Improved manure management moves trade-off and synergy relationships among environmental indicators in desirable directions

Dairy production systems with a high stocking density are strongly dependent on external feed resources and concentrate nutrients in manure on a small surface area, thus causing environmental challenges. Both improved manure management and integration of crop-dairy production have been proposed as ways to reduce nutrient losses and improve sustainability of intensive dairy production. However, the potential interactive relationships between these two options are rarely investigated. This study aimed to investigate how different manure management technologies influence nutrient losses at manure management and farm levels and how manure management impacts farm multi-objective optimization results for more integrated crop-dairy production. A whole farm model (FarmDESIGN) extended with a manure management module (FarmM3) was used to simulate an intensive mixed crop-dairy farm with a herd of 66 cows and 9.6 ha of crop area. The optimization aimed to improve farm environmental performance, increase feed self-sufficiency and food production. The results showed that individual manure management technologies were insufficient to reduce nitrogen (N) losses from manure management chains due to compensatory losses, whereas combinations of slurry solid-liquid separation, covered storage of solid and liquid fractions, and improved manure application could remarkably reduce N losses by 46 to 58 % and increase manure N use efficiencies by more than 30 %. Improved manure management did not influence total N losses at farm level without decreasing livestock density. Multi-objective optimization showed that improved manure management did not eliminate trade-offs or synergies among objectives but did affect the positions and the slopes of the solution frontiers between objectives. Differences between solution frontiers of alternative farm configurations in terms of N volatilization, soil N losses and soil organic matter (OM) balance indicated that manure management chains (MMCs) could be designed effectively to optimize these objectives. This study confirmed the value of improved manure management and integrated crop-dairy production in reducing N losses and improving farm nutrient use efficiency. For intensive dairy farms with limited land availability, future studies should focus on recoupling crop and dairy production at regional scales to create more sustainable and resilient food production systems. • Improved manure management and crop-dairy integration enhance nutrient circularity in intensive dairy farms. • Combining manure technologies greatly reduces N losses. • Manure management optimizes N volatilization, soil N losses, and soil organic matter balance. • Improved manure practices alone are insufficient to address N surplus in high-density dairies.