Fine-tune in-season nitrogen

Written by Jason Worthington on .

In-season nitrogen applications on corn and wheat have long been a part of Midwestern fertility programs. It is rare that wheat fields don’t receive a topdress application of nitrogen—if not two spring applications.

In-season topdressed nitrogen in corn is increasingly common whether it comes as a planned application or as a rescue application.

The perennial question that growers and applicators ask prior to the in-season topdress is how much nitrogen should be applied. That, of course, is the million-dollar question. If you answer it right, you get maximum yield for the input cost. If you answer it wrong, you either leave yield on the table or waste inputs.

Applying the right amount of in-season nitrogen is going to depend on a multitude of factors including soil organic matter; amount of nitrogen applied pre-plant; amount of nitrogen mineralization in the given year; yield potential of the crop; amount of nitrogen leached; amount of nitrogen denitrified; the previous crop, nitrogen stabilizers used, and more. You can see from that list of variables that the right topdress rate of nitrogen won’t be the same every year. Beyond season-to-season variability, changes in topography and soil type within the same field means the appropriate rate will not necessarily be the same from one end of the field to other.

We now have decades of experience in variable-rate fertilizer application. Through this experience and fine-tuning our abilities to collect yield data and soil test information, we have created very accurate recommendations for nutrients like phosphorus and potassium. Building an accurate variable-rate nitrogen recommendation has been more elusive. Improvements on variable-rate nitrogen are hitting the marketplace, however. Choices growers have right now basically come from one of three categories: machine-mounted crop sensors, aerial imagery or nitrogen models.

Crop sensors

Of variable-rate topdress options available, first to the market were crop sensors mounted to nitrogen application equipment. These on-the-go systems, such as AgLeader’s OptRx, work by reading near-infrared light reflected off of target plants. Dark green plants with sufficient nitrogen absorb more and reflect less light than lighter green plants that need more nitrogen.

For variable-rate topdressing with these systems, the first step is to measure areas of sufficient nitrogen and deficient nitrogen in the field with the sensors by driving over the field.

Once initial measurements are taken and application begins, the sensors continuously read the amount of light reflected. Application rates are calculated and adjusted on the fly by the computer and variable-rate controller on the machine. This process is very convenient due to the fact the applicator doesn’t need a recommendation built beforehand. The recommendation is built on the spot by the need of the plants. On the other hand, that means you won’t know how much nitrogen product is required until after application is completed, which can lead to challenges with product delivery.

Aerial imagery

Using aerial images to determine a variable-rate nitrogen recommendation on a field is similar to the principle behind on-the-go sensors. In this approach, the reflectivity of target plants is acquired by an aerial image to determine the topdress nitrogen rates throughout the field. The information can be measured in several different spectrums, but the theory is the same—crops with adequate nitrogen will be greener than those with inadequate nitrogen. The major difference between aerial and on-the-go measurements is that the aerial images can be turned into nitrogen recommendations before the applicator heads to the field, so the total amount of nitrogen is already known.

MFA is evaluating software that processes high-quality images captured from satellites, airplanes or even a grower’s drone to create in-season nitrogen recommendations. The processing time involved in building the recommendation is the challenge. Timing becomes an issue as well. Aerial images and crop sensors work best when the crop canopy is closed, which ensures reflected light is coming from leaves, not bare soil.

Nitrogen models

Nitrogen models work much differently than sensing technologies. Instead of taking a light reading to determine the nitrogen sufficiency of the crop at a specific point in time, nitrogen models attempt to measure the factors that affect nitrogen availability, loss, and a crop’s yield potential to create a nitrogen recommendation. The variables listed above are entered into the model or measured throughout the season to figure nitrogen loss and mineralization. The model’s goal is to predict nitrogen needs for the remainder of the season. This is advantageous from the standpoint that recommendations can be made with some added accuracy over typical flat-rate recommendations. However, if any information is left out or unaccounted for the accuracy of the nitrogen model will decrease. Where sensing or imaging technologies measure current conditions, models are working off of a lot of calculations and assumptions.

Regardless of the method used to develop more accurate in-season nitrogen recommendations, these new options should excite growers. The goal of variable-rate technology with nitrogen and other nutrients is to make sure the right rate is applied in the right place. This is good stewardship for the environment and leads to increases in agronomic productivity and cost efficiency of your inputs.

Keep tight reins on crop nutrients

Written by Dr. Jason Weirich on .

Nutrient management is a leading topic for farmers and ag retailers. It’s going to stay that way for a while. If you look at what’s going for agricultural industry, you see increasing restrictions and requirements on fertilizer manufacturers and suppliers. If you look at the farm level, you see increasing scrutiny on how we use commercial fertilizers.

A 2012 a study from Purdue found that 40.5 percent of row-crop expenditures were spent on fertilizer. That’s a major part of a crop-year investment. Clearly, to be a good manager fiscally, environmentally and agronomically, you need to prevent as much fertilizer loss as possible.

MFA’s Nutri-Track bases recommendations on soil test and yield removal. The program allows you to apply variable-rate N, P and K based on your yield goals and measured fertility levels across the field. Nutri-Track focuses on putting nutrients where they are needed and avoiding over-application in areas that won’t perform.

While some growers assume this kind of management will reduce overall fertilizer application rates, that’s not the case most of the time.

Yield is never even across a field. But what is the variability in nutrient removal from your fields? We know that corn uses 0.45 pounds of P and 0.25 pounds of K per bushel grain produced. Soybeans use 0.9 pounds of P and 1.5 pounds of K per bushel.

How much difference does it make?

Try this example. You have a corn field that has a 150-bushel-per-acre average yield, but varies throughout the field from 80 to 190 bushels per acre.

If you made nutrient plans on a flat 150-bushel-per-acre removal rate, the areas that yielded 80 bushels per acre would receive an extra 31 pounds of P and 17 pounds of K. The areas that yielded 190 bushels would be short 18 pounds of P and 10 pounds of K.

Or, you have a soybean field with an overall 50-bushel-per-acre average but a range of 20 to 80 bushels per acre. If you use the flat 50-bushels-per-acre removal rate, the parts of the field that yielded 20 bushels would receive an extra 27 pounds of P and 45 pounds of K. Areas that yielded 80 bushels would be short 27 pounds of P and 45 pounds of K.

The trick is getting nutrients in the right place at the right time and in the right amounts.

Keep that nitrogen

The other aspect of making sure we are good stewards of our nutrients is stabilization nitrogen. Most recently, I’ve written about the importance of protecting nitrogen from volatilization losses. However, there other modes of loss. Let’s focus on denitrifiction and leaching.

Ammonium (NH4+) sources in the soil go through a process called nitrification. Ammonium is converted to nitrite (NO2-) by nitrosomonas bacteria, and nitrite is further oxidized to nitrate (NO3-) by nitrobacter bacteria. A majority of the nitrogen taken up by the plant is in the nitrate form, however most plants can also take up ammonium (NH4+). Once in the nitrate (NO3-) form, the nitrogen is subject to leaching and denitrification losses. Nitrate moves freely throughout the soil profile with moisture. In coarse-textured, well-drained soils nitrate can leach below the root zone where they become unavailable to the crop. Nitrate is also subject to denitrification losses. Denitrification is a biological process that converts nitrate to gaseous forms of nitrogen that are lost to the atmosphere. It occurs in soils that become waterlogged.

Currently there are two proven nitrification inhibitors on the market: nitrapyrin and dicyandiamide. Nitrapyrin has been used since the 1960s. It has long been marketed as N-Serve and most recently as Instinct, an encapsulated product for dry and liquid fertilizers. Instinct can also be used in liquid manure. The other proven nitrification inhibitor on the market is dicyandiamide (DCD). DCD is the nitrification inhibitor in Agrotain Plus and Super U.

Growers often ask me just how long N-Serve protects nitrogen in the soil. A general rule of thumb is 90 days for fall-applied nitrogen. Keep track of those days by counting application until soil temperatures drop below 40º F. Resume counting in spring when soil temperatures warm above 40º F.

For spring nitrogen application, expect 8 weeks of activity from an April 15 application; 7 weeks from a May 1 application and 6 weeks from a May 15 application.

Research indicates about a 7 percent yield advantage from fall-applied and a 5 percent advantage from spring-applied nitrogen.

Not a complete wash

Written by Dr. Jason Weirich on .

I would love to deliver this column with the message that we harvested a bountiful crop at our research site last year. Instead, I have to tell you that our research and training plots got a taste of the same weather challenges and environmental damage that other producers in MFA’s trade territory endured in 2015.

This past year was one for the record books. Our planting crew got the corn in the ground in good shape on April 22. Everything seemed like it was going to be perfect. But we had a lot of moisture at the wrong times.

Over the past few years at our plot location near Boonville, Mo., we’ve had some trouble with lodging. In light of that, we made the decision to delay planting our soybean crop until later in May—even though weather would have allowed us to get it in the ground earlier. You can guess what’s next. Soybean planting at the location went from the planned May target date to planting on June 7. Following planting, the skies stayed dark and full of rain. Beans tried to emerge through standing water. Needless to say, our planting-date study turned into a two-date planting-date study—one on June 7 and one on July 6. Surprisingly, the late-planted soybeans caught up to the early-planted soybeans’ height.

Once the crops were in and up, we had MFA employee training on July 29 and a two-day producer tour on August 6 and 7. About 800 people attend these events to learn about different production practices and new products coming down the pipeline.

If you were able to attend either one, you will recall that the corn was outstanding. I only wish it would have finished that way. On Sept. 10, a severe windstorm blew through the area. It caused severe lodging in our corn plots. Flattened corn, with stalks jumping across plot lines is not a pretty sight for a researcher.

We were able to harvest one of the early-look variety trials by having two people on each side of the combine to make sure we didn’t have any contamination from any of the other hybrids. But as we progressed, the practice looked to be less than safe. Thus, we decided to let our plot cooperator combine the rest of the corn. It would have been great to see results from our studies on nitrogen timing; nitrogen source; phosphorus enhancement products; foliar fertilizer; fungicide timing; and variety trials. But employee safety was top priority.

While the corn ended up flat on the ground, we were very hopeful that the soybeans would continue to stand. Although we had severe water logging and stand issues from the rain earlier in the season, we ended up with several good trials. This was the first year we were able to harvest all of the soybean plots at training camp.

We have been testing biologicals from Monsanto Bio-Ag the past couple years and have reported excellent results. Some of the other trials we have been conducting include seed treatments, seed nutritionals, tank contamination, phosphorus enhancement products, Aspire with Microessentials, and varieties to name a few. While they are not reported here, they will become available.

Although last year wasn’t the year we wanted from a research standpoint, we did the best we could. We join you in looking forward to a better growing season this year.

CLICK HERE for more in the Feb 2016 Issue of Today's Farmer Magazine

Drive and learn

Written by Dr. Jason Weirich on .

One thing you can’t complain about as a farmer is the view. Whether it’s the sun setting over a freshly cut hay meadow or watching a whitetail buck dart across a field when he is spooked from a resting spot, there is a lot of beauty in the rural setting. We can debate just what kind of country scene is the most enjoyable, but I’ll suggest that of all the views on your farm, there is one that provides more useful information than most: the one from your combine cab.

What you see from the combine cab can tell you a lot about the cropping year, the success of your management practices and the success of the products you have used. How you’ve done with weed control, planter setup, and water management decisions are just a few things that you can really verify by paying attention to what your field at harvest is telling you.

Here are some tips for a successful combine ride.

Don’t devote 100 percent of your attention to your yield monitor

It can be easy to jump to conclusions if you are not focusing on the right things. For example, yield monitors are great, but often they become such a strong focal point in the cab that they blind you to other information that can provide real insight. The yield data that can be compiled and used for nutrient-removal recommendations along with other long-term trends is very valuable if looked at objectively. Watching the swings on the monitor from the cab can lead to rash decisions. Make sure your monitor is logging information so it can be analyzed later. Then dim the screen for a couple rounds so you can focus on what’s going on in the field.

Grade your planting job

One of the best ways to do this is to evaluate the consistency of corn ears as they enter the head. Not just consistency from one area of the field to the other, but consistency from one ear to the next. Ideally, every ear would be the same size, but fluctuations in timing of emergence or fluctuations of intra-row spacing can really influence ear-size consistency. After ear consistency, evaluate stalk consistency both in spacing from neighboring stalks and in size compared to neighboring stalks. The cause of a spindly stalk is sometimes obvious from the cab. If spacing is even, the plant probably emerged late. If spacing is uneven, intra-row competition is often to blame.

Grade your weed control

Evaluating how weedy a field is from the cab is a universal practice. But to say, “Boy, that field is a mess!” or, “Man, that field is clean!” is not enough. Try to note not just how severe the weed pressure is, but also how diverse it is. What weed species are present? Paying attention to weed height might give some clues about when they emerged. Also, look at the crop condition around the weeds. Was it late pressure due to a delayed or inadequate crop canopy, or is there something to evaluate in the timing or product selection of the herbicide program?

Look for causes, not just effects

There are hundreds of issues both positive and negative that can be picked up from the cab. There are thousands of variables that may have caused that issue. If there is lodged corn, get out and split some stalks. Are there tunnels from insects? Is stalk rot present? Is this a wet area of the field or a droughty area? Is the soil type the reason for a change in performance, or is the nutrient level? Very often the view from the combine will answer questions. It can also raise more questions. But raising those additional questions can still be a valuable part of finding the right answers to improve your stands and yield.

Take Notes

Finally, what I’ve mentioned above is the kind of information you use when you sit down to discuss a crop plan with your MFA advisor. Write it down so you can have it with you. When you bring your MFA precision representative yield data to analyze the notes you take from the field, these extra notes may be the key to really unlocking the information on that field.

Of all the points in the year, harvest can be one of the most enjoyable. However, to ensure that there are future, better harvests to enjoy, it’s best to take the information your field has to offer and make improvements on the lessons these fields provide. Those lessons and improvements must come from objective observations. Informed decisions are a best management practice!

Damaged hay may short your herd

Written by Dr. Jim White on .

The weather challenges from 2015 continue to present themselves. As I write this, available forage is on the wane due to dry conditions. For many producers, it’s time to feed hay. And much of that hay might be of low quality because, in the early summer monsoons, it was rained on before it got baled.

There are no robust guidelines that can accurately estimate the amount of damage or the actual feeding value. The factors influencing rain damage are just too variable. They include the amount of rain that fell on the hay and how long it rained. How dry the hay was before the rain has an effect, as does the drying conditions after the rain. How the hay got raked between the rain and baling, moisture of hay when baled and quality of hay when cut are also factors. Mold is common in rained-on hay. Often the hay was baled too wet, either to avoid further rain damage or to remove it from the field to reduce its impact on regrowth. But even when the bales are ready and waiting, feeding moldy hay to livestock is a tough decision.

All hay contains some mold, but when mold becomes easily noticeable, feeding management becomes more important.

Usually, mold makes hay less palatable, which can result in lower intake or even in animals refusing to eat the hay. Other problems from mold can occur due to mycotoxins produced by certain mold fungi. This also is part of the decision process, since not all molds produce mycotoxins. When they do produce mycotoxins, it’s hard to predict how much they will produce. The good news is, mycotoxins rarely are present in hay unless it has mature seeds.

Laboratory analyses for molds and mycotoxins are available, but are relatively expensive. Often, each mycotoxin must be measured individually. That increases the cost, and if you aren’t testing for the right mycotoxin, can give you an incomplete picture. Moreover, the test is based on the sample hay sample you send in, which may or may not be representative of the larger hay supply. Mycotoxin concentration usually is highly variable.

Direct negative effects of moldy hay are difficult to document. Horses may be the most sensitive to mold among common livestock. For example, mold spores often contribute to respiratory and digestive problems like colic or heaves in horses.

The best course of action is to minimize feeding moldy hay to more sensitive animals, like horses or pregnant cows. This may require a keen eye or sensitive nose when selecting hay to feed each day.

Mixing moldy hay with other feedstuffs can dilute mold problems, but be careful that you don’t make your animals sick by tricking them into eating bad hay that they normally would refuse.

Hay baled too wet is susceptible to heat damage, also called enzymatic browning. It is caused by heat produced by microorganisms in the hay as they use plant sugars and oxygen. If enough heat is produced to raise hay temperature above 125 degrees, chemical reactions occur that combine amino acids from protein with sugar to produce compounds similar to lignin.

These heat-damaged protein compounds are poorly digested but often smell sweet like caramel. You may see hay turn a tobacco-brown color. This damage sometimes produces flavors that cattle find exceptionally palatable.

Although livestock may favorably consume heat-damaged hay, the protein value they get from it can be unexpectedly low. Standard forage tests can predict energy available from heat-damaged hay, but the standard crude protein test cannot distinguish between usable crude protein and heat-damaged protein. Thus, standard tests may significantly overestimate the usable protein in the forage.

The lab test used to measure heat-damaged protein, which can then be adjusted to account for the digestibility/availability of the feed protein, is the acid detergent insoluble nitrogen (ADIN) test. It is also known as acid detergent fiber crude protein (ADF-CP) or insoluble crude protein (ICP). When heat damage is suspected, ask your lab to conduct this test and adjust crude protein accordingly.

Rain damages hay in several ways. It leaches soluble carbohydrates, proteins and minerals out of the hay. Leaves are lost. Extended drying time reduces carbohydrates due to plant respiration and microbial activity.

Three primary factors are involved in dry matter losses—leaching, respiration and leaf loss. Leaching is the movement of cell solubles out of the plant. Components of the plant that are very water soluble are leached out of the forage and lost when rained on. Basically, if a nutrient is highly digestible, it is also prone to leaching losses. About half of the dry matter leached by rain is soluble carbohydrates.

Most often, fiber concentration increases and crude protein concentration remains about the same after hay has been rained on. Digestibility and energy usually decline. The increase in fiber concentration is due to soluble carbohydrates and other components leaching from the hay—fiber isn’t actually increasing.

The digestibility of rain-damaged hay will be reduced. Many factors contribute to this: leaf loss, soluble carbohydrate leaching, the increased levels of fiber and ash by concentration. Forage digestibility may be reduced by just a little or up to a third.

The amount of change in nutrient concentration is highly unpredictable. If you are counting on hay that has been rained on or put up wet, a laboratory analysis for nutrient content will help you adjust the supplements you need to keep your livestock in condition



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