A Model for Organic Matter of Fields Fertilized with Anaerobic Digestion Reactor Effluent

Willem Jan Oosterkamp

doi:10.11648/j.ajme.20210705.11

Abstract

Soil fertility in agriculture is maintained by recalcitrant organic matter in manures and crop residues that are recycled to the fields. In some countries crop residues are burned in the field and in others these are collected and burned in furnaces as a source of renewable energy. These practices reduce the organic matter of the soils which is essential for their fertility. Anaerobic digestion installations convert manures and crop residues (mainly straw) into carbon dioxide, methane and other components. There remains a residue of recalcitrant organic material. The methane is is used as a source of renewable energy. The objective of this study is to determine the reduction in soil organic matter due to the anaerobic digestion of straw and cattle manure. The dynamics of the decay process of straw in the soil has been applied to the anaerobic digestion of these substrates. The decay of the organic material in the effluent of anaerobic digestion installations recycled to the fields has been modelled and compared to the decay of the substrates in the soil, without anaerobic digestion. The few field data on the effect of the effluent of anaerobic digestion reactor show no or little variation, compared to those when the substrates are directly applied to the fields. Around 45% of the energy content of straw and manures can be used as a source of renewable energy. The contribution to the soil organic matter of recycled effluent is 85% of that of the substrates directly applied to the soil.

Highlights

Crop residues are burned in the fields
The guidelines suggest that using the effluent of AD reactors instead of straw and manure to fertilize the crops results longterm in a reduction of 50% in the SOM [17]
No information was given about the volumes of digested cattle manure and undigested raw manure distributed to the fields

Summary

Introduction

Crop residues are burned in the fields. Potassium and phosphate (fertilisers) in the ash are directly available for the crop [1]. The soil organic matter [SOM] is reduced [2]. SOM in agricultural fields consists of decaying crop residues, roots and dead organisms [3, 4]. Microbes and fungi transform this in carbon dioxide, water, and humic substances. SOM contains more carbon than global aboveground vegetation and the atmosphere combined [5, 6]

Objectives

Findings

Discussion

Conclusion