Agronomy Notes

May 5, 2000

Contents

RICE

Dr. Joe Street

Rice planting this season is about 10 days behind normal; with reduced acreage this year, producers should be able to plant without significant problems. Mississippi usually plants a little early, and this later planting should improve emergence and increase efficacy of herbicides, assuming the temperature increases.

Fertility timing is one production practice that is changing. For the past several years, nitrogen fertility has been somewhat routine because only one variety was grown on most of the acreage. With the introduction of three new varieties, fertility requirements are changing. Proper rates and timings of plant food are essential for high rice yields and with Delta soils, nitrogen is the nutrient most lacking. Nitrogen requirements for rice depend on the cropping system and the variety being grown.

During the development of the rice plant, you may use ammonium or nitrate forms of nitrogen. Ammonium nitrogen is relatively stable in a flooded environment and is more effective than nitrate nitrogen during the early stages of rice development. For preflood application, urea or ammonium sulfate is preferred over nitrate fertilizer. You may use ammonium nitrate or urea at midseason with equal effectiveness. On areas where soil pH is high or organic matter is low, such as cut areas, you may need ammonium sulfate.

Apply preflood nitrogen to dry soil; however, this is not always possible. If you cannot apply nitrogen to dry soil, establish a 2- to 4-inch flood, with little or no water running over the gates, and apply about 30 pounds of nitrogen (65 pounds of urea) into the flood. Avoid pumping for 2 to 3 days or hold pumping to a minimum. Apply another 30 pounds of nitrogen into the flood 7 days later and another 45 pounds in another 7 days, or when nitrogen deficiency symptoms begin to appear.

When rice follows rice or when a substantial amount of organic material is incorporated into the seedbed, 50 pounds of urea or 100 pounds of Ammonium sulfate (if there is a sulfur requirement) may be applied to two to three leaf rice to stimulate growth and reach flood stage earlier.

Research data show that the new varieties Cocodrie, Priscilla, and Wells respond to more preflood fertilizer than Lemont. For these varieties, before the initial flood, apply two-thirds of the total amount of the nitrogen that will be used for the growing season. The current recommendation is to apply 180 pounds of nitrogen on heavy clay soils. This does not include the 20 pounds applied to 2- to 3- leaf rice. The remaining one-third should be applied at midseason. This application may be split or applied as a single application depending upon the applicator. Do not apply more than 200 pounds of nitrogen per acre to these new varieties. Applying two-thirds of the fertilizer preflood will decrease the potential for kernel smut but it will not eliminate that risk. It is probably a good idea to plan to use a fungicide at the late boot stage of growth for smut control on Cocodrie and Priscilla. With Lemont, the 50/50 fertilizer split is still the recommended application method.

The Mississippi Rice Promotion Board has funded a project to evaluate nutrient requirements on deep-cut, land-formed fields. These results should be of great value in improving yields on first-year land-formed fields. We are also continuing to evaluate the benefits of chicken litter on cut land and how much is required to see that benefit.

The new addition of the Mississippi Rice Growers Guide has been published and may be obtained from your county Extension agent or the Northwest District Extension office at Stoneville.

SOIL TESTING

Dr. Keith Crouse

Samples in the Soil Testing Laboratory at Mississippi State have slowed down, and the staff is currently caught up with those submitted for soil analysis. The lab this spring averaged a 3- to 5-day working time to provide an analysis once the sample was received. If you have a client in your county who has submitted a soil sample and it has been 5 to 7 days since it was mailed, please call us at 662-325-3313 because the soil analysis probably has been completed.

WARM-SEASON PASTURE MANAGEMENT

Dr. Malcolm Broome

Warm-season perennial grasses (mainly bermuda and bahia) are the forages best suited to Mississippi's climate and are the most productive. Management for increased forage quality and quantity is especially important with these grasses. Many times the energy value of these grasses barely meet the requirements of the beef animal during the season. A one-percent increase in digestibility or energy can result in a five-percent increase in animal performance. Variety selection, proper grazing, proper fertilization, and weed control will impact pasture quality.

Quite often new grass varieties are released because they produce more pounds of forage or hay per acre than other varieties. It is more important, however, to know when this increased production occurs and what quality the grass contains. For example, research shows Tifton 9 Bahiagrass produces more pounds per acre during the growing season than Pensacola Bahiagrass does, but quality is the same. Warm-season grasses vary in quality during the growing season. These grasses are highest in quality early in the season and decline from late June through August. This decline in quality in midsummer can result in low animal gains or low-quality hay.

The actual beginning and termination of growth of bermudagrass is controlled by temperature and day length. Night temperatures below 60 degrees Fahrenheit and less than 13 hours of daylight per day cause bermudagrass growth to decrease or even stop. Additionally, growth is a response to nitrogen fertilizer and rainfall occurring during the warm months, which causes high and low production periods.

Proper fertilization will improve plant growth. A ton of grass with 10 percent crude protein contain about 50 pounds of nitrogen, 10 pounds of phosphorous, 40 pounds of potassium, and varying amounts of other chemical elements needed for growth. A ton of forage will not be produced if any of these grass nutrients are lacking. Higher yields need additional nutrients to produce at an economical level.

Adequate rainfall and a long growing season in Mississippi favor weed growth in pastures. Fertilization will increase weed growth at the expense of grass production. Summer weeds frequently emerge and begin growth earlier than do warm-season grasses. Data from demonstrations in improved pastures show 2 to 7 pounds of grass were produced for each pound of weed controlled.

Proper management of warm-season pasture grasses should result in uniform, high-quality forage to meet the nutritional needs of livestock. Pastures must be considered more than minimal-input crops to be used to their fullest potential. Contact your Mississippi State University Extension Service county agent for more information on managing your summer pastures.

SOIL AND NUTRIENT MANAGEMENT

Dr. Larry Oldham

The updated Section 4 of the Natural Resource Conservation Service Field Office Technical Guide was submitted to its staff at the end of March. The much-debated Nutrient Management Code 590, including the Phosphorus Index, was included. The complete section is available on the Internet through the Mississippi NRCS homepage.

As reported earlier in Agronomy Notes, if it is not a livestock farm meeting a permit requirement, use of the 590 guidelines is on a voluntary basis, unless there is a nutrient-management component in a government cost-share program.

SOYBEANS

Dr. Alan Blaine

Recent rains caused a lot of concern about the status of planting progress. Although rains did delay soybean planting in many areas, it often is the approach before planting that has a major influence on when growers are able to get started.

Last fall a lot of soybean-land preparation was accomplished. Once fields were shaped up or where fields were in good shape following harvest, much of the state's acreage was a prime candidate for reduced tillage or a minimum amount of field trips.

Every year the scenario unfolds. For those who put out burn-downs early, they were in good shape. For those who waited on that window to till a field late spring or waited late on a burn-down, the recent rains became a major factor influencing their plans.

Although tillage is effective at destroying vegetation, so is a well-planned burn-down program, and there comes a time when one or the other has to take place.

Burn-downs are a tool that should be used more often than they are, and they need to be used early. Calls concerning burndowns are usually not about small, easy-to-control vegetation but about large, troublesome weeds such as dock, smartweed, ryegrass, and primrose. In addition, these calls often come in after these weeds have gotten extremely large and the producer is close to planting, imposing some planting restrictions on some excellent materials.

As you consider the use of burn-down herbicides, there is one major disadvantage, drift. In most cases, there is no reason to experience this problem. The way to avoid drift is to apply burn-down herbicides early before trees begin to leaf out and other crops emerge. You can control this problem but you cannot do it the way some acres are being treated today.

The objective of a burn-down program is nothing more than a trade-off for tillage. Will it save you money? That all depends on what you use and when you get it out. If you want to have better control over planting dates, however, burn-down herbicides have a place on most acres in Mississippi. I am not telling you that you need to no-till; I am suggesting growers need to keep vegetation from getting too large, causing more intensive tillage when that time finally comes.

Live vegetation can place you into two scenarios. First, in a dry spring it can pump a lot of precious moisture out of the seed zone. Secondly, under cool, wet conditions, live vegetation will keep fields cooler and wetter longer, not to mention possibly providing a home for some unwanted pests.

Other points to consider with a burn-down are planting restrictions and drift. As you wait later, many of the materials that allow producers to broaden the spectrum of a base program such as Roundup or Touchdown, materials such as Clarity, Goal, Harmony Extra, and 2,4-D have planting restrictions associated with their uses. Used early, you can avoid these concerns.

Some of the most successful burn-down herbicides are those applied in late January/early February. Put out at this time, they cost less and are much more affective on troublesome weeds. The vast majority of winter vegetation has emerged at this time and when a residual type material is added, fields can stay weed-free for an extended period of time.

Without advanced planning (particularly when the weather does not cooperate), it becomes quite difficult to avoid problems. Think about applying burn-downs early before corn begins to emerge. In all reality, after other crops are up and growing, growers need to exercise extreme caution when putting out some materials due to the possible end result. Even putting forth your best effort is often not enough as evidenced by problems observed statewide this year.

Caution growers to calibrate planters. Base calibrations on seed per foot row, not pounds per acre. When you consider pounds per acre, the only way most will determine their planting rate is after they have completed planting a known size field or the entire crop for that matter. One reason to point out the need for calibration is the fact that seed size is quite variable this year. The main reason is due to the dry year in 1999. Be sure to check planter settings for every variety and even when changing lots within a variety. This may seem like a lot of trouble, but it can translate into a cost savings most producers will appreciate. Remember. We tend to overplant. Do not let seed size deceive you this growing season. Pay attention to seeding rates, and do not overplant; with good growing conditions (precision placement, high quality seed, proper seed treatment, etc.) 100 percent emergence is not inconceivable.

Corn

Dr. Erick Larson

Herbicide drift - A tremendous number of off-target herbicide drift problems on corn have occurred this spring. Corn planted during the warm, dry conditions of early March emerged quickly, and unfortunately, thousands of acres were destroyed by careless burn-down herbicide applications. Corn injury from herbicide application was often documented more than one mile away from the target field. Do not apply any herbicides during conditions conducive to off-target drift. Extreme caution is required when susceptible crops are downwind. Increasing acreage of herbicide-tolerant crops may also raise potential for corn injury from herbicide drift during May as well.

Diagnosing drift injury - A banding pattern, which is distinguishable from soil-active herbicide injury, normally results from a slight Roundup/Touchdown herbicide drift on young corn. Lower leaves show contact injury, either chlorosis (white tissue) or necrosis (dead tissue), on much more of the leaf surface, while contact injury on subsequently higher leaves is closer to the leaf tip. The banding pattern results from higher leaves being enclosed within the whorl when the drift occurred. This banding pattern is more evident when injury is relatively slight, so little herbicide translocation occurs within a leaf or in new leaves. Roundup/Touchdown injury may also result in purple coloration, normally associated with the leaf midrib, contrasting with phosphorus deficiency.

Assessing Crop Injury - You may assess crop injury from Roundup/Touchdown drift by observing the degree of chlorosis in new leaves emerging from the whorl over several days, at least 2 weeks after the drift occurred. It takes at least 10 to 14 days for the herbicide to translocate to the growing point, which is underground, and produce injury symptoms in the whorl. Cool growing conditions lengthen the interval required to evaluate plant health, because growth rate slows dependent upon temperature, particularly when soil temperatures are below 55 degrees Fahrenheit (as they were in early April to mid-April). Plants with new leaves that are entirely chlorotic and not emerging from the whorl, indicating the growing point is severely stunted, likely will not recover and will require replanting. Plants with leaves emerging from the whorl and showing moderate chlorosis and substantially reduced width are moderately injured. Careful evaluation over the next week is required to make a replant decision. A condition with plants with new leaves emerging from the whorl showing no chlorosis, indicates plants have completely recovered from slight herbicide drift and will not need replanting.

Purple corn - Many lower corn leaves commonly turn purple during the first couple weeks of May as a result of phosphorus deficiency. New leaves emerging from the whorl are usually green, but may turn purple shortly thereafter. Phosphorus deficiency symptoms often occur as young plants are exposed to good growing conditions following cool and often wet conditions. This results in a lag phase where vegetative growth exceeds the roots' ability to supply phosphorus. Young plants are especially vulnerable because their root systems are small and phosphorus is immobile in the soil solution. Any cultural or environmental factors that limit root growth will aggravate deficiency symptoms. Examples of such conditions include: cool temperatures, too wet or too dry soil, compacted soil, herbicide damage, insect damage, and root pruning by sidedressing knives or cultivators. Acidic soil can also intensify phosphorus deficiency symptoms. Low soil pH severely limits phosphorus availability to plants, which may cause deficiency symptoms, even where high soil test phosphorus levels exist. Plants normally recover when favorable growing conditions allow root expansion. Phosphorus deficiency, however, will likely reduce yield by delaying maturity, decreasing root and stalk development, and reducing energy transfer and storage. Treatment options to quickly remedy phosphorus deficiency have limited effectiveness, because phosphorus is immobile in the soil solution. Surface application of phosphorus fertilizer will be tied up in the top couple inches of soil. Phosphorus injected as a sidedress treatment would increase availability to roots, however, you need to be careful not to prune roots.

Replanting suggestions - Planting corn in May significantly reduces yield potential because development is delayed, which increases the chance of late-season water and heat stress and insect and disease pressures. Corn planted during the optimum time frame spaced uniformly at about one plant per foot of row will still have around 80 to 90 percent of optimum yield potential, depending on the yield level. Delaying planting into May would reduce yield potential similarly even with an optimum stand. Therefore, I normally only suggest replanting corn in May if the initial stand is a disaster and other crop options are not available or not economically feasible. When replanting corn, destroy the existing stand with herbicides or tillage before replanting. Surviving plants will have a huge disparity in plant development, causing severe competition with the adjacent replanted plants. This results in significant yield loss because of a high percentage of barren plants.

Grain Sorghum

Dr. Erick Larson

Sorghum establishment - Scout sorghum fields diligently during establishment for stand and insect pest problems. Sorghum seedlings have considerably less vigor than corn, which often translates to more a difficult stand establishment. Chinch bugs also prefer sorghum, as compared to corn. Because chinch bug populations tend to thrive during warm, dry conditions that are normal in May, they can cause major sorghum-establishment problems. Scout sorghum fields every 2 days until sorghum exceeds 6 inches, and then gradually decrease scouting frequency.

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