Agronomy Notes

May, 2001

Contents

COTTON

Dr. Will McCarty

While weather has not been terrible, neither has it been perfect. Because of the rains and cool weather of late April, replanting may be necessary for some early planters. Planting cotton in early April is a risk, and only a few took the risk. For the most part it looks like the gamble may pay off this year. Too often, though, planting cotton in early April will result in a very high percentage replant.

According to the Mississippi Agricultural Statistics Service, as of April 29, 28 percent of Mississippi's cotton crop had been planted, compared to 17 percent on that date last year and 12 percent for the 5-year average. For those farmers who have not planted, you are not late! The first of May is really the ideal time to plant cotton. Year in and year out, cotton planted the first two weeks of May will catch and surpass cotton planted earlier, mature within a few days of earlier planted cotton, and often out yield earlier planted cotton. Too, it will generally produce fewer sleepless nights when frost is in the weather forecast.

Whether planting early or late, farmers frequently have to deal with the question of whether to replant part or all of their cotton. The decision is often difficult to make. In fields with questionable stands, you must consider several factors before making a replant decision.

  • What is the calendar date?
  • What is the population of plants that will survive?
  • What is the health of those plants, especially their roots?
  • Are there large skips and frequent skips?
  • What is the productive capability of the soil, and is the field irrigated?

Calendar date is significant; a stand you would plow up on May 1 would probably be kept on May 25. Use of Bt cotton for protection from late-season budworms and boll weevil eradication make this decision easier than in the past.

If plant distribution is fairly uniform in fields on productive soils, good yields can be made with plant populations in the low 20,000 range, or as low as one per row-foot with no or few skips. If the stand is broken with numerous skips, replanting is in order at populations below 30,000 plants per acre, depending on the size and frequency of skips. In some cases a grower may "spot-in" areas of the field with his planter.

A big consideration is soil type and moisture. If the soil type is one that dries quickly, replanting decisions must be made ASAP and carried out before moisture leaves the beds. Replanting on these soils (generally mixed texture to heavy soils) may require returning to replant these fields before first planting of other fields is complete. To delay is to risk rain recharging the beds or having the limited stand survive. If replanting is necessary, continue to use fungicides as appropriate; that decision needs to be made on a field-by-field basis. If your replant is on the stale row, use a burn-down herbicide to kill the old stand and any weeds that may have emerged on the row. In some cases the bed may need to be "freshened" before planting. Again, you will need to make this decision on a field by field basis.

Other replant tips:

  • Make the replant decision quickly and act quickly before moisture limits your options.
  • If you have enough cotton in the field to really make the decision difficult, keep it!

SOIL TESTING

Dr. Keith Crouse

Soil sample arrivals at the laboratory have slowed down, and the lab is currently caught up with samples submitted for analysis. The lab has averaged a 3- to 5-day turnaround on samples. Clients who submitted samples 7 to 10 days ago should call the lab at 662-325-3313 to verify whether their samples have been run.

SOYBEANS

Dr. Alan Blaine

Mississippi soybean farmers set a new record this spring, with official reports of 45 percent of the crop reported planted by April 21; unofficially, estimates are that close to 60 percent of the crop had been planted. Some acreage was planted as early as early March. The percentage of Group IV's planted is the highest ever--between 50 and 60 percent.

Several areas of the state missed an excellent opportunity to apply some burndown herbicides this spring. For growers who waited to till a field, or waited late on a burndown, the recent rains become a major factor influencing their plans.

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

Burndowns are a tool that should be used more widely and more early than they are. Calls concerning burndowns are usually not about small, easy to control vegetation but about large troublesome weeds such as dock, smartweed, ryegrass and primrose. Often, the calls come in after these weeds have gotten extremely large, when farmers are closer to planting, resulting in some planting restrictions on some excellent materials.

A burndown program is nothing more than a tradeoff for tillage. Will it save you money? That all depends on what you use and when you get it out. However, on most soybean acreage in Mississippi, a burndown program gives farmers better control over planting dates.

Live vegetation can hinder soybean production in two ways. First, in a dry spring, it can remove precious moisture from the seed zone. Second, under cool, wet conditions, it will keep fields cooler and wetter longer, not to mention possibly providing a home for some unwanted pests. Consider using burndown herbicides, at least on a limited acreage next year.

Three major concerns about planting have surfaced this year. One is the failure to use the proper seed treatment. Another is depth of planting, and the third is what to do about less than desired stands.

Seed treatments are nothing more than insurance. The use of a broad spectrum material is not needed every year, or in every situation. However, due to the uncertainty of problems, it is justified. Two major seed treatment problems have come up this year with early plantings. One problem involved the proper seed treatment not being used, and one problem involved pythium following big rains.

Rhizome problems (although not often observed) were seen primarily on sandy to mixed soils. Avoiding rhizome problems is not difficult. There are many premixes on the market, and the cost is minimal. Although these treatments are not needed in every situation, it is better to invest than to regret. Choose quality products that offer broad spectrum control.

Several fields have been affected by non-lethal doses of pythium. Farmers with stands affected by pythium may want to consider increasing their mixture to 1.5 to 2X of a pythium material. Deeper planting also contributed to poor emergence. When planting early, plant more shallow; this makes it easier to get a stand, especially when there are heavy rains like those seen this spring. Faster emergence can reduce the incidence of pythium.

Several farmers have expressed concern over lower than desired plant populations. Many factors can contribute to thin stands, but most thin stands this year have been due to planting too deep, seedling diseases, and crusting following the 3-6 inch rains.

Soybean plants have a tremendous capacity to compensate for thin stands. If a stand is within 50 percent of recommended plant populations, replanting would probably not be advisable if weed control is good and the remaining plants are healthy. Populations even less than this are adequate if irrigation is available. Recommended plant populations are 75,000 - 125,000 plants per acre (row planting), or 125,000-175,000 plants per acre (drilled).

One of the main criteria in deciding whether or not to replant is the health of emerged plants. Two management options that will aid greatly in keeping a thin stand are Roundup Ready soybeans and irrigation. A slower closing canopy is one of the down sides to thin stands and the Roundup option (due to its broad spectrum weed control capabilities) can help out immensely. In addition, irrigation can help a crop grow off much faster. Evaluate stands closely before pulling the plug and starting over. Even discounting the expense of replanting, there is no way to compensate for early planting.

RICE

Dr. Joe Street

Much of the early-planted rice has emerged and is doing well. Flushing will be required on some of the rice that did not emerge after the mid-April rains. Uneven emergence can reduce milling yield because of different ages of rice in the same field. Watch for chinch bugs on the young rice. Chinch bugs could be a problem for young rice especially in reduced tillage systems, depending upon the chinch bug population in the grass surrounding the rice field. The best treatment is to flush the field, although insecticides are effective. After flushing, watch the levees for chinch bug activity. Treatment may be necessary on the levees to prevent excessive damage.

Another insect that attacks young seedlings is the grape colaspis or lespedeza worm. The larvae feed underground on the roots or the mesocotyl (stem) below the soil surface. They often girdle the mesocotyl, which results in yellowed and wilted plants. These symptoms resemble seedling disease but will generally be in short sections of a row rather than in circles in the field. Flushing the field is the only option to reduce the larvae population, and preventing water stress may allow some of the injured plants to survive. If you have the problem this year, consider using Icon-treated seed next year; Icon provides effective control to the grape colaspis.

The use of Ammonium thiosulfate as a carrier for Command is a popular practice to reduce the potential for drift and to add a little starter fertilizer. Be sure, though, that you recalibrate the spray rig for the liquid fertilizer, rather than using the same settings that were used for water. Otherwise the Command rate will be lower than planned and weed control will not last as long as desired. If you did not get the Command applied prior to rice emergence, it is now legal to tank-mix Command with postemergence herbicides as an early post treatment. Command has no postemergence activity and is safe on emerged rice.

Last year, there was a problem with controlling volunteer Roundup Ready soybeans in rice. Straight propanil did not kill soybeans more than six inches tall. These soybeans had emerged early and were tougher than the young beans normally found in neighboring fields. If you have this situation, add one-half pint of Grandstand to the mix to take care of the soybean after the rice is in the two-leaf stage or greater.

Some growers still have questions on fertility requirements for the new varieties. With Cocodrie and Priscilla, apply two-thirds to three-fourths of the total fertilizer preflood and the remaining fertilizer at midseason. With Wells, research has not shown any benefit to applying more nitrogen before flooding; therefore, we are currently recommending applying half at preflood and half at midseason. This will reduce the potential for lodging. The current recommendation is 150 to 180 pounds of nitrogen for each of these varieties. Apply the lower rate on new rice land and the higher rate on land that has been in rice before. If it takes more than five days to flood the field or in high pH (>7.5) fields, apply the higher rates to allow for losses due to volatilization. Both Cocodrie and Priscilla are susceptible to smut, so avoid excessive nitrogen, especially late in the season. Research data show that recommended Nitrogen rates usually yield as well as higher nitrogen rates, assuming that a timely flood is established.

Many growers do not like polypipe, but side inlet or multiple inlet irrigation can reduce pumping costs by up to one-third and save labor. Also, it allows more efficient utilization of fertilizer because of quicker flooding. This system may not work on every farm; try it first on a small acreage. Preliminary research shows that yields were reduced 80 to 100 pounds per acre per day of delay in flooding after nitrogen fertilization. If you cannot flood within five days, consider splitting the field if possible and making the fertilizer application so that water can be added accordingly. Again, side inlet irrigation will allow faster flooding and more efficient utilization of fertilizer.

FORAGES AND PASTURES

Dr. Malcolm Broome

Consideration for Pasture Renovation -

Pasture renovation simply means to "restore" or "make new again" a permanent pasture by changing management practices. It can be undertaken by changing one practice or by making several restorative practices. The reasons for the pasture's decline will determine the amount of renovation to be undertaken.

The following conditions (all of which could have been made worse by the 2000 drought) could be reasons for decline in a pasture:

  • Reduced production
  • Thin stands with bare ground exposed.
  • Poor drainage
  • Compacted soil on sloping areas.

If you decide to undertake pasture renovation, there are three basic practices that must be considered before moving to more aggressive practices such as disking or chiseling, sod-seeding, or replanting. These three practices are soil testing, fertilization and weed control.

Soil testing is the first step, and will lead to fertilization according to the reported analysis of your soil. In many cases, potassium has been depleted, due to either applying only nitrogen fertilizer for the past 2-3 years and/or removal of hay from the pasture. A 4-ton hay yield removes not only 200 pounds of nitrogen but 40 pounds of phosphorus (P) and a huge 160 pounds of potassium (K) as well. If you use a pasture for hay, apply 30-40 pounds of K for each ton of hay you remove. Low levels of K in the soil profile will result in reduced vigor, thus reducing the stand.

Weeds compete with grasses for water, sunlight and nutrients. Weeds can very quickly prevent establishment of young grass seedlings. If fertility is low and drought occurs, weeds will have an advantage over the grass, so some type of weed control must be used to help the grass compete. A number of research studies show 3-7 pounds of grass will be produced for each pound of weeds controlled.

Forages are the foundation of a successful livestock program. A successful forage program will require management that is focused on maintaining quality forage for animals to graze, and harvesting the excess as hay or silage in a timely manner. After the drought of 2000, our forage management will need to be first class to help restore Mississippi's pastures. If you need assistance with your forage program, contact your local county agent.

CORN

Dr. Erick Larson

Replanting/Late Planting suggestions - Late planted corn significantly reduces yield potential because plant development is delayed, which increases the chance of late-season water and heat stress, and insect and disease pressure. Corn planted during the optimum time frame spaced uniformly at about one plant per foot of row will still have around 80-90% of optimum yield potential depending on the yield level. Late planting can reduce yield potential similarly or substantially more with an optimum stand. Thus, planting corn in May is generally only recommended if the initial stand is a disaster and other crop options are not available or not economically feasible. The northeast region of Mississippi (north of Tupelo) can plant corn the first ten days of May without normally experiencing as much drought stress risk as the balance of Mississippi.

Kill an unacceptable stand - 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.

Purple/Stunted corn - Corn often appears stunted and lower corn leaves turn purple during the first couple weeks of May as a result of phosphorus deficiency. This deficiency is especially prevalent when corn is grown following a rice crop. 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 which limit root growth will aggravate deficiency symptoms. Examples of such conditions include: cool temperatures, too wet or dry soil, compacted soil, herbicide damage, insect damage, and root pruning by side-dressing 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. However, phosphorus deficiency 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, since phosphorus is immobile in the soil solution. Surface application of phosphorus fertilizer will limit availability to the top couple inches of soil. Phosphorus injected as a side-dress treatment would increase availability to roots, however, be careful not to prune roots.

Irrigation Initiation - Drought stress can potentially reduce corn yield anytime during corn's developmental stages. Therefore, irrigation should commence whenever soil moisture becomes limiting. Since corn's water requirement increases with plant size during vegetative stages (from emergence until tassel), plant growth stage does play a determining role, but there is not a definitive growth stage when irrigation should commence. This time is normally highly dependent upon seasonal rainfall. Corn's most critical and largest moisture requirement time interval is from tasseling through milk stages.

GRAIN SORGHUM

Dr. Erick Larson

Sorghum establishment - Scout sorghum fields diligently during establishment for stand, insect and weed problems. Sorghum seedlings have considerably less vigor than corn which often translates to more difficult stand establishment. Chinch bugs also prefer sorghum compared to corn and since chinch bug populations tend to thrive during warm, dry conditions which are normal in May, they can cause major sorghum establishment problems. Postemergence herbicide options for sorghum are quite limited, so timely identification and response also is imperative to control weed problems. Scout sorghum fields every two days until sorghum exceeds six inches tall and then gradually decrease scouting frequency.

Minimum Stand - Grain sorghum has tremendous ability to compensate for low stands by producing tillers, especially if plants are spaced uniformly. Thus, the optimum plant population for sorghum is very broad, ranging from 40,000 to 70,000 plants per acre for dryland production. Replanting would be required only if stands were reduced to less than two plants per foot of row or skips larger than five feet occur in adjacent rows.

SOIL AND NUTRIENT MANAGEMENT

Dr. Larry Oldham

Successful nutrient management involves knowing what you are applying to the soil, and how much. A common question is how to calculate the nutrient content of poultry litter or other byproducts used in a fertility program.

The following is an example that is being printed in several locations, and is available on the Fertilizer Management section of http:MSUcares.com/crops. It is worked up for poultry litter, but the basic math can be used for other materials.

Laboratory poultry litter analysis results:
moisture content = 25% (therefore dry matter = 75%)
nitrogen content = 4%
phosphate content = 2%
potash content = 3%

Calculations:
2000 pounds litter per ton times 0.75 dry matter = 1500 pounds dry matter per ton
1500 pounds dry matter per ton times 0.04 nitrogen content = 60 pounds nitrogen per ton
1500 pounds dry matter per ton times 0.02 phosphate content = 30 pounds phosphate per ton
1500 pounds dry matter per ton times 0.03 potash content = 45 pounds potash per ton

Results:
In this case, each ton of litter contains 500 pounds of water, 1500 pounds of dry matter, 60 pounds of nitrogen, 30 pounds of phosphate, and 45 pounds of potash.

Use:
Applying 2 tons of this product per acre will add 120 pounds of total nitrogen, 60 pounds of phosphate fertilizer equivalent, and 90 pounds of potash fertilizer equivalent.

Interpretation:
Organic byproducts are slow release fertilizers. A rule of thumb for nitrogen availability is that half of the total applied will be available during the course of the growing season when applied. About 12% will be available during the second season, and 6% the third. The scale of availability continues downward over subsequent years.

Much of the phosphate will be bound by soil particles, so it is difficult to predict availability without knowing more site specific soils information. Published data ranges from 10% to 70% availability in the first year following byproduct application.

Potassium is largely a counter positive charge to large negatively charged anions in organic products. It will participate in a cation exchange reaction like inorganic source potassium when applied to soil. The net result is that most potassium will be used by growing plants during the first season after application.

 

 

Department of Plant and Soil Sciences
Box 9555
Mississippi State, MS 39762

Will McCarty, Ph.D.
Extension Leader

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