Agronomy Notes

March, 2001

Contents

 

CORN

Dr. Erick Larson

Plant density - Growers should strive for 18,000 to 30,000 plants/acre depending mainly upon a field=s yield potential, planter row width, and planting date. If a corn yield goal of 150 bu./a. (45 bu./a. soybeans or 2 bales cotton) is realistic, particularly under irrigation, then strive for 26,000-30,000 plants/acre. If this goal is unrealistic, then lower the seeding rate accordingly. Row width changes optimum plant population because it affects plant spacing. Spacing seeds closer than six inches apart increases competition for light, water and nutrients, and weakens stalk quality without increasing yield potential, particularly under stress. Therefore, optimum plant population in wide rows is generally around 2,000 - 4,000 plants/acre less than narrow rows. Remember to over-plant desired plant population about 5 to 10 percent, depending upon seed germination and planting conditions. Early planted corn (soil temperature 50-55 degrees F) should be seeded slightly thicker than normal because cool spring conditions cause higher seedling mortality and shorter plants at tassel, meaning more plants are needed to intercept light. Conversely, growers should lower seeding rate with later planting dates since warm soils enhance seedling establishment, taller plants are produced and yield potential decreases.

Plant uniformity - Poor plant spacing and seeding depth is a common problem that may affect yield potential as much as plant population does. Research indicates that most growers could improve yields 5-15 bu./a., simply by improving planter performance. Best of all, this improvement will not cost you a dime. One common cause of seed distribution problems is excessive planter speed. The optimum speed for plate-type planters is 4.0-4.5 mph and 4.5-5 mph for vacuum-type planters. Higher speeds will usually cause much poorer seed spacing and less seed depth uniformity because seeds are rolling and bouncing in the seed furrow. Corn plants are extremely sensitive to plant spacing because they do not tiller or produce branches to alter their plant size. Crowded or late-emerging plants produce small ears and spindly stalks due to excessive competition for light, water and nutrients. Corn seed is available in numerous combinations of size and shape; this may further aggravate planting problems. Growers with plate-type planters should match planter plates with their seed size. Likewise, growers with vacuum-type planters should match disc size with seed size and match air pressure with their seed. Also, excessive wear to planter plates or finger pick-ups often causes major problems; just because something worked last year doesn=t necessarily mean it will work this year.

Planting depth - Many producers unfamiliar with corn seedling development plant corn too shallow. Corn seed should be planted 1 2 - 2 inches deep. Planter depth should be set in the field during planting. This is important because soil type, seedbed condition and moisture may influence actual depth. Corn seed=s inherent energy and germination process ensure emergence from depths as great as 3 inches. The origination point of the nodal root system is moved upward when corn seed is not planted deep enough. Corn seed placed less than 1 inch deep will develop nodal roots at or above the soil surface. This exposes these roots to factors such as hot, dry soil, herbicide injury, and insect predation which can significantly hinder root development. This often leads to standability problems, nutrient deficiencies and even drought stress throughout the year. Birds may also cause stand loss by extracting shallow planted corn seeds.

Bt Refuge - Growers can plant no more than 50% of their corn acreage in Bt hybrids trademarked YieldGard which contain the MON-810 insertion event. Growers will be required to sign an agreement requiring them to plant non-Bt corn as a refuge within a half mile of the Bt corn. Neighbors= conventional corn does not count as refuge. The non-Bt refuge may be treated with insecticides (excluding sprayable Bt products) as needed. These refuge requirements for YieldGard Bt corn in Mississippi are the same as last year.

Should I plant Bt corn? - Bt corn effectively controls both Southwestern and European corn borers and has moderate control on corn earworms and fall armyworms. However, Bt corn does not control the primary insect pests during stand establishment, such as chinch bugs, cutworms, rootworms, wireworms, etc., so using a Bt hybrid will not eliminate the need for a soil-applied insecticide at planting. Preliminary research data and industry yield trials suggest the inclusion of a Bt event does not increase hybrid yield potential compared to a closely-related conventional isoline in the absence of corn borers. Therefore, a grower would not likely recover the higher seed cost of the Bt technology (about $10 per acre) unless significant corn borer infestation is likely. Unfortunately, seasonal corn borer populations are not very predictable; local historical infestation levels should be used to justify Bt hybrid use.

WEED CONTROL

Dr. John Byrd

EPA has approved our request for Oasis (imazapic + 2,4-D ester) for postemergence control of vaseygrass in bermudagrass pastures and hayfields. The application rate is 4 to 6 fluid oz/A plus NIS when vaseygrass is 2 to 8 inches tall. A maximum of 20,000 acres may be treated. There is a 7 day grazing restriction for dairy animals, a 30 day haying restriction, and meat animals must be removed from treated pastures or hay 3 days before slaughter.

There is also a 60 feet buffer restriction between sites of application and the two endangered plants, pondberry (known population are found in Bolivar, Sharkey, and Sunflower counties) and Price's potato-bean (known populations found in Clay, Lee, and Oktibbeha counties). Oasis users in these counties should contact the U. S. Fish and Wildlife Service or Mississippi Department of Agriculture and Commerce to determine if these endangered plants exist near targeted application sites.

Imazapic, the active ingredient in Oasis also has activity on a number of other grassy weeds, including both Argentine and Pensacola bahiagrass, crabgrass, foxtail, little barley, ryegrass, sandbur, and many broadleaf weeds, including perennial sedges. We will be evaluating the effectiveness of Oasis on many of these grasses and bulrush this summer. Producers should be aware that last summer, Oasis significantly reduced bermudagrass yield at rates as low as 8 oz/A. However, it was difficult to differentiate how much of this yield loss was due to lack of rain. Although yield was reduced, there was an increase in bermudagrass quality.

PASTURE AND FORAGES

Dr. Malcolm Broome

Quality forage for beef cattle is becoming more important as stocking rates increase and the cost of production inputs (such as land, fertilizer, and seed) continue to rise. Quality forage is forage that contains a high percentage of total digestible nutrients (TDN) and is readily consumed. It must have a high percentage of protein, low percentage of fiber, high leaf-to-stem ratio, and high energy potential. All producers and purchasers of forages should recognize the value of quality grasses, legumes, and hay. It does not cost much more to produce quality grazing and hay than it does to produce fair or poor quality hay.

Many factors affect the quality of a forage, but there are four that you can control: the stage of growth when plant is grazed or harvested; the time of year the forage is grown; the fertility content of the soil; and the nature of the plant species.

Stage of growth - All forage plants are higher in quality when young than when mature. Grass leaves mature from the tip downward. Also, the cell walls are thinner when young, making plants more highly digestible. Young plants usually contain more nitrogen, resulting in an increased protein content. Even though the yield is usually greater when the plant approaches maturity, much of the quality has been lost. Some sacrifice in total yield will result in higher quality forage, which gives more beef or milk production per acre of forage. To get maximum energy and protein per acre, you should graze grass before seed head formation, or harvest for hay in the boot stage.

Time of year - Summer grasses lose quality as the season progresses, even though you may harvest the forage in the proper growth stage. This loss of quality in late summer is caused by shorter days, higher temperatures, and lower available soil moisture content. Therefore, the first hay clipping or first few weeks of early summer grazing are higher in quality than the rest of the season.

Fertility content of the soil - The amount of available plant food, especially nitrogen, determines the yield and (to some extent) the quality of a forage. The amount of nitrogen in the plant tissue determines the protein content. Research has shown that nitrogen fertilization also increases the animal preference for the forage, the amount consumed, and to some extent, the digestibility.

Nature of the plant species - Grasses are normally lower in quality than legumes, and within each group there is a wide range of quality. Grasses also vary in quality. Normally, cool-season grasses are higher in quality than warm-season grasses, and annuals have higher quality than perennials.

Management can play a big part in providing quality forage and getting the most out of each production input. With today=s production cost, quality grazing and hay are expensive enough already. Good management techniques help producers get the highest return for their investment.

NUTRIENT AND SOIL MANAGEMENT

Dr. Larry Oldham

Fertilizer prices are still a prime topic. The following press release from the Fertilizer Institute was compiled from a survey of fertilizer producers in January 2001.

According to the Fertilizer Record, production of anhydrous ammonia in January 2001 was 48 percent lower than production in January 2000. For the period covering July 2000-January 2001, production of ammonia was 20 percent lower than the same period in the previous year. Urea production was down 45 percent in January compared to the same month last year, and down 21 percent in the July-January comparison.

Inventories of nitrogen were down 18 percent in January compared to January 2000. For specific products, nitrogen solutions inventory was down 48 percent and urea was down 27 percent.

Nitrogen producers and distributors are working to meet farmer demand for nitrogen this spring planting season. Beginning in mid-January, moderation in the price of natural gas, combined with higher prices for nitrogen products, enabled producers to resume production at several idled plants.

Significant increases in nitrogen imports will lead to a record level of imports this year. Weather and distribution issues will play a role in determining the availability of specific nitrogen products being present in the place and time needed by farmers.

On January 26, nitrogen prices in Mississippi were still about 110% greater than one year ago. Due to the manufacturing increase, supply seems to be less of an issue than one month ago. See last month's Nutrient Management Agronomy Notes on managing nitrogen for optimum efficiency.

For phosphate and potash fertilizers, pay close attention to soil tests. Hopefully you have already enacted an effective liming program that allows you to maximize use of P and K already in your soil.

Soils testing high or very high for P and K on a current soil test do not routinely need additional fertilizer. Any recommendation is to meet maintenance requirements for the nutrients removed by the harvested crop. Soils testing in the higher part of the medium category may not respond to fertilization. Soils testing in the lower medium part of medium, low, or very low probably should be fertilized for optimum production.

SOYBEANS

Dr. Alan Blaine

Planting time is rapidly approaching and recent rains have delayed plans in some areas. December broke a record as the second coldest December ever. This extended cold period aided in the suppression of insects and slowed the growth of many winter weeds. Recent warm temperatures will promote early growth of most winter vegetation; do not overlook checking fields in order to apply timely burndown. It is time now to apply a burndown or to give serious consideration to when to apply a burndown.

Just because you utilize burndown herbicides, this does not mean you are restricted to no-till. Reducing tillage is an individual decision that may vary from year to year, but it is an option that will work and will reduce costs. For no-till or reduced tillage to work, farmers have to concentrate on fall tillage rather than relying on uncertain spring weather. Waiting on a spring tillage window to open up is 50/50 at best. Applying burndowns early will let fields dry and warm faster. Do not wait too long; early burndowns are the most cost effective.

After our excellent fall weather, farmers need to consider minimizing tillage to take full advantage of a burndown option. Even if you feel some form of tillage is a must, a low rate of an effective burndown material will help minimize the amount of tillage needed. Apply burndown options soon. Adjust your rate to cover weed size and weed species present. Do not let this vegetation get a head start. While it is too wet/cool to begin planting, let burndown materials be working; their activity is slower under cool conditions.

Many fields in the Delta will fall under the burndown restriction imposed from March 14-May 1. Provisions are in place for exceptions, as mentioned elsewhere in this edition of Agronomy Notes.

The cold weather in December, the super saturated soil and overcast conditions, and intermittent cool weather (decreasing the last few weeks) has delayed early season growth. Under sunny conditions, though, this vegetation will get ahead of us very fast.

Several excellent options are available. Clarity, 2,4-D or mixed with Roundup, Touchdown, or other glyphosate formulations make an excellent broad spectrum mix. Goal mixed with the same materials could provide some residual at the correct rates. Make your choice based on what is in the field.

The need for a residual material should be determined based on time of year, weed species present and whether you will grow Roundup Ready soybeans. Conventional beans could use more help than Roundup Ready beans, since Roundup Ready growers will have another opportunity for weed control with the first pos-emergence treatment of Roundup

COTTON

Dr. Will McCarty

Stale Seedbeds: It is not a good idea to let natural vegetation grow excessively large before applying burndown herbicide. This is especially true on heavy textured soils. There are several reasons for this but two easily come to mind:

  • Smaller vegetation is easier to cover and control with burndown material.
  • Plants are perhaps the most efficient moisture pumps in existence. Growing vegetation can dry seedbeds very quickly. If vegetation is allowed to dry seedbeds, additional rain will be required before planting. This is especially true for narrow rows. A narrow row bed (30 -32 inches) contains less soil volume than a 38-40 inch row. The key is to let the vegetation get large enough to provide some soil cover but not large enough to be hard to control.

Planting Date: Determining when to plant is one of those situations where a little knowledge must be tempered with a lot of common sense. A general recommendation for planting date is to plant when soil temperature at the two-inch depth is 68 degrees F and the five- to seven-day forecast calls for an accumulation of 50 to 60 DD60s. This occurs earlier some years than others.

Common sense must apply but the long-term average indicates that the last two weeks of April and the first two weeks of May are usually the most favorable for planting. Never set a calender date and start planting. Use soil temperature, soil moisture saturation and weather conditions as a guide. The first 24 to 36 hours a seed is in the soil is the most critical. If a cotton seed imbibes cold water (in the low 50'sF) root damage may occur and emergence will be significantly reduced. An emerged cotton seedling has a better chance of surviving a spell of adverse weather (cool front with an associated shower) than does a sprouting seed. Remember: common sense must apply; look at the soil and weather and do not be handcuffed to a particular calendar date.

Seeding Rates: Monitor seeding rates closely. The tendency may be to plant a little thicker to be sure a stand is achieved. This could backfire. If a transgenic variety is being planted, seeding cost could be excessive. Too, cotton planted too thick will tend to fruit a little higher and the weaker seed in the lot (later emerging) will be shaded; competition will render most of them unproductive. Consider soil conditions and seed quality and plant for a final stand of 3.0 to 4.0 plants per foot of row in 38 to 40 inch rows and 2.0 to 3.0 plants per row foot in narrow rows (30 to 32 inches). This usually translates to dropping about 4 to 5 seed per foot of row in 38 to 40 inch rows and about 3 to 4 seed per row foot in a 30 inch row.

Proper calibration of planters is very important. Optimum yields and crop development will generally occur at a plant population between 40,000 and 50,000 uniformly spaced plants per acre for almost any row spacing (with the exception of ultra-narrow rows where populations over 100,000 are needed). The more productive the soil, the lower the plant population that can be tolerated, as long as spacing is uniform.

Some tips for setting a planter are:

1. Use manufacture suggested settings only as a guide.

2. After settings are made by the use guide, run the planter on a hard surface such as a turn row. Measure 20 feet and count the number of seeds and divide by 20. Check several of the units, not just one. Make any necessary changes for the planter to deliver the desired number of seed per row foot. Forget about pounds of seed per acre, concentrate on number of seed per linear foot of row.

3. Forget about running the planter in the field and digging up seed for the purpose of setting plant population. You will never find all of them and the cotton will be too thick. Use the digging method only to set planting depth.

Use the table below to convert plants per row foot to plant population per acre.

To determine seeding rates you will need to adjust this number by an emergence factor. For example, if you are planting in a 40-inch row and want a final stand of about 45,000 plants per acre, according to the table you will need an average of about 3.5 living plants per row foot. Adjust this number by actual germination and what you expect to get up. If that number is, for example 85%, you would divide 3.5 by 0.85, which would equal 4.1 seed per foot. In other words, for that lot of seed, drop an average of 4.1 seeds per row foot for a final stand of 3.5 plants per foot.

Cotton specialists in Alabama and Tennessee make roughly the same recommendations.

RICE

Dr. Joe Street

Rather than the normal production information, this month=s space will be used to address an issue of increasing importance to rice growers, especially in areas adjacent to herbicide-tolerant cotton and soybeans. Drift of crop protection chemicals has been an issue since their initial use. We have had regulations concerning the use of 2,4-D; the restrictions placed on the use of burndown herbicides during March and April in Mississippi has brought increased awareness of the drift potential of these herbicides. New regulations from the Mississippi Department of Agriculture and Commerce prohibit aerial application of glyphosate, sulfosate, and paraquat between March 14 and May 1 except in emergency conditions. This was done primarily to protect young corn, but it has stimulated questions concerning drift onto rice. Concern is increasing because of the increased planting of herbicide-tolerant crops in the rice-growing region

Rice is most sensitive to glyphosate in the seedling stage and the reproductive (booting) stage of development. Drift symptoms are generally easy to detect in the seedling stage; however, drift at midseason or later may not produce readily visible symptoms. If rice seedlings survive the initial drift without excessive stand loss, they generally recover without significant yield reductions although maturity may be delayed. Drift during the booting stage will generally result in short flag leaves and distorted heads with parrot beaked grains similar to straighthead, but these symptoms are not always manifested. In many cases, the first symptom may be noticed at harvest in the form of reduced yields or reduced milling yields. In this case it is difficult to determine the cause of the problem or where it originated. All producers must use common sense when applying glyphosate-type compounds. Be aware of what is being applied in adjacent fields and document as much as possible. Glyphosate drift is a serious concern; with a common sense approach, farmers can minimize its impact on rice. Tremendous advances have been made in equipment to reduce spay drift; if farmers do not use it properly, the problem will continue to get worse and additional restrictions will likely follow.

As an update on the Section 18 status, the Mississippi Department of Agriculture and Commerce has applied for Section 18 exemptions for Regiment, RiceStar and Newpath. The Environmental Protection Agency (EPA) granted the RiceStar Section 18 for Arkansas and Louisiana and is expected to make it available for Mississippi for this growing season. Mississippi researchers did not apply for RiceStar initially because EPA projected a March registration date; however, it appears that they will not make that date for a full section 3 registration. RiceStar is Whip 360 with a safener added; it will control weeds essentially the same as Whip when applied according to label recommendations. When stretching the label, RiceStar is not quite as active as Whip. Crop safety has not been an issue with RiceStar. Regiment will control barnyardgrass and has good activity on hemp sesbania and northern joint vetch. Newpath will be used in the Clearfield rice system. Newpath has excellent activity on grasses, including red rice. Although it is not certain whether it will be a Section 18, an EUP or a 24C registration, some type label is expected by use season. Mississippi will have limited acreage of Clearfield rice (CL121 or CL141) available because of limited seed availability. For those fortunate enough to get some Clearfield rice, CL 121 appears to be better suited to Mississippi conditions because of its straw strength.

Several producers have raised questions concerning zinc seed treatment. Based on the limited research that has been done, growers could expect a response to zinc seed treatment if they are planting into a high pH soil (greater than 7.5) or the soil is a light silt loam or newly land formed. On the heavy clay soils with a pH less than 7.5, no significant response to zinc has been noted

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