Coconut husk biochar amendment enhances nutrient retention by suppressing nitrification in agricultural soil following anaerobic digestate application.

Jidapa Plaimart,Soydoa Vinitnantharat,Wojciech Mrozik,Kishor Acharya,David Werner,Russell J Davenport

doi:10.1016/j.envpol.2020.115684

Abstract

Anaerobic digestate and biochar are by-products of the biogasification and pyrolysis of agricultural wastes. This study tested the hypothesis that combined application of anaerobic pig/cattle manure digestate and coconut husk (CH) biochar can improve soil nutrient conditions, whilst minimizing atmospheric and groundwater pollution risks. Microcosms simulated digestate application to agricultural soil with and without CH biochar. Ammonia volatilization and nutrient leaching were quantified after simulated heavy rainfalls. Archaeal and bacterial community and abundance changes in soils were quantified via next generation sequencing and qPCR of 16S rRNA genes. Nitrifying bacteria were additionally quantified by qPCR of functional genes. It was found that CH biochar retarded nitrate leaching via slower nitrification in digestate-amended soil. CH biochar reduced both nitrifying archaea and bacteria abundance in soil by 71–83 percent in the top 4 cm soil layer and 66–80 percent in the deeper soil layer one month after the digestate application. Methanotroph abundances were similarly reduced in the CH biochar amended soils. These findings demonstrate combined benefits of anaerobic digestate and CH biochar application which are relevant for the development of a more circular rural economy with waste minimization, renewable energy production, nutrient recycling and reduced water pollution from agricultural land.

Highlights

Due to the rapidly increasing world population and urbanization, global demand for livestock products is expected to double by 2050, in Asia, Africa and Latin-America (Scholten et al, 2013)
This project was initiated as part of a UK-Thai collaborative investigation into the valorization opportunities for coconut husk (CH) biochar produced by an inexpensive oil drum kiln method that is accessible to low income farmers
After three years, the abundances of methanogens decreased. This is the first study applying chemical measurements and molecular microbiology tools in combination to report the effects of the combined application of biochar and anaerobic digestate on ammonia volatilization, nutrient leaching and nitrification

Summary

Introduction

Due to the rapidly increasing world population and urbanization, global demand for livestock products is expected to double by 2050, in Asia, Africa and Latin-America (Scholten et al, 2013). There will be a significantly higher number of livestock farms with waste generation as animal manure and slurry. These readily biodegradable agricultural wastes can be transformed into biogas through anaerobic digestion (Holm-Nielsen et al, 2009). Anaerobic digestion creates a nutrient-rich liquid byproduct known as anaerobic digestate (Holm-Nielsen et al, 2009). The digestate can be used as a bio-fertilizer and save. 2015; Han et al, 2018). Some Nitrospira species are capable of oxidizing ammonia to nitrate on their own in both, water and soil systems (Pjevac et al, 2017)

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