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10/6/2008 - 10/12/2008

New Manure Nutrient Management Research Available

By John Sawyer, Department of Agronomy
Iowa crop and livestock farmers, as top producers of corn, soybeans, pork, eggs, and other agricultural products – are in an advantageous position economically and environmentally. Not only do livestock producers enjoy the benefits of locally grown crops for the feed that they need, but crop producers also enjoy the benefits of using manure as a nutrient source. To help producers make the most of Iowa’s available manure nutrient resources, Iowa State University Extension recently developed an updated publication, Using Manure Nutrients for Crop Production - PMR 1003.

“The publication will help producers manage manure applications for best use as a nutrient resource and therefore help reduce fertilizer requirements. This can help provide for good crop production and minimize environmental influences,” said John Sawyer, Extension soil fertility and nutrient management specialist and publication co-author. “The publication incorporates new research findings, including updates for estimating manure nutrient crop availability. This includes first-year availability, and when appropriate, subsequent crop-year availability.” Also, the publication has examples for determining the rates need to meet crop fertilization requirements from manure sources.
 
The publication has in-depth discussion on managing manure nutrients for crop production - especially manure nutrient characteristics, similarity/differences to fertilizer nutrients, manure nutrient processing in soils, and management practices that can affect nutrient supply and success as a nutrient resource for growing crops. This information will be of interest to both crop and livestock producers, as well as agency personnel and crop advisers.

The revised publication can be purchased or downloaded from the ISU Extension online store.

 

 


John Sawyer is a professor of agronomy with research and extension responsibilities in soil fertility and nutrient management.

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Fall Tillage Considerations for Soybean Disease Management

By XB Yang, Department of Plant Pathology
Fall tillage operations become a consideration at harvest time, and plentiful soil moisture makes moisture conservation a non-issue. However, the management of soybean diseases could be a consideration if you have fields with severe disease problems this year.

Tillage is an effective way to manage many crop diseases because it reduces the pathogen infested crop residue, and adjusts soil temperature and moisture. Several of the soybean diseases prevalent in areas of Iowa this year can be effectively controlled with tillage practices, and some cannot.

Diseases that can be controlled with tillage
Tillage practices are very effective in reducing the risk of almost all of Iowa’s soybean foliar and stem diseases – such as Cercospora leaf spot, brown spot, frogeye leaf spot, downy mildew, bacterial blight, brown stem rot, and Phomopsis. Pathogens of these diseases survive in crop residues in the absence of soybean crop. When infested crop residues are buried in soil, their decomposition rate increases and the fungi die. Tillage reduces the amount of pathogens that survive to the next crop.

Corn-soybean rotation helps reduce disease risk. The infested crop residues, especially infected leaves, will decompose during the next growing season even when left on the soil surface without tillage. In a soybean-corn rotation the infected soybean leaves may be totally disintegrated when corn is grown. However, there may be residue of infected soybean stems carried into the next soybean season. 

Diseases that are affected by tillage
Occurrence of white mold, SDS, and Phythophthora rot are greatly affected by tillage practice; the first two of these are prevalent in some areas of Iowa this season. Tillage has varying effectiveness on each of these diseases. For white mold control, use of no-till while growing corn immediately after a bad soybean while mold season is effective to reduce the disease. When left on the surface, white mold sclerotia, a survival structure, will germinate during a corn season (except seed corn).  Germinated sclerotia die and post no threat to soybeans.

Soybean sudden death syndrome becomes more severe under no-till than other tillage practices. Tillage increases soil temperatures and reduces spring soil moisture which helps cut the risk of soybean sudden death. Tillage to improve soil water conditions should be considered if Phytophthora rot – which occurs in saturated soil - is a severe problem.

Diseases that cannot be controlled with tillage
Soybean cyst nematode and some soilborne diseases, such as Rhizoctonia root rot, would not be reduced by tillage practices. In fact, tillage practices increase the movement of soybean cyst nematode and spread the risk.

                      soybean SDS

                 Soybean plants with sudden death syndrome.

 

 

XB Yang is a professor of plant pathology with responsibilities in soybean disease extension and research.

Fall Frost Effects of Forage

By Stephen K. Barnhart, Department of Agronomy
The first frost of the autumn generally brings a flurry of forage related questions centered around three general topics:

  • toxic prussic acid potential and management of frosted sudangrass and sorghum sudangrass hybrids;
  • is frosted alfalfa toxic to grazing animals; and
  • now that we've had frost, should I harvest the last alfalfa cutting?

 

Managing frosted sorghum sudangrass and sudangrass
The potential for prussic acid poisoning and management suggestions are related both to the size of the plant when frosted and the extent of frost damage. Producers should be aware that the risk of damaging levels of prussic acid is very unlikely.

Prussic acid, more correctly called hydrocyannic acid (a cyanide based compound) is formed in sudangrass or sorghum sudangrass hybrids which are severely stressed or frost damaged. The hydrocyannic acid develops within a few hours after the frost and usually dissipates within a few days. The safest management is to remove cattle and sheep from frosted fields for several days. Livestock can be returned to frost injured sudangrass that is 18" or taller and sorghum sudangrass 30" or taller after about 3 or 4 days. If the grass was shorter than these heights when frost injured, withhold cattle and sheep for 10 days to 2 weeks following the frost to avoid problems. Then watch for new shoot regrowth, (tillers or “suckers”) on partially frost killed plants! Direct grazing of these fresh new shoots can be toxic too. Where new shoots appear following frost, avoid grazing until 2 weeks after the "killing" frost that kills the new shoots.

Prussic acid poisoning is not a common occurrence. Very few verified cases are reported by veterinarians. Maybe Iowa producers are just using good management. Consider the recommendations above to be at the low risk or conservative level.

If in doubt, move the livestock to another type of forage. Livestock can be returned to the sudangrass or sorghum sudangrass fields following a "killing" frost and appropriate post frost delay period.

Frost damaged sudangrass or sorghum sudangrass hybrids can be cut and stored as silage. Hydrocyannic acid is dissipated during wilting and partially during the ensiling process. Observe proper ensiling technique, particularly moisture content, when ensiling these crops.

Sudangrass and sorghum-sudangrass hybrids are difficult to dry thoroughly enough for safe storage as dry hay. As with wilting and ensiling, most if not all of the hydrocyannic acid is dissipated in the drying process.

Producers who want to get frosted sudangrass or sorghums tested for hydrocyannic acid content should first contact a local forage or plant tissue analysis laboratory and confirm that  they can do the test and what they recommend as the proper procedure for collecting, handling and shipping a sample to the lab. (See list of laboratories on PM 1098A Forage Testing Laboratories.) Sudangrass or sorghum-sudangrass should never be used for horse pasture.

 

Is frosted alfalfa toxic?
Frost injured alfalfa, clovers, and the commonly used perennial cool-season forage grasses Do NOT have the potential to form hydrodynamic acid, are NOT considered toxic and can be safely grazed or harvested for hay or silage following a frost. There is probably a slightly higher bloat risk for grazed alfalfa and white clover the first  few days after a frost.  Follow normal bloat preventing grazing management when grazing alfalfa and clover.

The literature notes that Indiangrass (a perennial, warm-season prairie grass) and birdsfoot trefoil have a low potential to form Hydrocyannic acid.  Actual problem cases using these forages should be considered extremely rare and of minimal concern.

 

Should I harvest the last alfalfa cutting after the frost?
There is not a simple answer. In general, it will depend whether the frost was a "killing frost" or not.  A "killing frost" is not the first light frost of the season; rather, it is a 23 or 24 F degree freeze that lasts for 4 to 6 hours or so.

If the producer does not need the forage, it is best for the alfalfa plants to leave them uncut and standing through the winter.

If it was the hard, killing freeze, and the producer needs the forage, harvest as soon as possible after the freeze to salvage as much of the nutritive value as possible. The longer the delay, the greater the weathering damage and leaf loss from the standing frosted plants.  

If the frost were a light, non killing freeze, the tops of the alfalfa plants will be visibly damaged but will not likely stop growing for the season. The damaged tops will deteriorate in nutritive quality for the remainder of the autumn, but the plant will still be attempting to regrow from crown buds and will be using stored sugars. The best management for the plant is to allow it to continue to grow using whatever green leaf area it still has until the hard, killing freeze. Then if the producer needs the forage, it can be cut and harvested for hay or silage; or grazed.

Alfalfa plants cut immediately after a partial freeze (non-killing frost) and which experience further normal growing temperatures will start new re-growth from crown buds, using accumulated proteins and carbohydrates that would otherwise be used for over wintering and re-growth the following spring.  When these late-recovering plants experience a killing freeze a few days or weeks later, they will be physiologically weaker and more susceptible to winter injury.

 


 

Stephen K. Barnhart is a professor of agronomy with extension, teaching, and research responsibilities in forage production and management.

Deciding Between Grain and Forage Harvest for Late Maturing Soybeans

 

Stephen K. Barnhart and Palle Pedersen, Department of Agronomy

 

Irregular development and lateness of Iowa crops this year are cause for reflection as producers conduct late season evaluation of crops in individual fields, and plan when and how to harvest them for the greatest economic advantage. Late season evaluation involves reviewing normal crop growth and development, assessing the condition of the crops in individual fields relative to normal, and thinking through several autumn season scenarios such as: How will this field develop between now and the normal frost time?  What are the concerns or alternatives if a frost comes one or two weeks earlier than normal?


Soybeans
The Iowa soybean crop is intended for harvest as dry beans. The beans harvested from immature soybeans are often small, misshapen, off color and sometimes diseased.  The normal grain markets generally do not want immature soybeans and will pay greatly reduced prices for them. The harvest or use alternatives for immature soybeans are usually livestock grain or forage. It is also useful then to closely follow the development of the soybean crop.

 

The normal development and maturation of a soybean plant can also be reasonably tracked by several identifiable plant characteristics. The key characteristics and plant parts are the development of the pods and the beans in the pods, particularly those near the top of the plant.

 

Are soybeans safe from frost?

Most soybeans will have developed to R5 or greater by mid-September. Stage R5 gives the first indication of bean seed development in the upper part of the plant. At stage R5 small beans (one-eighth inch long) can be found in a pod attached to one of the four uppermost attachment points (nodes) of a fully developed leaf. Substantial bean yield losses are likely from a killing frost of soybeans in early R5. A University of Wisconsin study showed that there was about a 75 percent yield reduction when soybeans were killed at R5 and may cause bean quality problems ( green, odd shaped beans, etc,).

 

To escape significant bean quality problems, soybeans must reach developmental stage R6 before a hard killing freeze. Stage R6 is called the "full green bean" stage. A plant has reached this stage when there are full sized green beans filling the pod cavity of at least one pod at one of the four uppermost leaf attachment points (nodes) supporting a fully developed leaf. Even at stage R6 a freeze will cause some yield loss. In the Wisconsin study, soybean yield losses were 20 to 25 percent when the crop received a killing freeze at stage R6. 

 

A critical time for late developing soybean crop is the two week period required for the plant to develop completely through the R5 stage. If a killing freeze comes early in the R5 period, yield losses can be significant, but if the killing freeze comes late in the R5 period, yield loss risk is expected to be much reduced.

 

If one normal pod has attained its mature pod color (brown or tan) then the plant as a whole is considered to have reached complete pod fill and to be in the growth stage called physiological maturity ( R7). At this stage, it is common to have green, yellow and brown, or tan (depending on variety) pods on the same plant. This describes the beginning of developmental stage R7. At stage R7 the plant is considered to be near enough to maturity that a hard freeze will have little influence on its yield. 

 

Soybeans as a forage crop
When is it appropriate to abandon the little hope of much grain yield from the soybean crop and look to it as a possible forage source? The critical decision should be based on what developmental stage the majority of plants will reach by the time of a killing freeze. If the soybean plants will reach developmental stage R6 (full green bean stage) before a freeze, their value is far greater as a bean crop. If the freeze occurs when only small pods have formed near the top of the plant (pre stage R5) or there are only very small developing beans in upper pods (early stage R5), then harvesting of the crop for forage is more appropriate. By the time beans in the upper pods are about one-half to three-fourths full size (late stage R5), the advantage swings to harvest for beans but at a significantly reduced yield and the possibility that bean quality will be adversely affected.

 

The forage quality of soybean forage
When in its vegetative and early grain development stages, the soybean plant is very similar in feeding value and harvestable yield to that of more familiar forage legumes such as alfalfa or red clover. As with other forage plants, the developing stem becomes less digestible while the leaves, and in the case of the soybean, the pods and developing seed remain highly digestible. Data presented in Table 1 shows relative yields and nutritive characteristics of whole plant soybean forage at increasing stages of development. Note that while the protein and digestibility remain surprisingly constant over this range of harvest periods, the harvestable dry matter increases with maturity. Beyond R6, however, the leaf material will quickly be lost, leaving a forage material with a high proportion of high quality pods with beans and the remainder being very low quality, high fiber stems. The risk of pod and bean shatter loss also increases if soybeans are harvested much past R6.

 

Table 1. Yield and quality of soybean forage as affected by harvest maturity. (Univ. of Wisconsin).

Table 2 soybean maturity chart

 

Managing Soybeans for dry hay
Immature soybeans will have some of the same field curing challenges as would any other forage legume, with the stems drying more slowly than the leaves. Soybean leaves are very brittle when dry and can shatter excessively during raking and baling. While the use of a mechanical conditioner will speed the drying of stems, producers have found that flail conditioners lead to more leaf and pod losses than do roll-type conditioners. Frost will lead to leaf death and leaf drop within a few days, so if you are planning to use soybeans for forage be ready to cut, condition and windrow the crop. Soybean hay bales are subject to more rain and weathering loss if stored outside than are those of grass or alfalfa hay, so inside or covered storage is recommended.

 

Managing soybeans for silage
More soybean dry matter will be retained if soybeans can be stored as silage. The target moisture content for ensiling is 60 to 65 percent, so green soybean plants cut for silage  may require some field wilting before chopping. Drying conditions will dictate how long the wilt period should be. If wilted too long, the silage will be more difficult to pack, and you increase the risk increased dry matter loss from excessive respiration and heating during ensiling. Soybeans chopped and stored at higher than 70 percent moisture may undergo abnormal or incomplete fermentation and will begin to lose dry matter as seepage (effluent) losses.

 

Use caution when locating a site for silage storage with potential for seepage losses, because off-site movement of silage effluent can become an environmental hazard as a ground or surface water contamination source. It is very difficult to estimate the moisture content of immature or frosted soybeans. The best method is to chop a few feet into the field and send a representative sample of chopped forage to a test lab or use some other reliable method for moisture determination.

 

Additional cautions about using soybeans for forage
Review your herbicide labels for any restrictions regarding residues on the crop and feeding limitations. Soybean forage being stored as silage may ferment more favorable and attain a lower pH if it is inoculated with lactic acid bacteria inoculant. Several animal nutritionist say that very immature, green soybeans with only small pods and no appreciable bean formation can be fed as you would feed other legume forage. However, as the whole plant fat content increases with bean development, these nutritionists caution producers to limit the amounts fed daily to livestock. Check with a nutritionist when formulating rations containing soybean forage.

 

For more information on determining the development and satges of soybeans, see ISU Extension publication PM 1945 Soybean Growth and Development.


 

 

Stephen K. Barnhart is a professor of agronomy with extension, teaching, and research responsibilities in forage production and management. Palle Pedersen is an assistant professor of agronomy with research and extension responsibilities in soybean production.

 

 

Deciding Between Grain and Forage Harvest for Late Maturing Corn

Stephen K. Barnhart and Roger W. Elmore, Department of Agronomy

Irregular development and lateness of Iowa crops this year are cause for reflection as producers conduct late season evaluation of crops in individual fields, and plan when and how to harvest them for the greatest economic advantage. Late season evaluation involves reviewing normal crop growth and development, assessing the condition of the crops in individual fields relative to normal, and thinking through several autumn season scenarios such as: How will this field develop between now and the normal frost time?  What are the concerns or alternatives if a frost comes one or two weeks earlier than normal?

Corn
Most of the Iowa corn crop is intended for harvest as dry grain. If it will reach physiological maturity, it will be more valuable as harvested grain, but may require supplemental drying. If the field or parts of the field fall short of physiological maturity producers can harvest immature corn for silage or use it in grazing programs.

As the corn crop matures, harvestable grain yield will be highest at physiological maturity of the plant. However, highest yield of digestible nutrients as whole plant silage is greatest several days before plant maturity; when the stalk and leaf material remain more digestible.  Since the optimum silage harvest comes before grain crop maturity, it is important to have an accurate estimate of the developmental stage of the corn crop.

Visual Indicators of Corn Maturity
As the corn plant is nearing maturity, one of the best means of determining the developmental stage is an occasional look at the developing grain. As kernels mature, the milky, sugary endosperm gradually changes to a solid, starchy consistency. Soon after the grain reaches the "dent" stage, you can usually see the 'milk line' or the boundary between the liquid and solid endosperm.The milk line is easiest to see on the 'back' side of the kernel; the side opposite the embryo or "germ".  It is detectable as a relatively distinct line between two shades of yellow. Very soon after dent the milk line is nearest to the dented end of the kernel. As the grain develops the milk line can be seen nearer and nearer to the pointed tip of the kernel. At physiological maturity of the grain, the milk line has reached the tip of the kernel and a "black layer" forms at the tip indicating that all movement of nutrients from the stalk to the kernel have ceased. The grain and stalk continue to dry from that point on.

Table 1. summarizes several characteristics of the developing corn plant. As you review this table note that the greatest harvestable yield of whole plant digestible nutrients (TDN) is at a stage when the milk line has advanced about two-thirds of the distance from the dent to the kernel tip. If you have significant acreage of corn to chop, begin when the most advanced fields or parts of fields are at one-half milk line and try to harvest all the silage when between one-half milk line and maturity. Fortunately, the moisture of the whole plant is about 65 to 70 percent moisture at this stage; ideal moisture for direct chopping of corn for silage.

Table 1. Effect of harvest stage on yield and quality of corn silage.

immature corn table 1

So, in a “normal” maturity and dry-down season, the decision to chop whole plant corn silage has to be made fairly early. With late planted corn and late maturity risks, frost may force the decision to harvest as silage. If frost comes during the target milk line period, whole plant moisture content should be appropriate for normal ensiling. 

There are some ensiling considerations if frost comes when the crop has only reached early dent, or less. Whole plant silage chopped and stored at higher than 70 percent moisture may undergo abnormal or incomplete fermentation and will begin to lose dry matter as seepage (effluent) losses. Use caution when locating a site for silage storage with potential for seepage losses, because off-site movement of silage effluent can become an environmental hazard as a ground or surface water contamination source. It is very difficult to estimate the moisture content of frosted, immature corn. The best method is to chop a few feet into the field and send a representative sample of chopped forage to a test lab for moisture determination.

For more information on determining the development and stages of corn, see ISU Extension publication SR-0048 How a Corn Plant Develops.


 

 

Stephen K. Barnhart is a professor of agronomy with extension, teaching, and research responsibilities in forage production and management. Roger Elmore is a professor of agronomy with research and extension responsibilities in corn production.



This article was published originally on 10/13/2008 The information contained within the article may or may not be up to date depending on when you are accessing the information.


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