In many regions of the world, the current trend of consolidation and intensification of animal agriculture often requires a greater dependence on purchased feed. As more animals are added to a fixed land base, and more feed is imported onto a farm, the excretion of manure nutrients can surpass the recycling capacity of local land, air, and water resources. In response to these environmental challenges, many industrialized countries have enacted legislation to control manure management and the emission of hazardous gasses from animal production systems. Research and extension agencies were allocated considerable public funding to develop and extend technologies that would assist livestock producers in meeting environmental standards. In response to dairy industry needs for practices that would facilitate manure management and compliance to water and air quality standards, transdisciplinary dairy nutrition-soil science research was initiated to evaluate relationships among the type and amount of P and crude protein (CP) in lactating cow rations, and milk production, manure chemistry, and environmental outcomes. Nutrient source-sink relationships provided the functional framework for this transdisciplinary research: dairy nutrition research was conducted to evaluate impacts of ration components (sources) on milk production (sink) and manure components (sinks), and soil science research was conducted to evaluate impacts of manure components (sources) on water (sink) and air (sink) quality. For example, unnecessary mineral P in supplements in dairy rations was found to be excreted entirely as water soluble P in manure and, after manure land application, increased soil test phosphorus (STP) levels, P loss in runoff, and the cropland area requirements in order for producers to comply to comprehensive nutrient management plans (CNMPs). Likewise, feeding CP above recommended levels increased the excretion of urea N in urine and subsequent ammonia (NH3) loss from soil after manure application. The type of forage fed to dairy cows and the tannin content of dairy cow rations also impact NH3 emission, soil N cycles, crop yield, and N uptake. Four main ingredients to transdisciplinary dairy nutrition–soil science research have been (i) an immediate and clear need for the information, (ii) the required expertise of both dairy nutrition and soil science to provide this information, (iii) the ability and willingness of scientists and other stakeholders to work together, and (iv) adequate funding.