Many hay producers across the state have completed or are in the process of completing their first cutting of the year. One of two best times to topdress maintenance fertilizer on hay is right after the first cutting. The other top choice is in early fall. Remember that hay crops will remove about 50 lbs of K2O and 12 lbs of P2O5 per ton of dry hay harvested.
Fertilizer can be topdressed on hay or pastures at any time during the growing season, but right after the first cutting and early fall provide times when the soils are usually firm enough to support fertilizer spreading equipment and the nutrients are applied to actively growing plants when they are most needed.
A recent soil test should be the guide for what nutrients to apply and how much. If nutrient deficiencies are suspect, then tissue tests can be helpful in diagnosis along with the soil test values. Where high rates of phosphorus and potassium are recommended, there is an advantage to splitting the application, with half applied now after the first harvest and the remainder applied in the fall.
The Ohio State University Extension has an Excel tool to help you determine the right rates to apply based on your soil test report. The OSU Fertility Recommendation Calculator and a user guide are available at https://forages.osu.edu/forage-management/soil-fertility-forages.
Strategic applications of nitrogen might be needed on pure grass hay and pasture stands. Moderate amounts of nitrogen (30-50 pounds N/Acre) can be applied in June through early July after the first cutting or after the spring flush and reproductive stages of the cool season grasses is over in pastures. This application will stimulate summer hay growth or pasture grass growth that can be stockpiled for use when pastures slow down later in the season. This application should be limited in acreage for pastures, based on how much grass growth is needed to carry the herd or flock.
Be aware of the forecasted weather conditions when applying nitrogen. While moderate rainfall will incorporate most sources of nitrogen when topdressed, be mindful when predicted rainfall exceeds 1 inch which increase potential losses of nitrogen into downstream water sources.