Plant-based liquid anaerobic digestate to sustain horticultural crop nutrition

Concerns over the sustainability and economic viability of synthetic chemical fertiliser supplies have stimulated demand for suitable, more sustainable alternatives. Digestate, a by-product of biogas production, has the potential to increase plant growth and soil fertility both sustainably and effectively. Using both liquid and solid digestate presents many opportunities for securing long-term food supply, and its application to low organic matter soils has been advocated widely in broadacre agriculture. However, optimising digester feedstock to enhance the nutritional content of digestate output for both commercial and retail horticulture is an emerging area. We hypothesised that the liquid fraction of digestate could sustain tomato growth at comparable levels to existing synthetic products. Thus, an optimised plant-based liquid fertiliser, derived from the anaerobic co-digestion of grass and energy crops, was compared with general and crop-specific fertilisers at the manufacturer’s recommended concentrations. Liquid digestate must be applied in larger quantities than currently recommended, and potentially amended to sustain plant growth. Secondly, we hypothesised that the microbial component of liquid digestate benefits plant performance. Thus, we compared crop responses to unautoclaved and autoclaved forms of liquid digestate at the N concentration of a general synthetic fertiliser. We found that, at least for low doses, the microbial element of liquid digestate did not affect plant growth, suggesting that the product may be concentrated or dehydrated to reduce the environmental footprint of distribution.