The effect of fertilisation with digestate on kohlrabi yields and quality

Abstract

The number of biogas stations in the Czech Republic has recently increased considerably; as of 1 January 2014 some 500 biogas plants were registered of which 378 are agricultural biogas plants with installed electric energy of 392 MW. The estimated annual digestate production ranges around 7.9 mil t and the biogas stations are deployed irregularly in the regions. On that account practical problems frequently arise how to utilise the digestate effectively and/or where to apply it (in compliance with legislation -for example: The Nitrates Directive and Restrictions in the Vulnerable Areas). Considering the fact that digestate is produced during the whole year, possibilities are being sought of using it not only to fertilise arable crops but also vegetables. Whereas information on using digestate to fertilise arable crops is relatively abundant, in the case of vegetables it is vice versa (Dostál et al. 2015).Manures from stables, crop residues, wastes from the food industry, municipal wastes, and dedicated energy crops are the main feedstocks for anaerobic digestion (AD) in biogas plants. The residual product of AD, called digestate (= biogas effluents = biogas residues, or biogas slurry, when animal manures are digested), is usually used as (1) untreated control; (2) digestate; (3) digestate + phosphorus (P). The nitrogen (N) rate was the same in treatments 2-3. There were significant differences between years in all parameters. The weight of single kohlrabi bulbs in the unfertilised control was significantly lower in both years (33.1-46.9%) than in the digestate treatment (100%). Digestate supplemented with P (treatment 3) increased the bulb yield significantly by 11.0-14.3% compared with pure digestate (treatment 2). In both years the content of bulb nitrates (mg NO 3 -/kg FM (fresh matter)) was significantly the lowest in the unfertilised control (135 and 163, respectively). After digestate applications the nitrates content (mg NO 3 -/kg FM) increased significantly in both years, i.e. to 315-327 (2014) and to 486-509 (2015) compared to unfertilised control. In two years the content of ascorbic acid (mg/kg FM) did not differ among the three treatments (274-288 in 2014 and 311-329 in 2015). Digestates can be recommended for kohlrabi fertilisation prior to planting.

A Bio-Refinery Concept for N and P Recovery—A Chance for Biogas Plant Development

“…in order to increase the N recovery efficiency from the liquid fraction of digestate. (6). The liquid fraction after STR precipitation was alkalised by means of 5N NaOH, reaching a pH of 10.5.…”

“…Moreover, the pH of LFDS was adjusted to 9 by means of continuous 5N NaOH addition. At the second stage, ammonium sulphate (AS) was produced at 70 • C in the ammonia stripping installation: H 2 SO 4 vessel, stripping tower and reactor (6). in order to increase the N recovery efficiency from the liquid fraction of digestate.…”

“…Nowadays anaerobic digestion has become an increasingly important source of renewable energy. During the anaerobic digestion, organic compounds are subject to degradation, leading to the accumulation of mineral forms of N and P in the remaining digestate [6][7][8]. Digestate is usually subject to solid-liquid separation [9].…”

Distillery Anaerobic Digestion Residues as Fertilizers for Field Vegetable Crops: Performance and Efficiency in Mid-term Successions

“…Considering the main macronutrients, Möller and Müller [12] highlighted that the concentration of N can vary from 3.1% to 14%, P from 0.6% to 1.7%, and K from 1.9% to 4.3%. Experimental trials linked to the use of digestates derived from plant materials are very scarce [17][18][19][20]. Many of them refer to arable-industrial crops [21] and microalgae [22].…”

Changes of risky element concentrations under organic and mineral fertilization

“…Still, there is huge uncertainty in defining the benefits of bioenergy utilization and digestate reuse (Meyer-Aurich et al 2012). While most studies of digestates have focused on its fertility and other active impacts on agricultural production (Lošák et al 2011(Lošák et al , 2016, little attention has been paid to the effects of its application on heavy metal concentrations (Chen et al 2013).…”