Dec 2011 Volume 37 | Issue 6

DOUBLE-CHECK SOIL PROBE SPRAYS

-Fred Vocasek, Senior Lab Agronomist, 22 December 2011


Wet or clayey soil can be hard to sample because it sticks to the sides of the soil probe tube, making it hard to remove the soil core. We have always recommended spraying the inside of the tube with WD-40, as needed. This kept the soil from jamming up inside the tube and also let the core slip out smoothly. It didn’t seem to affect any of the routine soil test values, including organic matter.

There are alternatives to WD-40, but one of our Laboratory customers just alerted us to a potential problem. They took about 40 soil samples and sent them in for analysis. The results for phosphorus and some other results didn’t correspond with the field history results. They repulled and resubmitted the samples, with better results.

After doing some detective work, the company agronomist found that the samplers had used a commercial product that was promoted as being the same as WD-40. It was - if it was being used as a machinery or equipment lubricant. The agronomist quizzed the factory rep, finding out that the product apparently contained phosphorus and metals which may possibly have affected the soil sample.

Spray lubricants are mixtures of light-weight petroleum compounds, surfactants, and other ingredients. To date, we are not aware of contamination problems from WD-40. A 1995 study by Univ. of Wyoming compared WD-40, PAM vegetable spray, Dove dishwashing liquid, motor oil, and silicone spray. They found low nutrient levels in each of the materials. There were slight changes in some soil test levels, but were thought to result from complexing or chelating properties of the lubricant mixtures.

Overall, WD-40 seemed to perform well in this study. The final thought was that a sampler would have to use enough WD-40 to physically dilute the soil sample to have a serious effect on soil test results. We would advise caution when using an alternative product as a soil probe lubricant.


Soil Nitrate Accumulates During Drought, Hot Weather
-Fred Vocasek, Senior Lab Agronomist, 12 August 2011

The severe drought conditions and hot weather of summer 2011 may have an unexpected benefit - more soil nitrate. Soil nitrate levels of 100 lb N per acre or more are not uncommon following a summer like 2011. There are three main reasons that soil nitrates may accumulate: 1) reduced crop uptake, 2) less leaching, and 3) more mineralization.

1. Reduced crop uptake

Crops typically take up most of their nitrogen requirement during the vegetative growth stage. The uptake rate drops off quickly when the plant reaches the reproductive stages. If drought conditions hurt yield potential before pollination or bloom, some fraction of the soil nitrate is taken up and the rest stays behind to accumulate in the soil.

Nitrate accumulations are common for dryland or non-irrigated crops, but nitrate can also accumulate under irrigated crops with normal or above-normal yields. This can occur because of accelerated nitrogen mineralization caused by the hot weather. The amount of nitrogen mineralized can exceed the crop nitrogen removal, so the excess nitrate accumulates in the soil.

2. Less leaching

Nitrate can be transported or leached from an upper soil zone to a lower soil zone, depending on the amount of water that is able to percolate through the profile. Excess soil water will drain to lower depths, even if it is only a slight amount of excess. The leaching depth and amount of nitrate transported is affect by many factors. Factors which change constantly.

Higher evaporation rates and increased crop water demand during drought prevent excess water from accumulating in the upper root zone. For example, the total evapotranspiration vs. rainfall data from the Lubbock area (April-July) shows the net water loss to the atmosphere during summer 2011 was at least ten inches greater than the four previous years1. There was little or no opportunity for water to accumulate in the profile.

Nitrate remains in the upper soil profile simply because little or no leaching occurs during hot, dry conditions. There could be the same total amount of nitrate in the root zone, but a larger fraction of the total will be found nearer the surface during drought years. This accumulation pattern tends to skew soil sample histories, especially if one depends only on surface sample results for making nitrogen fertilizer recommendations. Collecting subsoil nitrate samples takes more time and energy, but will give a better idea of overall nitrogen fertility through the profile.

3. More mineralization

Total accumulations

Mineralization of organic nitrogen to nitrate is most rapid at high soil temperatures and with adequate soil moisture. Part of the nitrate accumulated during the growing season comes from the conversion of organic nitrogen found in the crop residue. In the case of wheat, about 5 to 7 lb N can be mineralized for every ten bushels of yield if the nitrogen in the straw is completely mineralized.

Much nitrate can accumulate from organic matter mineralization, even under what seem to be bad conditions. Nitrogen credits of 10 to 20 pounds of nitrogen per percent of organic matter are not uncommon under normal conditions. These are average numbers, but the actual nitrogen credit can be much higher under drought conditions. These credits have been documented in the Great Plains and other areas. 1

Note: Weather data from other drought-affected areas may be different than the Lubbock data, but the general trends would be similar.

Table 2 shows the nitrate that accumulated during the uncropped, fallow period at Alliance, Nebraska, for twelve different years. Soil samples were taken in the fall, either prior to or just after wheat seeding. In seven years out of twelve, the soil mineralized at least 70 lb N/ac, even when no nitrogen was applied (column a). Note that the highest amount of nitrate accumulated was during the 1980 season - one with widespread drought conditions very similar to those that occurred in 2011.

When an extra 40 lb N/ac was applied to the preceding wheat crop, the soil nitrate exceeded 70 lb N/ac in nine of twelve years (column b). However the amount of extra nitrate found in the soil test could not be entirely attributed to carryover fertilizer alone.

In another set of experiments, a Weld silt loam (Akron, Colorado) had a three-year average nitrate accumulation of 106 lb N/ac with no N applied and a Holdrege silt loam (North Platte, Nebraska) had a five-year average accumulation of 110 lb N/ac with no nitrogen applied.

Timing of accumulations

Much of the nitrate found in these situations accumulated in July and August, months that typically have the highest temperatures and lowest rainfall. Table 3 illustrates the pattern of nitrate accumulation during the fallow season for two of the Alliance sites. The Duroc soil was broken out of native sod in 1970, the Alliance soil was broken out of wheatgrass pasture in 1969. Nitrate mineralization was slow right after harvest and during early spring, but preceded rapidly during late July and August. In fact, the researchers found that soil samples taken in July might only contain 50% to 60% of the nitrate found at wheat seeding time.

Temperature has a huge effect on the microbes responsible for mineralizing organic nitrogen to nitrate. Figures 1 and 2 shows the effect of temperature on nitrification. Nitrate accumulated faster in warm soils than in cool soils. Figure 1 shows that nitrate accumulated to a concentration of 50 ppm about three weeks sooner at a summer-time 86/F soil temperature than at a spring-time 61/F soil temperature.

Figure 2 contains the same data as Figure 1, except the calendar days were converted to degree days. Nitrate accumulated to 50 ppm at roughly 450 degree days for all soils at all temperatures. Degree days are a more accurate way of helping define the rate of biological processes, including plant growth, insect development, and microbial processes. Degree days accumulate more rapidly in hot years than in normal years, so the rate and extent of nitrification increases as well because the microbes are more active.

The increased microbial activity helps account for the soil nitrate accumulations found after irrigated corn harvest, even during years when yields are high. Degree days accumulate quickly when air temperatures are high. Corn matures earlier, reaches senescence earlier, loses leaf canopy earlier, and quits taking up soil nitrate earlier in these situations. Leaf loss allows sunlight to penetrate and warms the underlying soils earlier than normal. This extends the time for optimum microbial activity, including the nitrification process. Thus, soil nitrates accumulate, especially if there is no rain or irrigation to move the nitrates deeper into the profile.

Summary

Soil nitrates often accumulate under high temperatures and drought conditions. Soil nitrate accumulations may be due in part to lower yields, less nitrogen uptake, and less water percolating through the profile. Don't dismiss the nitrate contribution from soil organic matter mineralization in these situations - whether under irrigated or non-irrigated conditions. The nitrification rate is related to the rate of degree day accumulation, both of which are more rapid under higher temperatures.

Soils are "alive" and their activity changes with changing weather. Not all of the changes in the nitrate soil test are due strictly to our fertilizer applications or lack of applications. In the words of a famous agronomist, "Man, you ain't raisin' those crops on styrofoam - you're raisin' ‘em on soil".

References:

Honneycutt, Cw.W., L.G. Potaro, and W.A. Halteman. 1991. Predicting nitrate formation from soil, fertilizer, crop residue, and sludge with thermal units. Journ. of Env. Quality. 20:850-856.
Lamb, J.A., G.A. Peterson, and C.R. Fenster. 1985. Fallow nitrate accumulation in a wheat-fallow rotation as affected by tillage system. Agron. Journ. 49:1441-1446.
Smika, D.E., A.L. Black, and B.W. Greb. 1969. Soil nitrate, soil water, and grain yields in a wheat-fallow rotation in the Great Plains as influenced by straw mulch. Agron. Journ. 61:785-787.
Texas AgriLife Extension. 2011. TexasET Network. Lubbock Weather Station data, http://texaset.tamu.edu/ accessed 08/11/11.


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Scholarships Awarded

Servi-Tech employs between 25 and 35 college students each summer as crop service interns. These students normally have an agricultural, or closely-related, major. Servi-Tech has a scholarship program that provides monetary awards to recipients selected from our pool of summer interns. Many past scholarship award winners have eventually become full-time Servi-Tech employees upon graduation.

A committee of Servi-Tech employees reviews the applications, and determines the number and amount of scholarship awards. For the 2009-2010 school year, a total of $11,000 has been awarded to twelve of our 2009 summer interns, which are listed at the left.


Congratulations to all the scholarship recipients!


Student University Award
Aaron Ehlers University of Nebraska $1250
Bryan Meister Central Community College $1000
Denton Bailey Kansas State University $1000
Zach Turner Missouri State University $1000
Keanan Kroetsch Fort Hays State University $1000
Casey Robinson Chadron State University $1000
Kyle O'Donnell University of Wyoming $1000
Eric Preston Kansas State University $750
Zehren Walker Colorado State University $750
Rebecca Duensing University of Nebraska $750
Mike Murch Iowa State University $750
Kyle Cushard Missouri State University $750


Second Guessing
-Rick Runyan;Ainsworth,NE


As harvest approaches, there is considerable speculation as to what the yields will be. We sometimes start to second guess our past management decisions of the growing season. Two of the most frequently second guessed are: did we under-apply nitrogen, and did we apply enough irrigation at the tail end of the season?

Those of us who have been involved in production agriculture for many years know that final yield depends on many things. If we did everything right from planting, adequate fertility, timely pest control, and water management, we would expect bumper crops. In reality that is not always the case. What does have a huge impact on final yield is the amount of Langley’s we receive throughout grain fill. Langley is a unit of measure that accounts for the amount of solar radiation received. We are looking for uninterrupted sunshine from pollination to black layer. Even hazy days, though not as detrimental as cloudy days, can play a huge impact. In those years when stalk rot is common, ear tip fill is poor, or when kernel depth is shallow, a lack of solar radiation during grain fill is often the primary cause. We see that same scenario play out after a hail storm. In this case we may have the solar radiation, but not enough leaf area to capture it.

As we move into harvest and start to evaluate things like hybrid selection, fertility programs, fungicide applications, and water management schemes, add the Langley’s accumulation to the notebook.


Estimating Harvest Loss

by Jeff Kugler;York, NE

Every fall as the combines head to the field, a few minutes are spent estimating whether the combine is doing an adequate job or if adjustments are needed to decrease grain loss. Making a rough estimate of how much grain is left behind in a harvested field can be accomplished with a few simple steps.

Step 1. Lay a 1 foot by 1 foot (inside dimension) box on the ground and count the seeds found within the box. To improve the accuracy of the estimate, three counts (one behind the left side of the header, one behind the center of the combine, and one behind the right side of the header) are better.

Step 2. Average your findings to determine the average number of seeds there are per sq ft. When estimating loss, we need to determine how many seeds there are per bushel. Assume for corn there are 90,000 seeds/bushel; soybeans 180,000 seeds/bushel; and milo 756,000 seeds/bushel. Seed size will influence the final results.

Once the counts have been taken and the results are in, take the average number of seeds/sq ft and multiply by 43,560 sq ft/acre, and then divide by the determined number of seeds/bushel.
Example: average corn counts were (4.5 seeds/sq ft) x (43,560 sq ft/acre)/90,000 seeds/bushel = 2.18 bushel/acre loss.

To confirm the harvest loss has been caused by the combine, check the un-harvested part of the field to determine if any loss has occurred prior to combining. There can be a storm event before harvest that will cause grain shattering.
When determining harvest loss from corn ear loss, remember that an average corn ear will have between 550 and 650 kernels.


Weed Control
by Kirk Rice; Weskan,KS


Usually when one thinks of weed control, it is for in-season control. Weed control is just as important in fallow and stopping mechanical weed dispersal.
An excellent and less expensive time to control weeds is after harvest. You don’t have to worry about crop safety and you can put down a residual that won’t affect a growing crop. Many troublesome weeds grow really well in wheat stubble after harvest. Canada thistle, bindweed, sandburs, Palmer amaranth, nightshade, velvetleaf and bur ragweed are just a few that can be effectively controlled off season. Soil moisture can be saved and a better seedbed preserved for the next crop. Perennials like Canada thistle and bindweed can be treated following corn or milo harvest, if conditions are acceptable. Control is more effective in the fall when perennials are sending carbohydrates to the roots getting ready for winter dormancy.
Another form of weed control that is less often thought of is combine sanitation between fields. Over the years it is obvious that many hard-to-control weeds are spread by combines. We have seen velvetleaf, Canada thistle and nightshade spread from field to field due to weeds in and on the combine. If there is a problem weed in one or more of your fields, try to take the time to clean the combine prior to changing fields. It isn’t the only reason those weeds are moving, but it is a major one. If custom harvesting is done, ask them to make sure their combines are cleaned out.

Remember there is more than one way to control weeds. Check with your Servi-Tech agronomist for help with ideas for herbicides for your off-season weed control.


Getting Ready For 2010

by Monte Roetman; Kearney,NE

With harvest time just around the corner, now is a great time to plan for the next crop season. It’s probably toward the bottom of the list of things to do this fall, but it is important to look closely at hybrid and variety selection now and order early to get the best selections and discounts from the seed companies.

The best thing, is to take note of the different hybrids that you have and record data such as: late season plant health, disease type and pressure, stalk rot issues and insect problems. Taking notice of these areas can help identify any problem areas and help to select a hybrid to combat or minimize problems for next season. In addition to your personal observations, review your consultant’s weekly reports to make sure nothing is overlooked when making a decision for next year. It can also help to attend neighborhood or area plot tours to personally observe some of the new technologies and hybrids that are coming available.

These steps should be taken whether planting corn or any other crop that you have in your farming operation. A little time invested early this fall can pay huge dividends a year from now when another harvest is about to begin.


The Cost of Volunteer Corn
by Bryan Boroughs; Cimarron,KS

No-till dryland cropping systems have been widely adopted across the western Great Plains for conservation and increased yield benefits for many years. This system normally follows a wheat - row crop - fallow rotation, with grain sorghum or corn being the typical row crop, although sunflowers are included in some locations. Corn, with the Roundup Ready genetics, is by far the preferred choice in these cropping systems in the corn rotation because of the advantages of using glyphosate herbicide with its broad spectrum weed control. One of the challenges of using this technology is the moisture depleting affects of the Roundup Ready volunteer corn in the no-till rotation. Glyphosate, 2,4-D, and dicamba are typically used as a burn down herbicide in fallow treatments, but these obviously have no effect on the volunteer corn. Although producers can fall back on tillage to control the volunteer, that is not always the desirable option when moisture and soil tilth benefits of no-till are the primary goals of the cropping system.

Researchers from Kansas State University are conducting a three year study to determine the moisture loss from volunteer Roundup Ready corn during the fallow period and its negative effects on wheat. The study also hopes to determine the density of volunteer corn where it becomes profitable to use chemical control methods on the volunteer. There is now data from the first two years of the study with the final year of the study planned for the 2009-2010 cropping season. The study is being conducted at locations in Garden City, Colby and Tribune, Kansas. The study is set up in a randomized block design evaluating eight corn densities from 0-8000 plants per acre. All other weeds except the volunteer corn are killed and the soil moisture is determined in the profile to a total depth of five feet. This is measured before and after the growth of the corn. Wheat is then planted in the fall in the volunteer corn plots. Producer fields in the Garden City area have been sampled to try and determine the common corn densities in this cropping system under field conditions.

Although only two years of data have been obtained so far, some early conclusions from the research are that for every 200 volunteer plants, there was a one bushel per acre loss in wheat yield at Colby, and at Tribune there was one bushel per acre in yield loss from 75 volunteer corn plants. The scouting found that the average producer field had 455 volunteer corn plants per acre which would lead to an expected yield loss of 4.3 bushels of wheat. The researchers then calculated that if the wheat price was $5.00 per bushel, it would take about 250 volunteer corn plants per acre to break even, assuming a selective herbicide application of $14.00 per acre, using products labeled for volunteer corn control such as Select, Assure II, or Poast Plus. The breakeven cost would change based on the expected price of wheat or a change in the herbicide cost and application charge. The researchers also noted that the cost could be affected by whether the field could be spot sprayed or not. Information for this article is credited to the Kansas State University Field Day 2009, Report of Progress 1014 and the Southwest Research-Extension Center.


Yield Mapping with GPS

by Andrew Vrbka;Geneva, NE

Many producers are using GPS in their combines to map yield patterns across the field at harvest. During the winter months, you may choose to print these maps. Some may be shown to your agronomist to see how well a hybrid or a field did, but many will be filed away, never to be seen again. What should you do with yield maps?

A good idea is to print these maps out as soon as harvest is complete. Make some additional copies and share these with your Servi-Tech agronomist. As you review these maps with your agronomist, look for areas of higher yields and lower yields. If possible, compare your yield maps with a soil type map and grid sample maps. Select areas of the field to soil sample separately to identify possible fertility problems. You may also identify areas that may benefit from higher seeding populations, or maybe you can plant fewer seeds, and maintain the yield potential in areas of the field.

After you transfer your yield files to the computer, do not delete the controller card to use again next year. Instead, use a new controller card every year. This will prevent down time or loss of information from a bad card. The more you use a pc card, delecite and record information to the card, the more likely you will have a card go bad. Take the card after harvest, write the year on it, and store in your files. This will also be helpful should you have any problems with your computer and lose information. Also, you have quick access to files should you need historical yield data at a later date.
Have a safe and successful harvest.




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