The manuring principles in ancient China from the perspective of the San Cai theory

The application of fertilizer is an important means of farmland management in both the past and the modern society, which is of great significance to increase food yield and improve soil structure to achieve sustainable development. Even in modern agriculture, how to scientifically and effectively apply fertilizers while reducing environmental pollution is still a key problem to be solved. China has a long history of farmland management theory and practical experience, and offers valuable insights through historical literature. Although research has revealed manuring practices across regions like Europe, Asia, and Africa since the Neolithic periods, the guiding principles remain insufficiently understood. Here we examine Chinese fertilization-related texts, highlighting principles of past fertilization according to time, soil, crops, and human effort, anchored in the San Cai theory (Heaven, Earth, and Humanity). Ancient farmers had already understood the importance of applying targeted fertilizers at different stages of crop cultivation and adjusting fertilizer application based on seasonal rhythms. They knew how to apply fertilizers according to the soil characteristics influenced by both zonal and non-zonal factors, and could adjust fertilizer types and application techniques to suit the specific needs of different crops. Over time, the role of humanity within the fertilization system became increasingly emphasized, encompassing both human labor and the harmonious unity between individuals and society. This reflects the deepening integration of the San Cai fertilization framework. By revisiting these practices, this study helps fill the gaps in our understanding of prehistoric land management and provides valuable insights for advancing sustainable agricultural development in diverse ecological and cultural contexts. The emphasis on organic fertilizers, nutrient cycling, and soil conservation in ancient China presents a sustainable model for contemporary agriculture, offering more eco-friendly and efficient solutions to issues such as soil degradation, nutrient imbalances, and the overuse of chemical fertilizers.