Soil testing is the foundation of a sound fertility program for pastures and hayfields. Soil testing can be done in either spring or fall on hayfields and pastures; however, fall is generally preferred for a couple of reasons. Sampling in the fall allows time for lime applications to react before the next growing season and gives producers more flexibility in planning fertilizer applications.
Soil sampling is typically recommended at least every 3-4 years. More frequent sampling (every two years) can prevent over-application of fertilizer or manure and increase yields by revealing exactly which soil nutrients are too low for optimum productivity. This is especially valuable when fertilizer prices are high.
Collecting a representative soil sample
- Use a soil probe if possible (We have probes in both offices for producers to borrow). A shovel or spade may also be used, but avoid “pointed” samples that over-represent the surface layer.
- Combine 15–20 cores into one composite sample for each uniform area (≤40 acres, or ≤10 acres in variable fields). Keep separate samples for areas with different crops, forages, or soil types. The goal is to capture variability within the fields.
- Avoid contamination by using clean equipment and containers.
Sampling depths
- pH evaluation: 3-4 inches
- mobile nutrients (nitrogen and sulfur): 24 inches
- Immobile nutrients (phosphorus and potassium): 6 inches
Why soil pH matters
Soil pH is one key soil property for forage production, especially with legumes. The optimal pH level is 6 to 7, depending on the forage species.
- Nutrient uptake can be reduced if the soil pH is too low or too high.
- Smooth brome grass and tall fescue perform best in the pH range of 6.0 – 7.5, but can handle pH down to 5.
- Legumes, especially alfalfa, require a near-neutral pH (~pH 7). A low soil pH reduces nodulation and nitrogen fixation in legumes, such as alfalfa and clover.
- Aluminum toxicity can occur at low soil pH.
If liming a new pasture, it is important to apply the lime 6 to 12 months before planting. Finer lime materials with a high effective calcium carbonate (ECC) value will react more quickly. Fields being prepared for alfalfa should also be evaluated for phosphorus and potassium, with any corrections made before planting.
Alicia Boor is an Agriculture and Natural Resources agent in the Cottonwood District (which includes Barton and Ellis counties) for K-State Extension. You can contact her by e-mail at aboor@ksu.edu or calling 620-793-1910.
K-State Extension is an equal opportunity employer and provider. Kansas State University, County Extension Councils, Extension Districts, and U.S. Department of Agriculture Cooperating.