Drought conditions can bring livestock producers to the point of having no pasture available and little hay. There may be late summer and fall rains providing late season forage growth. If this occurs there will be best to have fertilized pastures and meadows to get the biggest benefit out of those rains.
Fields must have adequate nitrogen, phosphorus, potassium, and soil pH to produce the most forage from the available the soil moisture. Producers who have maintained medium to high soil test levels for phosphorus, potassium, and pH will need to add only nitrogen to get good grass growth once the moisture returns. Soil low in phosphorus and potassium needs to have these nutrients added. Lime is needed where pH is low, but it will not be able to affect soil pH very much until rainfall begins.
Source of nitrogen
When selecting a nitrogen source to apply in dry weather, choose one that will not break down and evaporate. Ammonium nitrate, ammonium sulfate, diammonium phosphate, and poultry litter (with the exception of the ammonia fraction) will be stable on the soil surface until rainfall dissolves them and moves nitrogen into the soil. Urea fertilizer will break down and some of the nitrogen will evaporate if rain does not take it into the soil within a few days of application.
There are other things to consider when deciding among these fertilizers. Ammonium sulfate will acidify the soil but may result in higher quality forage in some locations. Diammonium phosphate provides phosphorus in addition to nitrogen and is the lowest cost source of nitrogen when phosphorus is needed. Poultry litter will be slow acting compared to commercial fertilizers since it has to decompose before the nitrogen is available; however, it contains other plant nutrients and organic matter.
Rate of fertilization
If a recent soil test is available use the indicated recommendations for phosphate and potash fertilization. When a soil test is not available and there is reason to believe that the soil tests low for these two nutrients, apply 24 pounds of phosphate and 45 pounds of potash per ton of expected forage. Where there is reason to believe that the soil test is medium for both of these nutrients, apply fertilizer at the forage removal rate of 12 pounds phosphate and 45 pounds potash per ton forage to ensure adequate nutrients for maximum growth.
The rate of nitrogen to use depends on forage need and what economic risks the manager is willing to take. With normal late summer and fall rainfall, 50 to 100 pounds of nitrogen per acre on pure grass stands will produce about 20 to 25 pounds of forage dry matter per pound of nitrogen applied. On soils low in organic matter, the response can go as high as 40 pounds of forage dry matter per pound of nitrogen applied. When the field has a high legume content, the response will drop to 10 pounds of forage per pound nitrogen.
Choice of fields
When using fall nitrogen fertilization, the best response will come from grass fields on the best soils. These sites are often hay meadows. Orchardgrass will respond well to late summer nitrogen applications but needs to be grazed off before the first heavy snowfall or by December to prevent loss of the forage useful to the grazing animal. Tall fescue is at its best when given late summer nitrogen and then given late fall to early winter grazing. Tall fescue managed this way will be high in sugar content and adequate in protein for dry cows and young growing cattle to gain weight on as long as there is enough forage.
Managed grazing will ensure that the livestock get the most out of the forage produced. Allow the grass stand to grow to a height adequate to ensure good root health before grazing. For bluegrass this is a height of 4 to 6 inches, and for orchardgrass and tall fescue this is a height of 8 to10-inches. If rainfall is not adequate to allow this height to be reached, then let the forage grow until late October, when grass growth stops because of day length and cool temperatures. Use rotational grazing to get good utilization and provide controlled rest for the plants between grazings. Do not allow the livestock to graze on more acreage than they can clean up in 3 to 7 days. If managing for a grass-legume mixture, graze to a 2-inch stubble to help the legume. If managing a pure orchardgrass stand, graze to a 4-inch stubble.
Risks if there is no rain
If there is good rainfall from the middle of August, there will be a good growth response to fertilizers applied in mid-August. If ther is not, the amount of forage produced will be reduced. However, there may be long-term benefits to late summer fertilization. If there is rain by October, the fertilizer will enable the plants to grow new roots and tillers. This will strengthen the plant for winter and increase production next spring, assuming that animals are not allowed to keep the plant grazed into the ground. The yield that was not produced in the fall may take the form of increased yields next spring.
Further information is available in the following WVU Extension Service fact sheets available from your county Extension office or on the World Wide Web: