Digestate from biogas production – precious fertilizer for organic agriculture

Organic agriculture has a vision of achieving ecological, social and economic sustainability. To achieve the vision, organic agriculture is guided by a number of principles. One is to economize on finite resources and reduce the environmental impact through more efficient cycles of plant nutrients. The lack of organically certified fertilizers has been significant and threatens the plant nutrient supply at organic crop farms without access to manure. At the same time, organic agriculture faces the challenge of achieving higher and more stable production levels and increased productivity.

Building the intensification on increased introduction of plant nutrients via conventional manure and society's organic residues has their risks in terms of added value with organic production and consumer confidence in organic food. Instead, we want to investigate the potential for intensification in organic production. Farm-based biogas production is often emphasized as a resource-efficient method of producing bioenergy on and getting a fertilizer, the digestate, with nitrogen in a form that can be utilized efficiently. It is also emphasized as a method to better distribute plant nutrients between animal and crop farms. However, there is little knowledge about farm-based biogas production and whether plant nutrient utilization becomes higher. In reality, the management of the digestate is crucial, which has consequences for the environment as well as for the farm's economy and productivity.

Therefore, we want to identify and analyze this on 4 different organic farms with biogas production and use of digestate. However, there is no knowledge of the added value that is important for the agricultural company and how these are valued by the farmer. It is difficult to obtain a high nitrogen utilization rate in crop cultivation when using solid manure or green manure from grass crops, which reduces the harvesting level. In theory, nitrogen utilization in these organic materials could increase with digestion, which gives a liquid digestate with a high proportion of plant-available nitrogen. A liquid fertilizer can also be dosed and spread with precision technology in crop production. However, the digestate has pH 8, which increases the risk of ammonia losses during handling, compared with manure and grass crop. We do not know how the residue is handled in practice and what the consequences are for the environment. In this project, we therefore want to explore various possibilities in organic production to increase energy efficiency, utilization of plant nutrients and improve the farm economy by farm-based biogas production in order to achieve sustainable agriculture.