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Bangladesh Agricultural University (BAU)

Publish Date: 13 Jan 2021

O-aryl and Carbonyl Carbon Contents of Food Waste and Biosolid Predict P Availability in an Acidic Soil

Dr. Md. Shahinur Rahman

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Organic waste streams, otherwise known as organic amendments (OA), contain
potentially valuable nutrients which may additionally increase legacy nutrient availability
in soil. This is particularly the case for phosphorus (P) where declining reserves of
rock phosphate add an extra dimension to their utility. In acidic soils, OA have been
reported to increase P availability through the action of O-aryl and carbonyl groups
(represent organic acid compounds) by substituting previously fixed, legacy P and
forming organometallic complexes to reduce P sorption. This study aimed to investigate
if signature P (orthophosphate) and C (O-aryl and carbonyl) content of OA could be
used to predict soil P availability, to replace traditional ways of testing OA and also
for future prescriptive applications. Food waste and biosolid were the sources of OA
in this study, with pyrolysis and composting processes used to create a range of
functional groups. Nuclear magnetic resonance (NMR) spectroscopy was utilized to
identify forms of C (solid-state 13C NMR) and P compounds (solution-state 31P NMR) in
these OA. The O-aryl, carbonyl, and orthophosphate content were higher in pyrolysis and
composted materials compared to their feedstock substrate. The effect of OA addition
on soil P availability was monitored in a 110-day laboratory incubation study. Results
showed an increase in soil P availability (Olsen P) and a decrease in soil P buffering
capacity (PBC) after incubation. The increase in soil P availability was not predicted
well by the NMR-derived orthophosphate content of OA, which may be due to the
overestimation of plant-available orthophosphate content by the solution-state 31P NMR.
Furthermore, an additional increase in soil 1Olsen P (difference between observed and
expected) was obtained above the Olsen P added from OA indicating substitution of
previously fixed soil P. Both indices of P availability namely 1Olsen P (r = 0.63–0.83) and
1PBC (difference between treatment—control) (r = −0.50 to −0.80) showed strong
(but opposite) correlations with the ratio of O-aryl to carbonyl C content of OA. It was
concluded that the ratio of O-aryl and carbonyl C content of OA could be used to predict
the P availability in acidic soil.

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