Transformation of Phosphorus in Speciation and Bioavailability During Converting Poultry Litter to Biochar

Wei Li,Xionghan Feng,Mingxin Guo,Weiping Song

doi:10.3389/fsufs.2018.00020

Wei Li, Xionghan Feng + Show 2 more

Open Access

https://doi.org/10.3389/fsufs.2018.00020

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Abstract

Converting poultry litter (PL) to biochar and applying the biochar to cropland as a soil amendment may be a best approach for recovering nutrients from solid biowastes while minimizing the nutrient runoff losses from the treated field. To evaluate the potential of PL-derived biochar as a slow-release phosphorus (P) fertilizer, the speciation, mobilitylability, and bioavailability of P in PL and the derived biochars were examined and compared. Raw PL and its derived biochars through 300–600°C slow pyrolysis were analyzed for total P (TP), inorganic P (IP), and organic P (OP) contents. The TP was fractionated into readily, generally, moderately, low, and non-labile pools by sequential extraction with different solutions. The TP was further assessed for bioavailability using batch extraction by water, Olsen, Bray-1, Mehlich-3, and 1 M HCl extractants. The P species in biochars were characterized using solid-state 31P nuclear magnetic resonance (NMR) techniques. The results indicate that during pyrolysis OP in PL was transformed to IP and water-soluble P to low labile forms such as hydroxyapatite and oxyapatite especially during pyrolysis, initially to polyphosphate-P and subsequently to orthophosphate-P at higher temperature. Orthophosphate-P was the predominant form in biochar, with products from higher pyrolysis temperature demonstrating reduced labile P pools yet enlarged low to non-labile fractions. Bray-1 and Mehlich-3 were appropriate extractants for evaluating the immediate to medium-term available and the long-term available P in biochar, respectively. Converting PL to biochar through 450°C pyrolysis significantly reduced the water-soluble proportion and the lability of P but did not compromise the long-term P bioavailability, resulting in a P-enriched, slow release soil amendment that would minimize the P runoff risks following field application. The promising results need to be further validated in soil-biochar-plant systems.

Highlights

IntroductionPoultry production (domestic fowl rearing for meat and eggs) is a crucial economic activity in most countries to furnish affordable diet protein and suppress hunger
Poultry production is a crucial economic activity in most countries to furnish affordable diet protein and suppress hunger
When the pyrolysis temperature was increased to 500◦C and above, the “nomial” proportion of inorganic P (IP) decreased slightly from the peak value of nearly 100 to 96.6% in C500 and to 89.2% in C600 (Table 1)

Summary

Introduction

Poultry production (domestic fowl rearing for meat and eggs) is a crucial economic activity in most countries to furnish affordable diet protein and suppress hunger. Intensive and concentrated bird rearing, generates vast volumes of litter waste (mixture of feces, sheddings, and bedding materials) that requires appropriate disposal (Bolan et al, 2010). Phosphorus in Poultry Litter Biochar (K, ∼38 g kg−1) (Guo et al, 2009a) and is predominantly disposed of through land application as an organic fertilizer. Up to 50% of the P in PL is water extractable (Dou et al, 2000) and can be rapidly released into the soil water via rainfall following land application (Guo et al, 2009b). To reduce the risks of P runoff from land-applied PL, it is critical to decrease the P water extractability and release rate of the organic fertilizer

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