Ag Connection

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Volume 4, Number 6
June 1998
This Month in Ag Connection
No-Till Lime Management and Soil Sampling
Pelletized Lime - Packaged for Marketing
European Corn Borer
Conservation Tillage Does Not Increase Soybean Diseases

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No-Till Lime Management and Soil Sampling

Why shallow soil sampling is useful for no-till

The lack of soil mixing in no-till cropping systems creates a condition not found in tilled systems — stratification. Stratification is a layering effect, with conditions in the top inch or two much different than conditions below due to accumulation of crop residues and surface-applied fertilizer and lime.

This layering has led many people to suggest that we should just be sampling the top nutrient-enriched layer when soil sampling in no-till. There are two problems with this idea:

  1. Current fertilizer recommendations are based on research using soil samples taken to a depth of six inches. Accurate fertilizer recommendations based on shallower soil sample depths would require extensive research over many years.
  2. The shallow sample may not do as good of a job of accounting for nutrient availability in the crop rooting zone. Consider this example:
Sample Depth Soil A: Soil B:
Top 2" 20 ppm Bray P1 20 ppm Bray P1
2-6" 4 ppm Bray P1 15 ppm Bray P1
For soil A, the 0-6" sample gives a result of 9. A crop is much more likely to respond to a P fertilizer application on soil A than on soil B, but the 2-inch sample says that they’re the same. The six-inch sample shows the difference.

Soil pH right at the surface is important to herbicide behavior in no-till cropping systems. Consequently, soil pH is the one parameter for which a shallow sample makes sense.

Surface acidification

The four major N fertilizer sources all generate the same amount of acidity during the process in which ammonium is converted to nitrate. If surface applications of N fertilizer have been made, acidification will concentrate in the top one or two inches of the soil. If the salt pH (pHs) of a six-inch sample is 5.3, it’s likely that the pHs of the top inch may be in the range of 4.5 to 4.8 (normal recommendation is to lime when the six-inch pHs drops below 5.5).

With a surface pHs of 4.5 to 4.8, triazine herbicide activity would be reduced (especially Atrazine and Atrazine mixes). These herbicides, when surface-applied in no-till systems, are active mainly in this top inch of soil where low pH may occur and reduce their effectiveness.

Another consequence of low surface soil pH can be carryover problems with Pursuit and Scepter. These herbicides are strongly attached to soil particles at low pH levels, so they will tend to stay in this low pH surface zone. They are not as easily degraded when attached to soil particles, so their half-life becomes longer and the possibility of carryover damage to the next crop increases.

To the Other Extreme

The pH of the surface soil (1 to 2 inch depth) will increase and decrease faster than the soil in the top 6 inch layer. If you are liming no-till fields as soon as the surface pH is down to 5.0 and put down the typical two tons/acre, this will bump the pH of the surface one inch up into the 8.0 range for almost all soils in Missouri. One ton of ENM 450 lime will bump the pH of the surface inch from 5.0 to slightly above 7 for most Missouri soils. This big jump in surface soil pH can create negative effects with some herbicides.

Several of the sulfonylurea herbicides degrade slowly under high pH conditions and are likely to carry over and damage the following crop. Classic and its mixes (Canopy, Canopy XL, Authority Broadleaf) are not labeled for use above pH 7.0, and Peak and Exceed are not labeled for use above pH 7.8 (these are water pH values which are about 0.5 pH units higher than the salt pH).

In order to minimize carryover problems with sulfonylurea and triazine herbicides, make smaller lime applications and monitor the pH of the surface soil after liming. While more costly on a ENM basis, pelletized lime may be a better choice for reduced lime application rates. If the surface soil pH goes too high, do not use herbicides that are restricted at that pH, and use lower lime rates the next time you apply lime.

Another reason to keep the pH of the top inch from getting too high is that high pH will increase volatilization losses from surface-applied N fertilizer. A good target here would be to keep surface pHs below 7.5. Above this pHs, even the ammonium from ammonium nitrate can be volatilized.

Author:  Peter Scharf and Bill Johnson, UMC Agronomy Extension

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Pelletized Lime - Packaged for Marketing

The effectiveness of any agricultural lime product is dependent on the neutralizing ability of the lime, which is a function of two factors — the fineness of the lime’s particle size and its purity. The finer the particle size and the higher the purity, the more effective the lime.

Pelletized lime is simply finely ground lime which has been formed into pellets (packages) using a lignosulfonate binder. When these pellets come into contact with moisture, they disintegrate, making the lime available for neutralizing the soil.

The primary issues to consider are:

  1. Is the pelletized lime more effective?
  2. Is it faster acting than bulk agricultural lime?

Research indicates pelletized lime, as with bulk agricultural lime, is only as effective as its stated "effective neutralizing material" (ENM) and it’s speed of reaction is not any faster. In fact, research conducted by Michigan State University in 1995 and 1996 revealed that bulk agricultural lime raised the soil pH notably faster than pelletized lime. Researchers attributed these results to the different distribution pattern of pelletized lime and binding agent used in making the pellets. Tests for change in pH were made at weeks 1, 2, 6, 8, and 16.

Pelletized lime is simply a differentiated form of agricultural bulk lime, packaged for easier handling, distribution and spreading. Decisions on which form of lime to use need to be made on the basis of cost, convenience, and ENM.

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European Corn Borer

Biological facts for European corn borers:
  • moths live 1 to 2 weeks
  • preoviposition (before egg laying begins) lasts 2 to 3 days
  • moths lay eggs for 7 to 10 days
  • a single egg mass contains 23 eggs (average)
  • each female moth lays 400 eggs (approximately)
  • eggs hatch in 3 to 7 days (4 to 6 days is more typical)
  • larval survival rate is 8% to 20%, depending on weather conditions.

Immature ECB development at 70 F:
first instar -- 4 days
second instar -- 4 days
*third instar  -- 4 days
fourth instar -- 4 days
fifth instar -- 10 days
pupal stage -- 12 days

*Between the third and fourth instar, the ECB migrate from the whorl to boring in the stalk. After the larvae are in the stalk, they can not be controlled by pesticide applications.

European corn borer (ECB) overwinter in Missouri as full grown larvae and can be found in last year’s corn fields, protected within the old stalks. The corn borer progresses from larvae to pupae to adult moth. Finding empty pupal cases in the field allows observers to estimate when to search for egg masses and, consequently, when the new larvae will be attacking knee high corn.Since the borers live in Missouri all year, local weather conditions such as thunder storms, high winds, and cool nights will have a detrimental effect on larval and pupal development, moth survival, egg laying and egg survival. Even though the timing of important life stages are known, surveys of corn fields are the only way to determine the seriousness of ECB infestations.

When the dates for egg laying are predicted for your area, begin looking for egg masses on the undersides of corn leaves in the tallest, earliest planted fields. This is the preliminary step in scouting for ECB. It is easier to see the feeding damage on the corn leaves, but the timing of the egg survey gives an earlier warning sign of a potential economically damaging infestation.

After the eggs hatch, the borers crawl into the whorl to begin feeding. This early leaf feeding damage is marked by small round holes. Initially, the holes may not go completely through the leaf. ECB leaf feeding injury is commonly called shot-hole damage. Corn plants with less than 16 inches extended leaf height are toxic to the ECB. Still, corn grows quickly at this stage and the only way to confirm a borer infestation is to scout the fields. When eggs, newly hatched larvae, or feeding injury are detected it is time to begin scouting in earnest.

To do a thorough job of scouting, select 5 survey sites per field. Avoid scouting outside rows, especially those adjacent to grassy margins or waterways, where ECB numbers may be higher than within the field. At each survey site within the field, randomly choose the beginning corn plant for the survey. Count the number of corn plants with either egg masses or leaf feeding from 20 consecutive plants. Repeat this process for all survey sites in the field. Determine the percent of infested plants out of the 100 plants surveyed.

If leaf feeding is seen, select the first two damaged plants from each survey site and dissect them to determine the number of borers per plant. Storms, predators, and feeding resistance factors may kill ECB larvae shortly after they have fed on the leaves. There is no need to treat if there are few living larvae remaining in the corn plants.

Authors: Jim Jarman, Agronomy Specialist, Anastasia Becker MU Research Specialist, IPM and Maureen O’Day, MU Extension Associate, IPM

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Conservation Tillage Does Not Increase Soybean Diseases

The increased amount of plant residue left on the surface by conservation tillage has raised a concern of increased soybean disease problems. Research in Indiana and Argentina, indicated that conservation tillage conditions could increase incidences of phytopthora root-rot, sudden death syndrome and seedling diseases. However, a three-year study in central Missouri and a six-year study in both north-central and southeast Missouri, determined soybean disease severity was similar between disc-till and no-till plots.

Sudden death syndrome was slightly more severe in no-till than disc-till in the southeast Missouri study. Otherwise, none of the soybean diseases increased under no-till or conservation tillage conditions. This does not mean farmers should relax their concerns about soybean diseases. Farmers should plant varieties resistant to the most prevalent diseases in their area and rotate crops to avoid disease problems.

According to the Missouri studies, soybean farmers who are using or are considering no-till production, should not be concerned about increasing problems due to charcoal rot and several other diseases. In fact, brown spot and bacterial blight were found to be less severe under conservation tillage conditions. Additionally, data from the southeast Missouri site indicates that soybean cyst nematode population growth is inhibited by conservation tillage.

Author: Joe Marks, Source: Al Wrather, MU Entomologist and Bill Wiebold, MU Agronomist

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University of Missouri ExtensionAg Connection - June 1998 -- Revised: April 20, 2004