Extending the Growing Season to Improve Farm Nutrient Budgets.

Whole farm nutrient mass balance (NMB) assessments can be used to evaluate nutrient accumulation and related loss potential over time, and when conducted on an annual basis, allow for identification of impact of management changes on the long-term stability of farming systems. In New York, NMB assessments have been conducted for nitrogen (N), phosphorus (P) and potassium (K) for dairy farms over the past ten years, resulting in a dataset that includes 54 farms with four or more years of data. Results show that many of these farms reduced their NMBs over time while maintaining or increasing milk production per cow, indicating the effectiveness of NMB assessment as an adaptive management tool. The main driver for change in N and P balances was feed imports while adjustments in both feed and fertilizer imports affected K balances. In general, management changes that reduced the need for external feed purchases had the greatest impact on nutrient balances. In addition to implementation of precision feeding, management changes that extend the growing season for greater forage production per unit land area per year, and that result in more stable forage production in a changing climate, are most successful in addressing nutrient use and loss to the environment. In the past five years, farmers in NY have shown that a change in crop rotation on dairies to include winter cereals grown as double crops can be effective in increasing annual forage production, with up to 20% greater overall yield. More recently, replacement of corn silage by brown midrib forage sorghum as the main forage crop in rotations has shown promise, as sorghum can be planted in June and harvested by mid September, enabling timely planting of winter cereals for year round coverage of soil (erosion reduction, N and P management). We conclude that implementation of double cropping is an effective practice to address the long-term sustainability of dairy farming in the northeastern US.