Soil sample pointers

Written by Dr. Jason Weirich on .

Every year I get questions that focus on fertility. My first response is to ask, “Have you pulled a soil sample?” The typical response I get is, “I think so.”

Just what role should soil testing play in your farming operation?

Soil sampling is not a perfect science. However, it can be a valuable component of your agronomy programs by following a few basic principles.

The standard soil sampling depth is six to seven inches. This depth represents approximately two million pounds of soil—a convenient conversion number. I recommend that you stay close to this depth. Equations that soil testing labs use were developed with that standard depth.

You need a strategy for sampling fields. The general rule of thumb is a “composite” soil sample is not to be greater than 20 acres.

For example: an 80-acre field needs four separate soil samples. Try to divide sampling areas from fields greater than 20 acres into a management zone. These zones can be based upon soil type, history, yield potential, field geography, field use or other logical divisions.

Each composite sample should have 12 to 25 soil cores. This allows you to collect a representative soil sample from that area. Fewer than 12 cores per sample can lead to poor representation if one of the cores is extremely high or low in a given nutrient. If you have banded any fertilizer applications, you must have at least 20 cores per sample.

Another question I often get is, “How often should I resample?”

I suggest every two to four years, depending upon the crop grown, fertilizer utilized, environmental conditions and other agronomic components. Try to resample fields the same time of year, and preferably after the same cropping sequence.

Precision agriculture programs usually sample in a tighter acreage pattern. Some programs use standardized grid samples while others use management zones. Most grid sampling is done on 2.5-acre grids. MFA’s precision program often offers a combination of composite, grid and management zone sampling. This provides producers with the ability to apply the right amount of nutrients to the right acre, and it gives growers a great range of agronomic and economic options. Contact your local MFA to see how MFA’s precision program can help you and your farm increase profits.

Regardless of the collection process you choose, basic soil sampling procedures should be followed. Consistency is the key to an effective soil-sampling program.

Even if you follow these simple guidelines there may be anomalies associated with soil testing. Don’t get frustrated if some of your soil tests come back different than expected or are inconsistent across space or time.

Soil is a complex combination of physical, mineral, biological and organic residue systems working together. Some unexpected measurements will come along.

Soil sampling is just one component of crop nutrient management. On page 10 of this magazine, MFA agronomist Steve Cromley discusses nutrient recommendation programs.

Dr. Jason Weirich is director of agronomy for MFA Incorporated.   See related story on interpreting soil samples HERE.

Nutrient level tune-up

Written by Steve Cromley on .

On page 8 of this issue, Dr. Weirich discussed the importance and techniques for collecting a proper soil sample. The next step in developing a nutrient management plan for your farm is interpreting the soil test results.
Soil testing and nutrient management is not an exact science. Do not get lost in the numbers on your soil test report. Instead, pay attention to the soil test ratings or levels of each nutrient. If a nutrient level is very low on the soil test report there is a high probability that a positive yield response will occur from applying that nutrient to the planned crop. Likewise if a nutrient rating on the soil test is very high there is a low probability that the planned crop will respond to fertilizer applications of that nutrient. Soil tests are more accurate at determining pH, phosphorus and potassium levels then secondary or micronutrient levels. If a secondary or micronutrient is low on the soil test report consider using a plant tissue test to confirm a deficiency. You may also consider on farm trials by applying the secondary or micronutrient in question to a small area in the field.

Once you have determined which nutrients need to be applied to maximize yields, the next step is to determine an application strategy. Most fertilizer recommendations including MFA’s are based upon a build-plus-maintenance approach. The goal of a build-plus-maintenance strategy is to increase low-testing nutrients to optimal levels. If a nutrient level is below optimal the fertilizer recommendation, we’ll recommend more then is being removed by the crop. The idea is to build the soil test level up by applying more than is removed. Once the soil test is in the optimal range the recommendation will be to only apply maintenance or crop removal rates. This strategy works well on land that is owned or in a long term lease.

Another nutrient application strategy is the sufficiency approach. The goal of the sufficiency approach is to apply enough fertilizer to maximize yields in the year of application. This strategy may be appropriate for short-term lease farms. This approach requires annual applications of fertilizer, especially if soil test levels are below optimal. The lower the soil test level the more fertilizer is going to be needed in order to maximize yields. Some factors that will affect fertilizer rates required for optimal yield will be cropping history, soil type, nutrient placement and timing of application. Consult with your local MFA Agronomist to help fine tune nutrient applications.

With the drought and low yields this past year it is going to be tempting to reduce or eliminate fertilizer applications for the 2013 crop. I strongly recommend utilizing your soil test results to determine your nutrient application rates and not 2012 yields. If soil test levels are low, continue to apply recommended rates, you will be ahead of schedule and reach optimal levels sooner. If a nutrient is in the optimal or higher range then you can probably get by without applying a full rate or no fertilizer containing that nutrient.

Soil testing and interpretation is only a portion of a well developed nutrient management plan. A nutrient management plan should consider the 4R best management practices for each field. The 4R nutrient stewardship concept is to apply the right source of plant nutrients at the right rate, at the right time and in the right place. Visit with an MFA Agronomist to help develop a nutrient management plan that is tailored to your farm.

Steve Cromley is senior staff agronomist for MFA Incorporated. See related story about soil testing.

Ten scouting tips

Written by Dr. Jason Weirich on .

Scouting fields for weeds, disease and insects is one of the best investments you can make to maximize profits. We can expect to see more pests in our crops this year. The mild winter gives concern to the increased insect and weed pressure. I hope you consider evaluating every field in May—and I don’t mean the “windshield” scouting. Make sure evaluations are done thoroughly, it is a bottom-line consideration.

1.    Be proactive. A lot of information is available on the Web. It isn’t always the case, but you can often follow in-season situations occurring south of you and know these issues might be heading your way.

2.    Know the weather conditions. Mother nature can influence when weeds emerge, disease is present or insects arrive.

3.    Be thorough. The standard pattern for walking your field is a W. While you won’t walk every acre, this pattern will allow you to get a uniform sample from across your field. Be consistent in sampling methods. I like to see a sample point for every 2 to 4 acres.

4.    Keep good records. These records can help you make a prescription for your field. The notes will also help you make decisions next year. Before evaluating a field, know field history, cropping history, crop rotation, yield potential, pesticide application type, rate and history, variety/hybrid planted, planting date, planting rate, row width, tillage system, tillage timing, seed treatments, weather patterns, fertilizer and lime rates, previous pest problems, and other agronomic factors.

It’s time to fight resistant pigweed

Written by Dr. Jason Weirich on .

Residual herbicides should become a part of your weed-control

If you have attended a grower meeting recently, you have probably heard a lot about herbicide resistance—whether you wanted to or not. Herbicide resistance is not going away any time soon. As we move in to the growing season, we should all ask ourselves one question, “Do I want to be proactive or reactive?”

Since the introduction of Roundup-Ready crops in the mid- to late-1990s, glyphosate made weed control too easy. Farmers were able to plant crops, follow with one, or sometimes two, applications of glyphosate, and then they were finished.

In 2005, we started seeing and hearing about reduced control and weed escapes resulting in yield loss and reduced profit. Things got worse. And now, the days of efficient glyphosate-only weed control programs are gone.

If you don’t have glyphosate-resistant weeds yet and continue to use only glyphosate, it is a matter of time before resistance reaches your farm. And when that happens, residual herbicides will become a part of your weed-control program, if they aren’t already. Make sure to choose a residual herbicide that fits your weed spectrum. The MFA agronomy guide provides an excellent breakdown of each herbicide by weeds controlled.

Late fall tillage could mean big spring weed flush

Written by Dr. Paul Tracy on .

I know its February and weed control for the upcoming field season is probably the last thing on your mind. It is not uncommon to already have your plant food and seed inputs planned and purchased by now. Even though integrated pest management is reactionary by nature, planned pest management is often a very good idea.

Over the past several years, weed control systems have changed appreciably. Now is the perfect time to address those changes and prepare for the field season. Let’s discuss a few key components of a planned progressive weed control program.
Fall weed-control strategies have increased over the past decade. Many of these programs use residual products designed to keep weed pressure low through spring planting. We noticed a large downturn in fall herbicide use in 2010. The main reason given for less fall herbicide use was that the early harvest combined with dry weather allowed some much needed fall tillage to be done. Environmental conditions in 2008 and 2009 were not conducive to tillage.

As a result, many fields were severely rutted. Additionally, terrace work, grass waterway construction/maintenance, and drainage improvement projects, which were put on hold for several years, were finally initiated. All the ground work kept fall weeds in check. Don’t be lulled into a false sense of weed control security, as we often experience a weed flush following tillage. I expect to see that flush in full force this spring.

Be prepared to use an aggressive burndown program. In many cases, that burndown should include a full-rate residual product. If a residual is not used in the burndown, I recommend a planned residual as a preemerge or early post-emergent application.
Even with a residual herbicide, plan on an additional post application of glyphosate on tolerant crops once the weeds reach a height of 4 to 6 inches. Where resistance is an issue (almost everywhere in Missouri), the glyphosate needs to be applied with an appropriate tank-mix partner.

I am a big supporter of agronomy programs designed to slow weed, insect and disease resistance. I have discussed resistance as the key message in this column many times in my tenure. For obvious reasons, glyphosate resistance has received the most attention. However, as of 2010, the Weed Science Society of America lists 348 herbicide resistant weed biotypes present in over 50 countries. The United States alone accounts for 123 of those biotypes. To fine-tune those numbers, they represent 194 weed species and have been documented in over 400,000 fields.

Weeds developing resistance to glyphosate is part of a long list that includes resistance to seven other herbicide modes of action. In Missouri, 12 weed species have developed resistance to herbicides since 1992. They include common cocklebur, barnyardgrass, common sunflower, horseweed/marestail, common ragweed, Palmer amaranth, giant ragweed, annual bluegrass and most impressively, common waterhemp, which has developed resistance to four different herbicide families.

The society lists the following general principals of weed resistance management as:
•    Apply integrated pest management practices. Use multiple herbicide modes-of-action with overlapping weed spectrums in rotation, sequences or mixtures.
•    Use the full recommended herbicide rate and proper application timing for the hardest to control weed species present in the field.
•    Scout fields after herbicide application to ensure control.
•    Monitor site and clean equipment between sites.
For annual cropping situations they also suggest you consider the following:
•    Start with a clean field and control weeds early using a burndown treatment or tillage in combination with a preemergence residual herbicide as appropriate.
•    Use cultural practices such as cultivation and crop rotation where appropriate.
•    Use agronomic principles that enhance crop competitiveness.
Weed control strategies are constantly evolving. Even when the most aggressive herbicide programs are required, the return on investment is very positive, especially with today’s commodity values. Don’t let the season sneak up on you. Take time during a cold February day to visit with your local MFA Certified Crop Adviser. They can help develop a custom weed control program for each of your fields.
Dr. Paul Tracy is director of agronomy for MFA Incorporated.


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