By Daniel Kaiser
As we approach mid-October, the question is: is there a benefit in fertilizing my pasture? Nutrient management in pasture situations can be tricky because you’re fertilizing on top of actively growing plants. While the plants continue to grow, we do not suggest a full rate of nitrogen be applied. However, if you are considering re-seeding a pasture and will till up the ground then you may want to consider application of P and K prior to tillage to incorporate the nutrients. Here are a few more tips to make your pasture fertilization more successful.
1. Adjust rates based on expected yield and species grown
Application of nitrogen should vary based on whether the pasture contains 100% grasses or a grass/legume mixture. If only grass is grown then apply N at a rate of 30 lbs per ton of dry matter expected. Typically 90-120 lbs of N per acre is enough annual N application for a grass pasture to maintain adequate growth. For grass-legume mixtures N rate is not suggested to exceed 60 lbs of N annually to reduce over competition of the grass in the mixture.
2. Time N applications to when the crop needs it
Apply nitrogen application when grasses are actively growing. Cool season grasses begin their growth earlier, so apply fertilizer in early spring. With warm season grasses, fertilize in late spring. We suggest early spring application for grass-legume mixtures. If you’re expecting four or more tons of material per acre, split apply N, half in early spring and the rest in August.
3. Evaluate P and K
Soil tests are essential when determining how much P and K to apply. Typically, we find K to be more likely limiting in pasture situations. You can apply suggested P and K rates with N before rapid plant growth or later in the season. Remember, do not apply P and K over frozen ground to reduce the risk of loss of the material to surface waters. Uptake of K in plants is not well regulated and high rates of applied K can greatly increase K uptake in plants. Excessive uptake of K can be problematic for dry dairy cattle and goats, predisposing them to milk fever. So timing of K fertilization can be an important consideration to limit high K forage.
4. Apply lime when you can incorporate
Liming of pastures is a common question we receive. While it is possible to lime an established pasture, the best time to lime is prior to when soil may be disturbed enough to incorporate the lime. This includes establishment and re-seeding of pastures. Lime neutralizes acidity in the zone where it is applied. Surface application can neutralize acidity near the soil surface but you need to incorporate to neutralize acidity in the top six inches. If lime is expensive or difficult to obtain, we suggest choosing grass and legume species more tolerant to acid conditions.
5. Consider sulfur for low organic matter soils
Our current nutrient guidelines for pastures do not include suggestions for sulfur. However, sandy or eroded soils with low organic matter may benefit from sulfur. We suggest 10 lbs of sulfur be applied annually in situations where soil organic matter concentration is 3.0% or less, especially when legumes are grown. If grasses look yellow after nitrogen or potassium application, they could be deficient in sulfur.
Source: umn.edu