Abstract
Anaerobic digestion of organic wastes produces solid residues known as digestates, which have potential as a fertilizer and soil amendment. The majority of research on digestate focuses on their fertilizer value. However, there is a lack of information about additional effects they may have on plant growth, both positive and negative. Understanding the effects of digestate on plant growth is essential to optimizing their use in agriculture and helping close the loop of material and energy balances. This greenhouse study evaluated the effects of two different digestates, a food waste digestate (FWD) and a lignocellulosic biomass digestate (LBD); a liquid fertilizer; and various combinations of fertilizer and digestates on plant growth, nutrient uptake and nutrient use efficiency (NUE) of Brassica juncea (kai choy) plants. It also evaluated potential negative attributes of the digestates, including salinity and possible biohazards. Combinations of LBD and fertilizer performed as well or slightly better than the fertilizer control for most parameters, including aboveground biomass and root length. These same combinations had significantly higher nitrogen use efficiency than the fertilizer control. Inhibitory effects were observed in 100% LBD treatments, likely due to the high electrical conductivity of the media from digestate application. Based on this research, LBD could partially replace mineral fertilizers for kai choy at up to 50% of the target nitrogen rate and may lead to increased plant growth beyond mineral fertilizers. FWD could replace up to 100% of the target nitrogen application, without causing significant negative effects on plant growth. Increasing the use of digestates in agriculture will provide additional incentives for the anaerobic digestion process, as it produces two valuable products: biogas for energy and digestate for fertilizer.
Highlights
Introduction published maps and institutional affilWith rapid urbanization and population growth, significant amounts of waste, organic waste, are generated
The unamended control treatment produced the lowest amount of biomass and was included only for nutrient use efficiency calculations
The treatments containing low to moderate amounts of lignocellulosic-biomass digestate mixed with fertilizer (LBD10 and LBD50) produced the highest amount of biomass of all the treatments, not significantly different from the fertilizer control (Figure 1)
Summary
With rapid urbanization and population growth, significant amounts of waste, organic waste, are generated. More than a quarter of the waste produced in the United. States consists of organic materials, much of which is landfilled or incinerated, leading to a multitude of environmental problems [1]. Global dependence on fossil energy has created energy insecurity in much of the world, along with significant environmental costs, including production of greenhouse gases and degradation of air quality. Anaerobic digestion (AD) is a promising technology with the capability of turning a variety of organic materials, including organic waste, into two potentially useful products: renewable bioenergy in the form of biogas and the digested solids, hereafter referred to as “digestate”, as a potential fertilizer and soil amendment [2].
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