Agronomy Notes

November 5, 1999

Contents

SOIL AND NUTRIENT MANAGEMENT

Dr. Larry Oldham

Some "factoids" from the National Soil Survey Center. * Shrinking and swelling of some types of soil damage buildings, roads, and other structures. Repairing this damage annually costs the United States more than repairing the total damage from hurricanes, tornadoes, and floods. * The tips of small plant roots move through the soil with a twisting screw-like motion. Mature trees can have as many as 5 million active root tips. * A single spade full of rich garden soil contains more species of organisms than can be found above ground in the entire Amazon rain forest. * Although the soil surface appears solid, air moves freely in and out of it. The air in the upper 8 inches of a well-drained soil is completely renewed about every hour. * The plants growing in a 2-acre wheat field can have more than 30,000 miles of roots, greater than the circumference of the earth. * The "earthy" smell of newly plowed ground is believed to result from chemicals produced by micro-organisms. One of these chemicals, called geosmin, is produced by actinomycetes, organisms that have some properties of both bacteria and fungi. * About 10 percent of the world's land is used to grow plants and to feed animals or humans. About 20 percent of the land in the United States is used to grow crops. * Soil can act as a sink or a source of greenhouse gases. An estimated 30 percent of the carbon dioxide, 70 percent of the methane, and 90 percent of the nitrous oxide released to the atmosphere each year pass through the soil. * Worldwide, an estimated 25 percent of the soils used for agriculture are being degraded at an unacceptable rate. * The American Midwest has the largest area of prime farmland soils in the world. Other large areas are in South America and in Eastern Europe and Russia. * In the spring of 1934, a dust storm originating in the Great Plains carried an estimated 200 million tons of soil to the northeastern United States and out to sea. This storm caused "muddy rains" in New York and "black snows" in Vermont. * In 1950, there was more than half an acre of grain land for each person on Earth. By 1990, there was less than one-third of an acre per person. By 2030, there will be only one-fifth of an acre per person. * At field capacity, the amount of water available for plant growth ranges from less than 5 to as much as 50 percent, with an average of about 15 percent. * It takes about 4,000 to 6,000 pounds of crop residue per year to maintain the content of organic matter in a soil. * Modern farming practices that minimize soil disturbance (plowing) and return plant residues to the soil, such as no-till farming and crop rotations, are slowly rebuilding the Nation's stock of soil organic matter become tied up in the bodies of organisms and 60 to 75 percent is respired as carbon dioxide back to the atmosphere. Only 10 to 25 percent is converted to humus in the soil.

SOYBEANS

Dr. Alan Blaine

As you begin to make plans for the coming year, focus on the basics of crop production. Several new technologies are available but none are substitutes for good management. Expectations for the upcoming season will require you to zero in on what works and to provide a level of management that accounts for every input.

The Group IV variety trials (Roundup Ready and conventional) are currently available at your county Extension office. Hopefully, by the time you read this, the maturity groups V and VI variety trials will also be available. As you evaluate varieties, keep in mind that varietal differences are real. Base the majority of your choices on past and performance and consistency across locations.

Avoid getting caught up in selecting varieties because they are new. I am not discouraging you from trying new varieties, just reminding you to plant the bulk of your acreage in proven performers; don't experiment on a large scale. If a new variety is that promising, it will be around next year and furthermore, there will not be enough seed available the first year to meet everyone's needs.

The vast majority of the problems soybean growers have encountered over the last couple of years have been on relatively new varieties. Instead of taking 6 to 8 generations for a variety to reach the market, we are seeing varieties blown up and put on the market in probably 3 to 4 generations. It is this trend that has caused many of you to experience poor performance from many new varieties.

Steer away from planting a variety just because someone tells you how good it is. Prove it to yourself and this should be done with no less than 2 years of yield test data. Variations in growing conditions cause varietal differences to be expressed, and 1999 really exposed some potential weakness in several varieties.

It is imperative this coming season to focus on practices that have proven to be beneficial. Early planting and the use of early maturing varieties are two practices that will increase next year as a result of 1999. Although the hot, dry weather was a major factor some of the problems encountered, could have been avoided. One of the biggest problems we have statewide is the lack of in-field scouting. Plants remaining green or plants with erratic fruit set might have been minimized if the cause was identified when it occurred instead of after the fact.

Green plantsñIn a dry year ( such as 1999), you can map your soils based on plant appearance. Many growers expressed concern about plants remaining green but most plants that remained green did so because they had set very little fruit. A plant's sole purpose is to make a seed. Once we finally begin to get some moisture, these plants attempted to start the fruiting process all over again due to the lack of fruit. Usually the areas that greened up or remained green were the droughty areas of the field. It appears some varieties had more of a problem staying green, but to know for sure, you must first determine why they are staying green: is it because of the lack of fruit set, or is it due to the superior health of plants in the green areas? Many of you will not believe this, but most years soybeans dry down prematurely because of disease pressure. When plants with a good fruit load remain green, it is having a positive effect on yield; however, this year most was because of poor fruit set.

Charcoal root rotñCharcoal is present most years. It is mainly observed in dryland fields and much more pronounced in extremely dry years. Charcoal is a disease incited by some form of stress, which can result from being too dry or too wet; in other words, going from one extreme to another. It appears some varieties may vary in susceptibility to Charcoal, but no one to my knowledge has developed a rating for varieties, because of the erratic occurrence from year to year. Charcoal is probably the most devastating disease in the Midsouth. When it occurs, it is worse than stem canker and Phytophthora combined.

In an irrigated environment, if charcoal is observed, it tells me irrigation scheduling was inadequate. Many growers report they had plenty of rainfall this year, but at the same time, they are cutting below-average yields in irrigated fields. Is there a pH/fertility problem or other problems hurting yields other than water? At season end, it is hard to say, but we have found that many irrigated fields are not properly watered.

Water use from mid-July through pod fill ranged from 2.25 to 2.50 inches per week. One inch every 4 days would require a pivot to run continuously, and then it would still fall behind. Inadequate scheduling may be somewhat like teasing a crop with water, particularly in a year such as 1999. This gap in scheduling was probably enough to set off charcoal, maybe even make it worse than in a dryland field; since a dryland field may have allowed plants to slowly prepare for dry conditions.

Irrigation is a luxury for some, but it is a luxury that should be used more efficiently. Because charcoal is the result of a stress condition, anything you can do to avoid stress will help minimize charcoal. Crop rotation, proper fertility, deep tillage, early planting, early maturing varieties can all be beneficial. Hopefully, in the future we can help more in the area of varietal choices.

COVER CROPS COULD HELP

Dr. Malcolm L. Broome

Many advantages to using cover crops exist but few cover crops are grown by Mississippi farmers. The book Managing Cover Crops Profitably, published by the Sustainable Agriculture Network, lists cover crops as a way to slow erosion, improve soil, smother weeds, enhance nutrient and moisture availability, reduce costs, increase profits, and even create new sources of income. With all the benefits, why are cover crops not used?

The reasons most often mentioned for not using cover crops are the cost of establishment and management needed to plant the next crop. However, given the current economic situation for row crop farmers, cover crops might deserve more than a quick disregard. We know a legume such as clover or vetch can contribute nitrogen to crops grown after them, thus allowing nitrogen fertilizer to be reduced. Research shows 30 to 60 percent recovery of nitrogen fixed by these cover crops. This reason alone could justify the use of a cover crop. Protecting soil from erosion is another benefit that is added on by growing a cover crop. Soil lost to erosion is quite expensive and can never be recovered on that farm. Research in Mississippi using wheat, crimson clover, and hairy vetch reduced erosion allowed no-till planting of cotton and maintained excellent cotton yields. In a dry year, residue from cover crops will increase water infiltration and reduce evaporation.

In spite of all the benefits, cover crops do require some thought and planning in their uses. Things such as how to plant, weather at time of planting, how easy can the crop be killed and planted into, labor and equipment needed, and amount of extra time to make it work must be considered. If you think you could benefit from using a cover crop and would like more specific details or assistance in planning a cover crop program, contact your county Extension agent. Time is getting short to plant a cover crop for this year but planting could still be done successfully with proper planning.

CORN

Dr. Erick Larson

Crop RotationñRecord 1999 corn yields and a hopeful market should rejuvenate interest in corn production next year. However, crop rotation is the primary reason you should be planting corn on part of your acreage. The reason is simpleñcrop rotation significantly increases productivity of all your crops in the long run. Reports consistently indicate 10 to 20 percent yield advantages for cotton or soybeans grown in rotation with corn on Mississippi farms. Crop rotations normally improve yields because many weed, insect, nematode, and disease problems build up when using the same management program every year in continuous cropping. Crop rotation systems effectively disrupt many of these cumulative effects, preventing problems and reducing input costs. Crop rotation allows the producer to attack the predominant weed problems by altering tillage systems, changing herbicide chemistry, and disrupting weed life cycles. Corn rotations can also improve soil physical structure by recycling more organic matter and changing from a tap rooted crop to a fibrous root system. Numerous other beneficial effects of rotation have been reported, including improvements in soil fertility, soil moisture, soil microbes, and phytotoxic compounds and/or growth promoting substances originating from crop residues. Growers can maintain these benefits by continuing to rotate crops on a yearly basis. A crop-rotation system also spreads risk in case of unpredictable problems such as with the late-season drought (on cotton and soybeans) this year.

How long should I grow corn?ñThe rotational benefits described generally diminish every year after the first year in a rotation system. Additional yield, soil improvements, weed control, and nematode benefits are sometimes realized by a 2-year rotation, particularly if the field has been continuously cropped for a long time. However, yields will gradually decline and pest problems substantially arise the longer corn is grown continuously. This reduces potential gross return, while increasing potential risk and/or input costs. Thus, I do not suggest not growing corn in the same field for more than 2 years.

Fall corn borer controlñFall tillage can reduce survivability of overwintering corn borers considerably. Fall discing shreds stalk tissue and most importantly, may dislodge, tear up, and expose the crown area of the stalk. The crown is the primary overwintering area in the stalk for the southwestern corn borer. Thus, many operations that do not disturb this area, such as stalk shredding, subsoiling, and rowing up, will not affect overwintering survivability very much. Stalk shredding may be effective against European corn borers, because they overwinter higher up the stalk, but this species has not been quite as prevalent as the Southwestern corn borer in most of the state.

COTTON

Dr. Will McCarty

Variety Selection: Variety selection is one of the most important business decisions cotton growers make. The longstanding and ongoing position of the MSU Extension Service is to extend variety trial research results, coupled with direct professional experience, to allow crop producers to make their own informed variety selection decisions.

General guidelines for variety-related recommendations by MSU-ES scientists are these: 1) to recommend that crop producers combine MAFES variety trial information with on-farm personal experience to select varieties that will perform well on their farms. 2) to recommend that crop producers try new varieties only on a very limited acreage. 3) to recommend that crop producers plant the bulk of their commercial acreage in proven performers. 4) to recommend that crop producers critically evaluate the need for value added traits in transgenic varieties.

The weather had a tremendous effect on several varieties this season. This was evident by the amounts of bronze wilt and cavitation. I will go into these in more detail in the next edition. Hopefully I will have some variety trial information to share at that time as well.

Fall Jobs - Cut stalks as soon after harvest as is possible. This will help in boll weevil control efforts. Sandy soils should be subsoiled when compaction problems are shallow enough to shatter and soils are dry enough. Avoid tillage operations on wet soils. Leave subsoiled fields rough until spring.

Alternate Practices For Clayey Soils - Heavy-textured soils offer several options. Consider some form of reduced tillage or stable seedbed system. Heavy soils are excellent candidates for fall tillage. Fall hipping and planting on a stale row after a burn-down program in the spring is a good option. For heavy-textured soils, planting on a stale seedbed may mean the difference in planting on time in late April/early May, planting in June, or not planting at all. Controlled traffic, confining all traffic to a particular pattern, is a very good tillage alternative, can reduce tillage trips, improve soil tilth, and increase profits.

Monitor Soil Fertility Levels - Fall is an excellent time to test soil. Cotton is an intensely managed crop and requires high levels of fertility to produce acceptable yields. While cotton farmers generally practice good soil fertility programs, there is still a lag in soil fertility levels. A review of the 1995-96 reports from the Mississippi Cooperative Extension Service Soil Testing Laboratory shows, more than 25 percent of the samples submitted statewide for cotton tested below medium for potassium. This compares to 14 percent for soybean samples. Producers must pay closer attention to the fertility status of cotton soils, and not just potassium, but other nutrients as well. Especially monitor pH. If pH levels are low and soil test recommends lime, it is critical that it be applied. If pH levels are low, applied nutrients such as nitrogen, potassium, and especially phosphorous will suffer a reduction in efficiency.

Low Soil pH = Low Yields - Fall is the preferred time to apply lime and also is an acceptable time to apply mixed fertilizers to soils with a CEC of greater than 7. On soils with a CEC of less than 7, leaching of fall-applied fertilizer may be a concern.

Growing cotton in low pH soils can lead to root growth problems, nutrient deficiencies, and/or toxicities. Liming acid soils will improve plant growth and significantly increase the efficiency of applied fertilizer nutrients. In fact, if pH levels are in the low 5's or high 4's, applying fertilizer nutrients may be almost a waste of money. If lime is required, it should take precedence in a fertility program.

Selecting lime material is also important. When selecting lime materials, be sure they meet the requirements for Grade A as set by the state's lime law, which is for your protection and regulates the quality of material that can be sold as agricultural lime. Particle size and calcium carbonate equivalent (CCE) are the major considerations, and of these two, particle size is perhaps the most important. The larger the particle size, the slower the material will react and the poorer the quality of the material.

Be careful as you select materials. Pelletized lime and/or liquid lime materials can be good sources, but consider the CCE and quantity of application. If the recommendations call for l ton per acre of a 90-percent CCE material, applying 500 pounds per acre of a 95-percent CCE material will not meet the requirements. Be careful and always consider the CCE of the material you select.

Nematodes: Nematodes, especially Reniform, numbers have been going up each year. If you have not had your soil sampled for nematodes I would suggest the efforts be made. This is especially true if growth and yields have been erratic in fields or parts of fields. Use of nematicides and/or rotation with corn/grain sorghum have proven to provide significant yield increases in Reniform infested fields. However, infestations must be detected before cost effective control strategies can be implemented.

Upcoming Meetings:

Cotton Short Course - December 8 - 9, Mississippi State University Delta Agricultural Expo - January 25 - 26, Cleveland, MS Agri-Day - February 2, Greenwood Civic Center Southern Soybean Conference - February 7 - 8, Memphis, TN Certified Crop Adviser Training - February 14 - 17, Mississippi State University

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