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osunpk

osunpk

Since 2008 I have served as the Precision Nutrient Management Extension Specialist for Oklahoma State University. I work in Wheat, Corn, Sorghum, Cotton, Soybean, Canola, Sweet Sorghum, Sesame, Pasture/Hay. My work focuses on providing information and tools to producers that will lead to improved nutrient management practices and increased profitability of Oklahoma production agriculture

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Sampling for pH and liming in continuous no-till fields

This article is written by Dr. David Mengel, Kansas State University Soil Fertility Specialist. 

One question that commonly comes up with continuous no-till operations is: “How deep should I sample soils for pH?” The next common question is: “How should the lime be applied if the soil is acidic and the field needs lime?”

Sampling depth in continuous no-till

First, sampling depth. Should two sets of samples be taken, at different depths?

Our standard recommendation for pH is to take one set of samples to a 6 inch depth. On continuous no-till fields where most or all of the nitrogen (N) is surface applied, we recommend taking a second sample to a 3-inch depth. We make the same recommendation for long-term pasture or grass hayfields, such as a bromegrass field that has been fertilized with urea annually for several years.

Nitrogen fertilizer is the primary driving force in lowering soil pH levels, so N application rates and methods must be considered when determining how deep to sample for pH. In no-till, the effects of N fertilizer on lowering pH are most pronounced in the area where the fertilizer is actually applied. In a tilled system, the applied N or acid produced through nitrification is mixed in through the action of tillage and distributed throughout the tilled area.

Where N sources such as urea or liquid UAN solutions are broadcast on the surface in no-till system, the pH effects of the acid formed by nitrification of the ammonium will be confined to the surface few inches of soil. Initially this may be just the top 1 to 2 inches but over time, and as N rates increase, the effect of acidity become more pronounced, and the pH drops at deeper depths. How deep and how quickly the acidity develops over time is primarily a function of N rate and soil CEC, or buffering capacity.

Where anhydrous ammonia is applied, or liquid UAN is knifed or coulter banded below the surface, an acid zone will develop deeper in the soil, usually 2-3 inches above the release point where the fertilizer is placed in the soil. So if the ammonia is injected 8 inches deep, there will be acid bands 5 to 8 inches below the soil surface. As with long-term surface applications, these bands will expand over time as more and more N fertilizer is placed in the same general area. The graphic below illustrates the effect of a high rate of ammonia placed in the same general area in the row middle on a high CEC soil for more than 20 years.

The actual depth of the acid zone in fields fertilized with ammonia gets tricky as application depth can vary depending on the tool used to apply the ammonia. Traditional shank applicators generally run 6 to 8 inches deep, so a sample for pH measurement could be taken at 3-6 inches or 5-8 inches deep, depending on how deep the shanks were run. The new low-disturbance applicators apply the ammonia 4-5 inches deep. A sweep plow or V-blade applies ammonia only 3-4 inches deep. So sampling depth for pH should really depend on where the acid-forming N fertilizer is put in the soil.

Mengel and West, Purdue Univ.

Mengel and West, Purdue Univ.

 

Liming application methods in continuous no-till

Now, where do you place the lime in continuous no-till? If you surface apply N, then surface apply the lime. That’s a simple but effective rule. But remember that surface-applied lime will likely only neutralize the acidity in the top 2-3 inches of soil. So if a producer hasn’t limed for 20 years of continuous no-till and has applied 100 to 150 pounds of N per year, there will probably be a 4-5 inch thick acid zone, and the bottom half of that zone may not be neutralized from surface-applied lime. So, if a producer is only able to neutralize the top 3 inches of a 5-inch deep surface zone of acid soil, would that suggest he needs to incorporate lime? Not really. Research has shown as long as the surface is in an appropriate range and the remainder of the acid soil is above pH 5, crops will do fine.

Liming benefits crop production in large part by reducing toxic aluminum, supplying calcium and magnesium, and enhancing the activity of some herbicides. Aluminum toxicity doesn’t occur until the soil pH is normally below 4.8. At that pH the Al in soil solution begins to increase dramatically as pH declines further. Aluminum is toxic to plant roots, and at worse the roots would not grow well in the remaining acid zone.

This implies that the acid zones from ammonia are probably not a major problem. We have monitored ammonia bands in the row middles of long-term no-till for many years and while the pH got very low, below 4.5, we never saw any adverse impacts on the crop that would justify liming and using tillage to incorporate the lime. In fact, some nutrients such as zinc, manganese, and iron can become more available at low pH, which can be an advantage at times.

Yield enhancement is not the only concern with low-pH soils, however. Herbicide effectiveness must also be considered. The most commonly used soil-applied herbicide impacted by pH is atrazine. As pH goes down, activity and hence performance goes down. So in acid soils weed control may be impacted. We do see that in corn and sorghum production.

Liming products for no-till

When choosing a liming product, is there any value to using dolomitic lime (which contains a large percentage of magnesium in addition to calcium) over a purely calcium-based lime product? On most of our soils in Kansas we are blessed with high magnesium content. So as long as we maintain a reasonable soil pH, there normally is enough magnesium present to supply the needs of a crop. Calcium content is normally significantly higher than magnesium, so calcium deficiency is very, very rare in Kansas. The soil pH would need to be below 4.5 before calcium deficiency would become an issue. Before calcium deficiency would occur, aluminum toxicity or manganese toxicity would be severely impacting crop growth. So producers really don’t have to worry about a deficiency of calcium or magnesium on most Kansas soils.

What about the use of pelletized lime as a pH management tool on no-till fields? The idea has been around for a while to use pel-lime in low doses to neutralize the acidity created from nitrogen and prevent acid zones from developing. There is no reason it won’t work, if you apply enough product each year. Pel-lime is a very high-quality product, normally having 1800 to 2000 pounds of effective calcium carbonate (ECC) per ton, and can be blended with fertilizers such as MAP or DAP or potash easily.

But it is costly. As an example, at a cost of $160 per ton and 1,800 lbs effective calcium carbonate (ECC) per ton, 100 pounds of ECC pel-lime costs $8.80. If it costs $25 per ton to buy, haul, and apply a 50% ECC limestone, that equates to $2.50 per 100 pounds ECC.

If you were applying 100 pounds of urea-based nitrogen, it would take approximately 180 pounds of ECC to neutralize the acidity produced by the N. This would require 200 pounds of 1,800 pound ECC pel-lime or 360 pounds of 50% ECC ag lime. The cost would be around $16 per acre with pel-lime or $4.50 per acre with ag lime. So technically, the pel-lime option is fine. But it would cost more than 3 times as much, at least in this example. You can use your own figures regarding costs and ECC of different lime products available to you to do a similar calculation. Deciding which product to use is a simple economic choice.

Summary

Applying N fertilizer to soil will cause the soil to become acidic over time. Placement of the applied N and the level of soil mixing done through tillage determine where the acid zones will develop.  Make sure your soil testing program is focused on the area in the soil becoming acidic, and apply the lime accordingly.

Dave Mengel
Kansas State University
Professor Soil Fertility Specialist
dmengel@ksu.edu

Results from 1st year of Soybean Starter Work

In the spring of 2014 we initiated what was to be the first year of a three year project evaluating starter fertilizers for soybean production in the southern Great Plains.  The first and second year was and is being funded by the Oklahoma Soybean Board.

Year one was a bit experimental in that with so many products on the market we needed some initial work to help focus the direction for years two and three.  I also added a treatment which I knew would have significant negative impact, for extension reasons.  Keep in mind two locations in a single year does not make an experiment nor provide enough information to draw a definite conclusion.   It is however enough to learn some lessons from and for us to plan for our 2015 trials.

The 2014 trial consisted of 12 treatments, Figure 1 and Figure 2.  In these treatments I wanted to see the impact of a standard practice, see if a specific nutrient may be more so beneficial, and evaluate a few popular products.  The spring of 2014 started out dry so at one of our two locations we pre-watered.  This was done by hauling water to the Lake Carl Blackwell (LCB) 1000 gallons at a time and pumping through sprinklers.  The other site, Perkins, we delayed planting until we had moisture.

Treatment Structure and rates for the 1st year of the Soybean Starter Study.

Treatment Structure and rates for the 1st year of the Soybean Starter Study.

List of fertilizers and products used.

List of fertilizers and products used.

Image taken while planting the Soybean Starter study at Perkins.  A CO2 system was used to deliver starter fertilizers with seed.

Image taken while planting the Soybean Starter study at Perkins. A CO2 system was used to deliver starter fertilizers with seed.

The two locations were also selected due to differences in soil fertility.  The LCB site is has good soil fertility, with exception of phosphorus (P), and the Perkins site pH was an issue.  I would have expected a benefit from adding P at both of these locations.  Figure 4 shows the soil test results.

Soil Test results from LCB and Perkins.

Soil Test results from LCB and Perkins.

At LCB as expected some of the treatments (Thio-Sul) reduced stand, some unexpectedly reduced stand (Fe) and others had less impact on stand (APP 5.0) than expected.  The growth at LCB was tremendous, the 30 in rows covered over very quickly and the majority of the treatments hit me waist high by early August (I am 6’0”).  Many of the treatments showed greater growth than check.  But when it comes down to it, grain pays and green does not.  Statistically there were no treatments that out preformed the un-treated check, however the K-Leaf and 9-18-9 did make 3 and 2 bpa more than the check respectively.  What I am hypothesizing at this site is that the added nutrients, especially those with high P levels, significantly increased vegetative grown and these big plants were delayed into going reproductive and they started setting pods later in much hotter weather.  While riding in the combine I could see that the plots with compact plants with clearly defined rows out yielded those were the vines had crossed over and we harvested through more of a solid mat of mature plants.  A hot August is not uncommon and I am curious on whether this trend repeats itself.  If it does this may direct us into research evaluating ways to force/promote the reproductive stage to start in these big plants.  Even if we can force flowering to start earlier, it’s unknown whether yields will increase or not.

Yield and Stand counts from the 2014 LCB Soybean Starter Study.

Yield and Stand counts from the 2014 LCB Soybean Starter Study.

The Check plot at LCB were plants noticeably a bit smaller and more yellow than the neighbors with phosphorus.

The Check plot at LCB were plants noticeably a bit smaller and more yellow than the neighbors with phosphorus.

Soybeans at LCB on August 4th.

Soybeans at LCB on August 4th.

The same trends in treatments reducing stand can be seen at Perkins, however the impact was less extreme.  Perkins being planted later due to waiting on moisture forced a later flowering date and I believe reduced overall yields.  But the addition of P at this low pH site definitely made a difference.  While again no treatments were statistically greater than the un-treated check the 2.5 gpa APP, DAP broadcast, APP/H2O, and Pro-Germ/H20 treatments increased yield by 5.6, 4.2, 3.8 and 1.7 bpa respectively.

Yield and Stand Counts from the Perkins 2014 Soybean Starter Study.

Yield and Stand Counts from the Perkins 2014 Soybean Starter Study.

Take home from year one was that at LCB the addition of a starter fertilizer had little benefit and if done wrong could cost you yield while at the low pH site of Perkins an addition 2.5 gallons of APP did get a 5 bpa bump, but do to variability in the trial the increase was not statistically significant.  This year we will drop some of the treatments and incorporate a few new treatments.   Based on the current weather we look to potentially being able to start with better soil moisture at planting.  Again do not take this work and significantly adjust any plans you have for your 2015 soybean crop. This is however some interesting findings that I wanted to share and make everyone aware of.  Finally thank you to the Oklahoma Soybean Board for providing funding for this work. www.oksoy.org/