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Features Agronomy
Hidden key to IPM? Effective nutrient management


March 10, 2014
By Mike Jiggens


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Effective nutrient management is the hidden key to integrated pest management, a research agronomist with Koch Fertilizer, told an audience of golf superintendents in December at the 25th annual Ontario Seed Company/Nutrite professional turfgrass seminar in Waterloo.

“Healthy turfgrass minimizes the need for plant protection chemical inputs, and healthy turfgrass depends on an effective nutrient management program,” said Dr. John Kruse.

Koch Fertilizer, one of the world’s largest nitrogen fertilizer makers, is a subsidiary of Kansas-based Koch Industries, which also has interests in cattle, petroleum, and pulp and paper.

Kruse said that soil fertility doesn’t immediately come to mind when thinking about IPM, but noted that to achieve overall healthy turf, the need to use materials to bring a turfgrass system back from a constantly sick system is going to be reduced.

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An effective nutrient management program factors in the need for highly-efficient methods for nutrient delivery and the need to know a soil’s conditions, he said.

Kruse offered a brief history lesson to explain the advent of nitrogen in fertility. About a century ago, a couple of German researchers took nitrogen from the air—the only place it was available in abundance (making up about 78 per cent of the air we breathe)—and discovered a means to break apart the atom’s triple bond. The nitrogen was put under tremendous pressure and the heat elevated to about 1,000 degrees Fahrenheit. A catalyst was thrown in and was combined with hydrogen from natural gas to come up with ammonium.

From that point on, Kruse said, our diets changed dramatically because sufficient nitrogen could be manufactured to grow enough crops for raising animals in large numbers.

Although the nitrogen which is abundant in nature is inert, that which is taken up by plants is in the form of ammonium and nitrate.

“We apply fertilizer in order to apply nitrogen in those forms that plants can take up as plant food.”

The most common form of nitrogen applied in the turfgrass industry is urea. There are transformations which occur when urea is applied.

Ammonium and nitrate are, respectively, positively and negatively charged. Most soils have a net negative charge. Like a magnet, in which the positive and negative poles attract and “click” together, the same happens with ammonium in the soil. It’s clicking on the cation exchange capacity found in the soil whereas nitrate, with its negative charge, doesn’t want to stick anywhere in the soil, such as what happens when two like poles of a magnet repel one another.

When water moves along, nitrate has nothing to hold onto and can leach through the system.

Kruse said it’s important to understand this to be able to increase the efficiency of fertilizer.

In the soil solution, there is both ammonium and nitrate. The ammonium tends to stick on a cation exchange capacity typically found on soil organic matter and on charged clay particles in the soil. Nitrate, on the other hand, moves in the pool water. When the root wants to take up the nutrient, it must go through a process. There is a charge, and a plant must maintain an electrical neutrality. If the plant takes in ammonium, it has to pass through a barrier which regulates this chemistry in the plant—its Casparian strip. The ammoniun which passes through the Casparian strip forces the plant to do something about the extra positive charge. Typically, it will release a hydrogen ion because it also has a positive charge.

“That’s one of the reasons why in a root zone in the rhyzosphere immediately around the root, you’ll find the pH is typically a little bit lower than the surrounding soil because the plant is constantly releasing some hydrogen ions.”

Before the advent of fertilizers, grass still existed and grew but was getting its nitrogen from plant residues and converting it into soil organic matter. As microbes broke down the soil organic matter, it converted it into plant food which was ammonium. Science copied that by applying fertilizer typically as a urea which is broken down by an enzyme called urease and converted into ammonium.

“So we’re actually supplementing Mother Nature with our fertilizer.”

But nature is still not yet finished with the ammonium, Kruse said. Microbes in the soil, such as nitrosomonas, will utilize the ammonium, and it has an enzyme which will break ammonium and convert it into nitrite, ultimately to be converted into nitrate.
He said this is where there may be potential environmental problems because the nitrite can either be broken down again and turned into nitrogen gas or nitrous oxide, or it can leach out through the bottom. The conversion into nitrogen gas or nitrous oxide is nature’s way of completing the nitrogen cycle, he added, noting nitrogen is taken from the air, converted to fertilizer, becomes plant food in the soil, and then eventually becomes nitrogen gas.

The problem for superintendents, Kruse said, is that some of the nitrogen might be lost to the environment, and they will have to deal with the consequences.

When urea is applied to a turfgrass soil environment, it dissolves with a little bit of moisture and is on the surface. The urease enzyme is found in the plant tissue and in the soil, and its only job is to break apart urea. As it does, one of two things will happen: it will go off as ammonia gas or will convert into ammonium plant food.

Kruse said the question to be asked is to determine who much is going off as gas and being lost to the environment because there is a concern about the cost and the desire to keep as much as possible as plant food.

The urea molecule is consuming hydrogen by borrowing it from the soil. While doing so, the pH is going up.

“You’re in this equalibrium between ammonium and ammonia.”

The pH is going up and, when it reaches 9, about 50 per cent of the nitrogen is converted into ammonia and goes off as gas.
If urea is surface broadcasted and isn’t watered in deeply, in a few days about 40 per cent of the nitrogen is lost.

On a golf green or a sandy soil situation, there are microbes in the soil converting the ammonium into nitrate and, when irrigated or after a rain event, the water pushes the nitrate through the profile because it’s not sticking to the soil.

As soon as the fertilizer is below the root zone, it’s lost and becomes an environmental situation, “so we need to minimize leaching as much as possible.”

On the flip side of that, with heavier soils, a heavy rain will produce water which stands there and ponds. Microbes which are breathing and consuming oxygen in the soil don’t simply drown if they run out of oxygen due to a cap of water. Kruse said they “flip an internal switch” and start to consume oxgen from nitrate.

“When it suits them, they can go anaerobic and can start breathing the oxygen out of the nitrate.”

Turfgrass managers have recognized that not only can they burn turfgrass if excessive amounts of urea are applied, but that the colour doesn’t last particularly long if they are applying only raw urea. Thus, they have been utilizing enhanced efficiency fertilizer technologies.

“Sometimes we overlook the mechanism there—why they work, the way they work—and maybe all the categories that are available to you as tools.”

In the 1950s, the Tennessee Valley Authority took molten sulfur with coated urea, and it was the first practical way in which controlled-release fertilizer was created. It relied on micro fissures and then finally cracked open. Water penetrated the micro fissures, breaking it open and releasing the urea.

Polyurethane-coated fertilizers work a little differently. The polyurethane is a plastic which allows an osmotic effect to occur so that water penetrates through the polyurethane lining, dissolves the urea which creates a lot of pressure, and the urea solution oozes out of the prill.

“Once it’s outside the prill, it’s urea again.”

With stabilized nitrogen, it’s not necessarily doing anything directly to the fertilizer itself, Kruse said, but is rather affecting the enzymes in the soil, making it neither a slow nor controlled-released fertilizer. It affects enzymes, but the result is it allows for an extended amount of feeding by keeping the nitrogen in the soil in a form which doesn’t just wash away.

The health of turfgrass is affected by pH.

“It can dramatically affect the rooting depth and it can affect the nutrient uptake and therefore the overall plant health.”
Kruse said imbalances in pH force turf to always be on the verge of sickness, resulting in turf managers typically overcompensating with more fertilizer than usual. Some pH issues can be corrected and some are so tough they must be managed around. The pH is a measure of the amount of hydrogen in the soil. For most turfgrass sites in North America, pH runs between 4.5 and 8.5 with 7 considered neutral.

Simply adding lime doesn’t automatically change something in a dramatic and immediate way, Kruse said. It takes time and sometimes different rates. The ability to resist change is what’s known as “the buffer effect.” Where a lot of the exchange capacity or buffer capacity in the soil is found in the clay or humis.

With the buffer effect, it’s possible to have two different soils with two different textures that start out at the same pH and the same amount of lime is added. One soil is sandy with a pH of 5.5, a ton of lime per acre is added, and six months later the pH has risen to 7.0. Another soil in Canada also has a pH of 5.5 and a large buffer capacity. A ton of lime is added, and six months later the pH has increased to only 6.1. The richer, heavier soil had more buffer capacity and didn’t allow the pH to climb as much.
“That’s why it’s so critical to take those regular soil tests and find out where you are in the system.”

Kruse said another important point to realize is that soil acidity is much more than just hydrogen. What really causes problems is aluminum, he said, which tears up and destroys the dividing tissue at the root tips and breaks it apart and stops it from being able to divide.
“As you increase the amount of free aluminum in the soil, your root systems dramatically decrease.”

It’s important to explore ways to decrease the amount of free aluminum in the soil, he suggested. The optimal range for pH is between 6 and 7 which not only prevents aluminum toxicity from happening but ensures maximum fertilizer usage.

When a fertilizer based on ammonium is applied, whether it’s urea or ammonium sulfate or something similar, the ammonium in the soil’s conversion to nitrate releases hydrogen.

“A little bit of fertilizer can create quite a bit of hydrogen and that changes your pH and makes it much more acid.”

Kruse said that is why pH can be a moving target as a counter balance is needed when applying nitrogen fertilizer. When applying nitrogen fertilizer, especially urea, an initial spike in pH from hydrolysis can be realized but then, with the conversion of ammonium to nitrate, the pH comes back down yet at a lower level.

“So you can get these wild swings in pH around a nitrogen fertilizer application.”

The wild swings, he said, are addressed by enhanced efficiency technologies such as stabilized nitrogen which helps prevent rapid spikes.

Coated fertilizer gives the same effect because it’s releasing only a little bit of urea at a time.

“It’s not overwhelming the soil and it’s not suddenly consuming all that hydrogen.”

A lower spike in pH is realized with a coated or reacted fertilizer, Kruse said, adding they’re accomplishing the same things, but are doing them in a different way.

Lime isn’t very soluble and it takes a tremendous amount of water to move it. The best time for incorporating lime is when first building a golf course, he suggested.

Limestone is calcium carbonate and, when it dissolves in water to get calcium and carbonate, the carbonate reacts with the hydrogen to create CO2 and water. It’s a complete chemical reaction, consuming all the hydrogen and allowing the pH to go up.
One pound of nitrogen per 1,000 square feet is about the same as 95 pounds of urea per acre. It takes about 175 pounds of limestone to neutralize the acidifying effect of 95 pounds of urea per acre.

Phosphorus can get bound up in a high pH soil. If seeding in a high pH soil, attention will have to be made to that, Kruse said, because a lot of micronutrients become far less available once pH goes up. He suggested it might be better to apply micronutrients as a foliar.

The real problem with an acid soil is not so much the hydrogen, but the damage being caused by the free aluminum. Adding gypsum, or calcium sulfate, won’t change the pH of the soil but will react with the aluminum and precipitate it out so that it’s no longer toxic to the roots.

Water salinity

The same audience of golf superintendents also heard from Dr. Ron Duncan of Florida-based Turf Ecosystems, who spoke about “an ecosystem management approach, including IPM, to soil and water salinity challenges.”

Just because a golf course uses potable water for irrigation purposes doesn’t make it potentially problematic, he said.
“You see the disease issues very quickly, but you don’t see the salinity buildup, salinity accumulation issues that come from irrigation watet to arrive overnight. It takes months and years.”

Several courses which have hired his consulting services had been using potable water for irrigation purposes and experienced no problems for decades, and then they suddenly began to lose grass. By then, the superintendent is already in trouble.

“It’s kind of a reality check when I have to look at the general manager and the owner of the facility and tell them this is going to take five years to fix.”

It will also take significant money to turn things around, Duncan added.

Superintendents are equipped with more tools than ever to help with monitoring their water. He suggested irrigation water be analyzed in a lab to assess its quality and makeup.

“Don’t assume that five years down the road that you’re still going to be OK because you may not.”

Duncan asked his audience if they had been seeing more incidents of localized dry spot. Those who had should know there is a direct relationship with an increased accumulation of salts, including high sodium, high bicarbonates and high total salts, he added.

It’s not the primary cause of LDS, he noted, but it is an escalating part of it which is starting to show up more frequently.
Kentucky bluegrass has a low salinity tolerance in general, and is one of the first species to suffer from a salinity standpoint. The imbalance of nutritional availability for the bluegrass to pull it up causes it to turn yellow.

In high-traffic areas, salinity issues are enhanced when there is accumulation over time.

“Salts have an uncanny ability to migrate to certain areas and build up and stay and continue to build up in that area, and they’ll leave the other area alone.”

One part of a green may be perfect, but grass is being lost at a spot only a metre away.

Duncan said the industry is starting to understand more of the subsoil migration of salts over time with gravity and rainfall. Its impact on the root system is the biggest problem as nutrient and water uptake is compromised. Disease then sets in, and that’s when superintendents tend to respond.

Regrassing a damaged area due to salt-induced disease is simply putting a band-aid on the problem without fixing it, he said.
If a golf course has saline-stressed turf, it will likely see more disease down the road, causing an increase in fungicide expenses.
“We’re still on a learning curve and will be for a while,” Duncan said, but added much more is understood today than it was even five years ago.

Attention has turned of late to a closer look at the microbial aspects. He said he is concerned that as salinity builds up in the soil profile that it might negatively affect the good microbes which help break down fertilizers essential for the plant to take up.
Duncan urged his audience to get their water and salinity levels tested.