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To Combat Effects of Drought on Bermudagrass, Fertility and Weed Control are Key

Posted Apr. 30, 2006

Spring is here! Most of the region has received some much-needed rainfall, and we can begin to put the drought behind us. Now is the time to get fertilizer applied and herbicide, too, if needed. This article will discuss some fertilizer management and weed control strategies that should be considered to boost introduced pasture production, especially after a drought.

First, fertilize. Bermudagrass needs fertilizer to perform well. Ideally, you soil-sampled your pastures within the last three years. If so, fertilize according to the recommendations in order to meet the livestock demand or desired yield goal. If you did not soil-test and plan on applying fertilizer, you are gambling with your fertilizer dollars. Citing a fellow soil and crops specialist, three things can happen if you do not soil-test, and two of them are bad. First, you may spend money on fertilizer you do not need because that nutrient is already sufficient. Second, you may not apply the right fertilizer or enough to correct a nutrient deficiency. Third, you might get it right. It is difficult to make fertilizer recommendations without a soil test, so, I am not going to try. Instead, I am going to briefly discuss the importance of phosphorus in bermudagrass forage production. Soil test phosphorus levels in both Oklahoma and Texas have been steadily declining for some time. If a soil is extremely deficient in phosphorus, it is likely you may only be able to use 50 percent of the nitrogen fertilizer applied. Chris Rice, area agronomist for the Oklahoma Cooperative Extension Service, has done some research to determine if degraded bermudagrass pasture can be rejuvenated using only fertilizer and herbicide. The results were interesting. He concluded that degraded bermudagrass pasture could be recovered within two years using this strategy. Nitrogen alone did not get the job done, but it did grow some "big and healthy" weeds. In most cases, the phosphorus-alone treatment did as well, if not better, than the nitrogen-only treatment. However, when phosphorus and nitrogen were applied together, bermudagrass yields improved, and when an herbicide (2,4-D) was applied with this treatment, yields more than doubled. Of course, the only way to know for sure how much phosphorus, if any, is needed, is to do what? You guessed it, soil test. In fact, if phosphorus is extremely deficient and you do not plan on applying phosphorus fertilizer, I suggest that you do not apply any fertilizer at all. Odds are, it will be more economical in most cases.

Supposing all other nutrients are sufficient, we can make some assumptions regarding how much nitrogen (N) fertilizer will be needed. Fifty pounds of actual N per acre is the minimum amount needed to keep bermudagrass healthy and vigorous. If the pasture is used for grazing only and the stocking rate is light, this rate of N may be all that's needed. Apply 80 to 100 pounds actual N per acre initially in the spring for moderate to heavy stocking rates. Any time you plan on applying more than 100 pounds of N per acre, we recommend you split applications. Noble Research Institute research showed an increase of 800 to 1,000 pounds of forage per acre by applying 100 pounds of N per acre in May and 50 pounds of N per acre in June, versus applying all 150 pounds in May. Nitrogen can be applied at any time through the growing season for additional forage production with adequate soil moisture to warrant a response.

N management is slightly different for hay production, because hay removes all the nutrients from the field. Increase your initial N application to 100 pounds per acre. If additional cuttings or grazing is planned, apply 50 pounds actual N per acre after the first cutting. It takes about 50 pounds of N per acre to yield 1 ton of bermudagrass hay, assuming all other conditions are favorable. It is key to note the importance of both phosphorus and potassium when haying. Again, a soil test is the only way to determine how much of these nutrients are needed. Potassium deficiency is quite common in sandy textured soils.

I hope you can see from the list of recommendations above how difficult it is to "get things right" without a soil test. All of the guesswork can be eliminated with a simple soil test. With the increased cost of fertilizer, soil testing is more valuable now than ever.

Weed control is going to be critical this spring following the drought. Bermudagrass has suffered greatly since last fall, and, with its lack of vigor, weeds will be competitive this spring. As mentioned above in Rice's work, bermudagrass responded best to additional fertilizer when an herbicide was added. I am not saying you need to spray every acre each year. A few weeds can be tolerated as long as they do not limit forage production. However, conditions are favorable this spring for heavy weed infestations. It is always best to properly identify weeds and spray at the right time to get the most for your money. Since everyone's situation is different, call a soil and crops specialist at (580) 224-6500 for herbicide recommendations.

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