Fertilizing grass and alfalfa
If you plan on fertilizing grass hay or pasture it should be done early in the season. Also if the fertilizer can be applied right before a rain it will ensure that it gets into the soil and is not lost to the air. With grass hay it takes 25 lbs of actual N to produce one ton of hay. Usually there is at least 25 lbs of N left in the soil; however a soil test taken two feet deep is the best bet to be sure. A common recommendation for grass pasture or hay land is to add 50 lbs of N to get a three ton production or 75 lbs of N to get a four ton production. You will need good soil in the pasture to produce over three ton. If you have a warm season grass field, fertilizing should be delayed until mid-May. This is then warm season grass starts to grow. However, when you wait for warm season grasses it is very important to spread as close to rain as possible so there is not volatilization of the nitrogen.
The key with fertilizing alfalfa is not to fertilize when the field is wet. If you are out after the frost is out of the ground and the field has not firmed up you will do damage to the alfalfa crowns. It may not show up this year but it will show up next year because the damaged crowns will not over-winter and will be dead next year. A soil test to six inches will tell you what fertilizer is needed. Usually most soils will need at least 50 lbs actual of phosphorus to produce 4 to 5 tons and depending on the level of potassium in the soil, recommendations will vary from zero on high testing soil to 160 lbs actual on some lower testing soil. With alfalfa do a soil test, don’t guess. It’s always the best answer.