Nitrogen and Phosphorus are typically the two most limiting nutrients in the soil.

If any one nutrient is too limiting, it may hinder plant growth and production, thus reducing your net yield. Nitrogen is often added to increase grass production, while Phosphorus promotes legumes. That being said, if Phosphorus is deficient in your soils, it may also limit grass growth.

Several studies on fertilizers suggest that the net pay off is almost always positive (meaning that the producer always made money from fertilizing and never lost any money).  Nevertheless, the amount of profit you make may vary with the type of fertilizer you use (Ammonium Nitrate vs. Urea) and climatic factors.  In speaking with Junior from Frontier Station out of Craig, Ammonium Nitrate fertilizer is better than Urea because it is less volatile and does not evaporate or leach as easily as Urea. You also have a larger window for application of Ammonium Nitrate and can apply it under dry conditions.

Mark Volt, District Conservationist for the NRCS Kremmling Field Office, says that fall vs. spring fertilizer applications yield similar results as far as grass growth and productivity in Middle Park. However, because Phosphorus takes longer to dissolve and move into the soil, Mark suggests that fall is better for Phosphorus application.  If applying fertilizer in the fall, you want to fertilize when soil temperatures consistently drop below 50 degrees Fahrenheit and plants are dormant. This typically happens after October 1st-15th.

Thus, it comes down to a personal preference and fertilizer type as to whether you opt for fall or spring application.

Factors to consider are cost, availability of fertilizer buggies, and time constraints. You may find that fertilizer buggies may be easier to get in the fall and you may have more time on your hands.