Table 1.

Screening of factors affecting the solubilization of Araxá rock phosphate by Aspergillus niger FS1 in a solid-state fermentation with sugarcane bagasse as substrate

Factor	Low level (−1)	High level (+1)	Effecta
Sucrose (mg g−1)b	25	50	0.686*
Mineralsc(ml g−1)	0	1	0.104*
Initial pH	Unadjusted (4.6)	7.0	0.044
Moisture (ml g−1)	5.7	8	−0.360*
Temperature (°C)	25	30	−0.054
Incubation time (days)	7	13	0.014
Inoculum size (conidia flask−1)	105	107	−0.030
Rock phosphate (mg g−1)	15	45	0.244*
Methanol (ml g−1)	0	0.05	−0.022
Biochar (mg g−1)	0	100	0.390*

*Significant by the t test (P < 0.05).

^aEffect = m₊ – m_– (m₊ and m₋ are the mean of solubilized P for the high and low level of each factor, respectively).

^bValues are expressed per gram of dry sugarcane bagasse added at the beginning.

^cA solution of minerals was used (adapted from Czapek's medium) (g l⁻¹): MgSO₄.7H₂O, 3; KCl, 3; FeCl₃.6H₂O, 0.108.