Determining the required seed quantity for hay production involves balancing desired plant density against seed quality and specific field conditions. Achieving an optimal stand density maximizes forage yield and quality while suppressing weed competition. Selecting the correct seeding rate is foundational for establishing a successful, long-lasting hay field. A rate that is too low results in a thin stand prone to weed invasion, while a rate that is too high wastes money and causes self-thinning due to excessive competition.
Establishing Baseline Seeding Rates
The initial step is establishing the unadjusted, general baseline seeding rate for the chosen forage species. These rates represent the typical pounds of seed needed per acre for a pure stand under ideal conditions. For example, Alfalfa generally requires 10 to 20 pounds per acre. Common cool-season grasses like Timothy and Orchardgrass typically require 8 to 12 pounds per acre.
Tall Fescue requires 15 to 20 pounds of seed per acre for a pure stand. Legume species like Medium Red Clover fall within the range of 10 to 15 pounds per acre, while White Clover requires substantially less, often 3 to 5 pounds per acre. These figures serve as a starting point, but they must be refined based on the actual quality of the seed purchased and specific field management practices.
Calculating Pure Live Seed
Baseline rates assume the seed is 100% pure and 100% capable of germination, which is rarely true. The Pure Live Seed (PLS) calculation adjusts this figure by accounting for the percentage of the seed that will actually grow. PLS is determined by multiplying the seed’s Purity percentage by its Germination percentage, information typically found on the seed tag. For example, if a seed lot has 90% Purity and 80% Germination, the PLS percentage is 72% (0.90 x 0.80 = 0.72).
This PLS percentage represents the proportion of viable seed in the total weight. To find the actual bulk weight needed, divide the desired Pure Live Seed rate by the calculated PLS percentage. If the goal is 15 pounds of PLS per acre, and the seed lot is 72% PLS, the required bulk seeding rate is 20.8 pounds per acre (15 lbs / 0.72).
Seed coatings, common on legume seeds like Alfalfa, also affect the PLS calculation because the coating material adds weight but is not pure seed. A highly coated seed may have a lower Purity percentage, requiring a higher bulk weight to deliver the same amount of live seed per acre. Calculating PLS ensures the investment targets the number of viable seeds required for a successful stand.
Adjusting Rates Based on Site and Management
After calculating the Pure Live Seed rate, further adjustments are necessary based on site-specific factors and the intended planting method. The planting method significantly impacts the required rate because it affects seed-to-soil contact and precision. Drilling seed with a specialized drill is the most efficient method, requiring the lowest rate.
Adjusting for Planting Method
Broadcasting seed onto the soil surface is less efficient, as many seeds fail to achieve the necessary soil contact for germination. When broadcasting, the seeding rate should be increased by 25% to 50% to compensate for the lower establishment rate. Planting into poor seedbeds, such as those with high residue or loose soil, also necessitates an increased rate to offset higher seedling mortality.
Adjusting for Environmental Conditions
Environmental conditions also influence the final seeding rate. Factors like low soil fertility or marginal moisture require a higher density to ensure sufficient plants survive establishment. Phosphorus and potassium are important for root development and winter survival, and deficiencies may warrant a higher initial rate. For short-term hay production, a slightly higher rate can be used to achieve faster ground cover and weed suppression.
Adjusting for Mixed Stands
When planting a mixture of species, such as a grass and legume combination, the seeding rate for each individual component should be reduced from its monoculture rate. This reduction prevents one species from overly competing with the other, allowing both the grass and the legume to establish effectively. The final adjusted rate synthesizes the initial baseline, the PLS quality, the planting technique, and the environmental stresses unique to the field.