Richard Taylor, Extension Agronomist; rtaylor@udel.edu
Although the weather this spring has not been kind to our state’s hay producers and has even been limiting to a degree for those pasturing animals due to the colder than normal spring, it is time to consider your forage’s need for late spring fertilizer. For the hay producers, this will need to wait until the first hay crop is removed but for those that have already managed to make a hay harvest, a late spring fertilizer application should be next on your agenda to consider.
Let’s start with the product that will almost always give you the biggest bang (profit) for the dollars you spend on it. That is agricultural limestone when used to adjust your pH to the ideal range for the forage crop that you are growing. Many producers add lime either in the fall or very early spring but if you haven’t applied any needed lime yet, now will be an excellent time to have it applied. If you haven’t checked your pasture or hay field for pH using a 0 to 4 inch soil testing depth (remember all the lime you apply will be surface applied and moves downward only about 1 inch per year so this shallower testing depth is more appropriate for pasture and hay land), you should do this immediately and apply any required lime as soon as you can.
Why is soil pH so critical? If you have legumes in the pasture or are using a mixed grass and legume as a hay crop, the legume plant requires a higher pH than does the grass crop to produce the best yields. Legumes are useful in that they fix nitrogen (N) from the atmosphere and share this N with the surrounding grass plants. That reduces your need to spend money to buy N fertilizer. Another aspect of soil pH is its impact on soil nutrient availability, especially phosphorus (P) but really for all nutrients. When the pH is in the optimum range for your soil type, the availability of all nutrients will be improved and can reduce the need for added fertilizer. In addition, the ability/quantity of the soil to hold cations (cation exchange capacity) which includes calcium, magnesium, potassium, the micronutrients, and ammonium increases.
After pH, the next important fertilizer addition will be potassium or potash (K) and P. Potassium has a tremendous impact on forages by helping them tolerate the head and possibly drought stress associated with summer weather as well as helping with stress from insects and diseases. We usually recommend that half of the needed K be put out in late May or early June and the other half applied in late August or early September. The second application helps plants with the stresses experienced during the winter months from cold temperatures and wet soils. Phosphorus can all go out in the late spring application and will help with root development as well as with energy transfers within the plant as the sun’s energy is captured by the leaves and converted into glucose and then into plant components such as cellulose and hemicellulose. Both P and K should be applied based on your soil test results and recommendations from the same 0-4 inch deep soil sample.
Finally, let’s consider N. If it’s a pasture or hay field and the legume component is more than 25% of the forage present, you possibly do not need any additional N fertilizer although yield, especially the grass component, will be increased with a small addition of N. To prevent the legume-bacteria association from reducing its fixation of N, you should limit fertilizer N application to no more than 30 lbs N/acre at any given application. If a drought seems imminent or has begun, it will be best to postpone fertilizer N applications to pasture or hay fields until after the soil is rewetted by rainfall (or irrigation, if available).
For grass hay producers, fertilizer N application will increase your yield potential as long as soil moisture levels remain adequate for vigorous grass growth. Nitrogen applications should be based on the expected yield potential of your next harvest so review your records to see what your field has for hay potential. Dr. Marvin Hall from The Pennsylvania State University found in his research that from 40 to 60 lbs N/acre are needed for each ton of expected hay production. The one caution that should be taken into account is that if dry weather occurs the higher rate of N can lead to nitrate accumulation in the grass hay crop so if you expect soil moisture to be limiting before the next hay harvest use the lower rate of N per acre per ton of expected production.