Fertilisation of permanent grasslands with digestate and its effect on soil properties and sustainable biomass production

Abstract

BackgroundDigestate may be used instead of mineral fertilisers for both arable soil or pastures and grasslands. Broadcast or splash spreading of digestate on soil surface may decrease utilisation efficiency of nutrients – available forms of nitrogen (e.g. ammonia) – due to losses by emission. This research aimed to evaluate if the novel approach of split application of digestate deeper into the soil profile of permanent grassland by injection improves multiple soil and plant quality indicators. MethodsBetween 2019 and 2021, a small-scale-plot field experiment on permanent grassland with three experimental treatments: (1) control (unamended), (2) injector (20 m3·ha-1 of digestate, applied to the soil by injection after the first and the second cut), and (3) hose (20 m3·ha-1 of digestate, applied to the soil by hose spreading device after the first and the second cut). Cumulative plant biomass yield and quality were determined throughout the experiment. In October 2021, soil samples were obtained and analysed. ResultsThe injector application of digestate to soil improved long-termed total carbon sequestration, respirations induced by L-alanine and N-acetyl-β-D-glucosamine, nitrate content and urease activity. Compared to the control, soil pH was significantly decreased due to both approaches of digestate application. Although total nitrogen content did not vary significantly between experimental treatments, the nitrification rate was assumed as moderate in the injector experimental treatment and primarily high in the hose experimental treatment. This led to increased acidification; despite high ammonium content, it hindered further nitrification and lowered urease activity at suboptimal pH. The digestate amendment improved grass biomass yield and its nutritional value, contributing to the increased theoretical methane yield from the grass feedstock of the injector experimental treatment. This is the first report to benefit from this possible agriculture management practice for digestate-based fertilisation of permanent grassland.