Optimizing management of organic inputs to improve biomass production and nitrogen efficiency in Danish organic cropping systems

Summary

Organic farming and the use of organic amendments are widely recognized as sustainable strategies to minimize environmental footprints in agricultural production. However, improving nutrient use efficiency and obtaining higher yields remain key challenges in organic cropping systems. To explore the best practices to optimize the management of organic inputs in organic systems, a long-term experiment CROPSYS, was established in Denmark in 1997. The experiment includes three cropping systems growing similar crops: a conventional rotation (CGL) receiving mineral fertilizers including three cereal crops and lupine-barley intercrop as a grain legume, and two organic rotations with either N-fixing grain legume (OGL), or grass-clover as green manure (OGM). The organic systems were with or without the application of digested manure. The three systems were also designed with and without cover crops. Here, we will present the results from the latest 4-year rotation cycle (2019–2022) together with a historical overview, and share the innovative use of grass-clover-based digestate from biogas production as a renewable green manure in Denmark. The results showed that the inclusion of a green manure crop increased the yields of subsequent crops (spring wheat and winter rye) in organic systems, whereas it had a higher risk of nitrate leaching. Cover crops had slight effects on crop yields but significantly reduced nitrate leaching in both organic and conventional systems. To maximize clover’s value, it was used to produce bioenergy (biogas), and the digestate was in turn applied to the field as biofertilizer. By exploring the innovative use of plant-based fertilizer, we are optimizing Danish organic cropping systems to improve nutrient use efficiency and narrow the yield gaps compared to conventional systems, while reducing climate impact.