Liquid manure (slurry) is essential for feeding the soil food web with organic matter, especially in the Netherlands where solid manure is scarce. Farmers therefore rely on high-quality slurry to reduce nutrient leaching, enhance soil biology, and improve crop quality. However, manure quality varies widely due to differences in feed, soil conditions, and crop management. Farmers aim to improve slurry quality within a circular system of healthy feed, healthy cows, and healthy manure, and may also apply additional treatments such as aeration, microbial additives, or acidification. Despite its importance, the effects of manure quality on soil and crops remain poorly understood, and farmers lack clear indicators to identify the best manure for different soils and crops.