the variables that govern microbial RP solubilization, something difficult to attain in the soil. In such in vitro systems, the fungus A. niger, known by its high ability to produce organic acids, has been widely applied for RP solubilization in submerged or solid-state fermentations with a range of substrates (Vassilev et al, 1997; 1998; 2014; Mendes et al, 2013a)

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