Summer annuals like pearl millet, crabgrass, forage sorghum, sorghum-sudans, etc. typically play a huge part in the forage system for the state of Georgia for either grazing or baleage. And fertilizing summer annual forages is a critical component of successful forage production. Proper nutrient management not only boosts yield and forage quality but also plays a key role in maintaining long-term soil health and controlling production costs. As always the forage team recommends any production system to begin with soil testing. Each soil sample should represent 5 to 15 acres, being collected in a zig-zag pattern across the field. Soil sampling will not only tell you how much phosphorus and potassium to apply in addition to recommended nitrogen applications, it will also tell you the pH of the land. Maintaining the correct soil pH is vital and liming is essential for improving nutrient availability and fertilizer efficiency. To emphasize the importance of maintaining a correct pH for the crop, you can reduce the efficacy of your nitrogen application of 35% if you pH is a 5.6 instead of a 6.2 in forages, which results in roughly a $42 loss per acre. Although lime takes 6 to 12 months to significantly affect soil pH, applying one ton per acre in every three years in addition to the recommendations on your soil sample is typically enough to offset the acidifying effect of nitrogen fertilizers.
For summer annuals grown for grazing, nitrogen should be applied at a rate of 40 to 60 pounds per acre soon after the grasses emerge. Additional applications of 50 to 60 pounds of nitrogen per acre should be made monthly throughout the summer grazing season. Phosphorus and potassium should be applied based on soil test recommendations after emergence to support healthy root development and overall plant vigor.
When summer annuals are intended for harvest, the fertilization approach changes slightly. A base application of 40 pounds of nitrogen per acre should be made at planting, followed by 60 pounds per acre after the plants are well established. An additional 60 pounds per acre should be applied after each harvest, with the exception of the final cutting. If multiple harvests are expected, phosphorus and potassium rates should be increased by 25% over the standard recommendations to replenish nutrients removed in the forage.
When using summer annuals in your production system, steps must be taken to avoid prussic acid and nitrate toxicity, which are risks associated with certain warm-season grasses, especially under conditions of drought or frost. To reduce the risk of livestock poisoning, nitrogen applications should be split, and grazing should be delayed following stressful weather events. A good rule of thumb is to wait at least 7 days after a drought-ending rain (roughly one half inch) before grazing or harvesting the crop. There are also lab tests that can be conducted to ensure an extra level of caution.
For producers aiming to reduce fertilizer costs without compromising forage quality, several strategies can be employed. Splitting fertilizer applications helps minimize nutrient losses, while increasing soil organic matter can improve nutrient retention and water holding capacity. Using GPS-guided fertilizer application can also reduce overlap and waste; even a 10% overlap can increase input costs by $50 to $70 per acre. Precision management tools, although an initial investment, can lead to significant long-term savings in labor, fuel, and inputs.
While we understand that fertilizer is expensive, it is critical to the success of your forage production. If you need assistance in making decisions on fertilizing your hayfields and pastures, contact your local county extension agent.
