Two key outcomes were evident from this evaluation: (i) nutrient management at the whole-farm or field level requires the integration of a diverse set of management considerations and an understanding of the temporal changes that occur in the soil–plant–manure nutrient interface, and (ii) having a management plan in place that includes the collection of qualitative and quantitative information is key to making sound management decisions. Specific conclusions are:
- Additional manure application increases CP content and dry-matter yield in grass silage. However, timing of manure application appears to be more important to achieving a dry-matter yield response than amount of manure applied.
- New-seeding grass probably does not need commercial N fertilizer if the soil has historically been amended with manure.
- New-seeding grass will more likely have a higher level of nitrate N than old-seeding grass.
- Malfermented and high CP grass silages create a challenge for achieving a balanced ration because when soluble N and ammonia N are overfed there is less efficient use of metabolizable protein for milk synthesis, and when nitrate N is overfed it can be a health risk to the animal.
- Understanding the N cycling between the manure, soil, and plant provides the opportunity to utilize N available to the crop more efficiently.