T-Sum & Current Set Backs
What is T-Sum?
T-Sum stands for temperature summation. Its a tool to know when grass will be ready to start actively growing and utilizing applied nutrients. We provide resources for understanding your manure application risk, including current set backs and local T-Sum calculations.
T-Sum = 205! 3/2/2025
Manure Application Setback Distances (ft)
| January & February | March & April | May | June, July, & August | September | October | November & December |
|---|---|---|---|---|---|---|
| 80* | 40 | 40/10** | 10** | 40 | 80 | 80*** |
Spreading Regulations
*Any manure application made from November-February must have a winter spreading plan in place. Contact your Whatcom CD planner to add this to a farm plan.
**These are minimum distances and may need to be increased during un-seasonally wet periods. A big gun applicator should not be closer than 40 feet at any time of the year due to drift.
***Application during November and December is typically not necessary and must be shown to be agronomic before manure is applied. Any manure application made from November-February must have a winter spreading plan in place. Contact your CD planner to add this to your DNMP.
These guidelines apply equally to both liquid and solid manures.
