Phosphorous Determination in Biochar-Based Fertilizers by Spark Discharge-Laser-Induced Breakdown Spectroscopy

Biochar-based fertilizers are a new attractive alternative to P supplementation for crops, as
they can gradually release the nutrient, avoiding losses and improving soil quality. In this regard,
the evaluation of the P amount in biochar-based fertilizers is extremely important for their quality
control. Analytical techniques that require sample solubilization are not very efficient for this task,
as biochar is difficult to solubilize. Laser-induced breakdown spectroscopy (LIBS) is a promising
technique to respond to this demand, as it enables a direct analysis of solid samples, avoiding the
complicated process of sample solubilization. In this work, a novel method based on spark discharge
(SD) coupled to LIBS was evaluated for P determination in biochar-based fertilizers prepared from
three different biomasses. To overcome calibration problems in LIBS analysis, a matrix-matching
procedure accomplished by the addition of eucalyptus biochar to calibration standards was used
in experiments. This procedure minimized matrix effects and allowed us to achieve a satisfactory
accuracy even when applied to similar but different matrices. Furthermore, the developed method is
simple, fast, direct, does not generate post-analysis residues and appears appropriate for the quality
control of sustainable biochar-based fertilizers and other biochar products.