Fertilization Tips For Summer Grasses

By Trey Gafnea

Spring is here! It is time to say goodbye to the cold, wet winter and to our dependency on feeding hay and other stored forages. It is time to develop fertilization plans for summer grass production, if you have not already done so.

The first step in your planning process should be soil testing. The test does not have to be from this year; however, University of Georgia Extension recommends sampling pastures at least once every three years. Hayfields should be samples every year. Sampling more often may be necessary if you are trying to improve soil fertility levels or if you are troubleshooting issues.

In addition to your soil test results you should review how your hay fields or pastures performed last year. Pertinent questions could include:

•  What was the yield last year – take into consideration weather conditions.
•  Was the stand thinning?
•  Did it have more weeds?
•  If bermudagrass, was there a prevalence of rust?
•  Was there cold damage?
• How thick is the stand this spring?

The answers to these questions as well as your soil test results can be very helpful in evaluating/developing your fertility program. Below is a discussion of the key nutrients for forage production and some of the most common issues related to them.

When planning your fertility program soil pH level and lime recommendations should be addressed first. Soil pH levels outside of the optimum range will reduce the effectiveness of Nitrogen (N), Phosphorus (P), and Potassium (K), thus effecting seasonal forage yields. Work done at the Texas AgriLife Research Center at Overton Texas demonstrated that a 0.5 increase in soil pH (from 5.5 to 6) resulted in a seven percent 7% increase in forage yield, which was worth $39 per acre. Maintaining a soil pH at 6 or above maximizes the availability of plant nutrients and maximizes forages rooting depth. These factors reduce plants stresses and encourage efficient forage growth.

Nitrogen is a key nutrient in grass forage production. It is one of our greatest expenditures for warm season grass production and also carries the greatest risk of being lost or wasted before being used by the plant. The timing of N applications and the N source used should be considered when developing your fertilization plan. Nitrogen needs to be applied close to the time it is being used to minimize loss and maximize yield response. Applying N in multiple applications throughout the growing season will help ensure efficient crop use. This type of application prevents the crop from taking up more N than it needs for growth, which can result in high forage nitrate levels that can be toxic to animals. Timely applications will also limit the risk of N losses through leaching and denitrification.

Your N source can also have a significant effect on forage yields. The gold standard of N fertilizers is Ammonium Nitrate, but it is not readily available in many cases. Common alternative sources include liquid UAN Solutions (usually 28%, 30, or, commonly 32%) or 28%, Ammonium Sulfate, Urea and Urea with an Enhanced Efficiency product. Research trials have shown that some rates of Ammonium Sulfate and some Enhanced Efficiency products may preform nearly equal to Ammonium Nitrate. Untreated Urea and UAN Solution may only provide 80-90% of Ammonium Nitrate yields.

Potassium deficiency is very common in the hay/pasture soil sample results that I see. Though not the sole contributor to bermudagrass decline, it is one of the primary causes of failed or declining stands. It’s no wonder, since every ton of Bermuda bermudagrass hay contains 30-40 pounds of potassium fertilizer compared to 50-60 lbs of N fertilizer. Unfortunately, potash applications are too often an afterthought when compared to N applications. Potassium is the key for stand persistence. It is very important for reducing leaf spot diseases, maximizing winter hardiness, and improving stress tolerance. Be sure to spilt K into at least two applications. If you are applying without a soil test, be sure to apply 1 pound of potash for every 1.0 to 1.5 lbs of N.

Phosphorus is another of the primary macronutrients. It plays a major role in key plant processes such as root development, reproduction and energy transfer. Low soil levels can cause difficulties in establishing new pastures. Phosphorus is relatively stable in most soils and can typically be applied in one application per year. Even though phosphorus levels are naturally low in Georgia, deficiencies are not frequently an issue with most of our forages. The common use of animal fertilizers and the historically common practice of prophylactic phosphorus applications have left many of our forage fields with adequate phosphorus levels. Phosphorus deficiencies can cause poor stand establishment and stunting. Some indications in grasses include dark green foliage with purple colored tiller bases.

Source:uga.edu