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Growing crops means managing complex ecology

Jan. 10, 2013 | 0 comments



Farmers might think of their work as simple, but looked at more closely it's really a complicated affair.

Simply to grow corn is to manage a number of factors - each of which can determine the success of the crop. These interacting factors determine nutrient availability and plant health.

"You're managing a very dynamic system - an ecology - when you're running a farm," says Dr. Don Huber, emeritus professor of plant pathology from Purdue University.

His research over a more than 55-year career has focused on the epidemiology and control of soil-borne plant pathogens with emphasis on microbial ecology, cultural and biological controls and physiology of host-parasite relationships.

"This is a miraculous factory you're running. Plants store the sun's energy as sugar, so the harvest is sugar and protein."

Understanding this "ecology" of crop production means understanding the abiotic environment (things like moisture, nutrients, temperature, pH, ag chemicals) pathogens, plants and their development and the biotic environment (things like antagonizers, oxidizers and mineralizers.)

Often plant nutrition and the availability of nutrients can be the key to resisting specific pests. For example, Huber showed pictures of a wheat field that had small spots with diseased wheat plants scattered among the healthy ones.

It turned out that dairy manure spread in the field had created small pockets of excess nitrogen, which had immobilized the manganese in those spots, so it was unavailable for the wheat plants and caused them to lose their resistance to a specific plant pest.

Huber was a featured speaker at the "Farm to Plate" seminar Jan. 3-4 in Wisconsin Dells, sponsored by FHR of Stewartville, MN, a nutrient management company "by growers for growers."

Huber told the farmers at his session that plants have "tremendous yield potential" and farmers are perhaps harvesting only 25-30 percent of this genetic potential. "What we harvest is what's left over after all the stresses and they all have a relationship to nutrition.

"We're interested in a balance relative to the needs of the crop. Often the problem is a problem with the roots."

Nutrient balance is important because each element functions as a part of a delicately balanced, interdependent system with the plant's genetics and the environment. Nutrient balance, says Huber, may be a matter of disease or root function.

"The weak link may be underground - the root of the problem may be the root."

Plant breeders may not start with the root of the plant, but sooner or later they generally come around to the idea that good roots can scavenge more nutrients from the soil and therefore are of critical importance, and then they begin to work on that, Huber said.



BETTER ROOTS

In addition, better roots can be a way to create better soils, he maintains, because if the plants have a better root system it can lead to more sustainable practices and the potential to reduce inputs by as much as 20-40 percent. Those things will help improve profits as well.

Farmers (and gardeners) often wonder how weeds can prosper and look healthy when the crops around them are withering.

Huber said the reason might well be underground in the health and capacity of their roots. Many weeds are able to go deeper than crops and scavenge minerals to keep them healthy.

The deep soil layers are a "lost treasury" of minerals. In addition weeds may be three to four times better at taking up certain micronutrients than are our crops.

Micronutrients in the soil are components of the soil that are regulators, activators and inhibitors of physical processes.

Manganese is responsible and necessary for water splitting and its availability is critical for certain plants to resist disease. Magnesium is part the chloroplast, necessary for photo synthesis.

They are two of the 17 or so elements that a plant needs for proper development.

Crops differ in their ability to deal with low levels of various essential minerals and many forms exist for each essential mineral. Some plant species or even cultivars can use forms that are not available to others.

"There is a tremendous range in nutrient efficiencies in different varieties."

Some rye varieties have been bred for manganese efficiency.

He also noted that the crop that was grown on a field in a previous crop year can help or hinder with the availability of certain micronutrients like boron, copper, manganese and zinc.

Again Huber stressed the importance of the root system in taking up these nutrients. "Early corn has a more fibrous root system but later corn has less fibrous roots that go deeper and make those plants more drought tolerant. You are managing that ecology by some fairly simple things you're doing."

The difference of five-six degrees can mean a huge difference in root structure and configuration. "Why does the root stop growing? It could be disease, compaction, low oxygen or drought but sometimes its just low boron or manganese. Nutrient absorption is very important in the process."



MIGHTY in FUNCTION

Though micronutrients are small in quantity they are mighty in function and a deficiency in one of them, like boron, cobalt, copper, iron, manganese, molybdenum, nickel or zinc, can stop everything downstream from them or reduce its efficiency, he said.

Having talked about how important these micronutrients are, Huber talked about how some crop protection chemicals can alter the availability of these elements by chelation.

All herbicides and pesticides, he said, are nutrient chelators, meaning they grab hold of a nutrient and change its availability. Some are used to immobilize certain micronutrients and shut down certain nutrient systems or enzyme pathways as a way to kill weeds.

He showed a complex pathway for creation of cell walls and how the chemical glyphosate (Roundup) changes that pathway as a broad spectrum chelator.

One of the challenges for growers is that deficiency symptoms for various micronutrients are frustratingly similar to each other. Many include stunting, yellowing, slow growth and small leaves. Multiple deficiencies can confound remediation responses too, he added.

Sometimes Huber is asked to figure out what could be the problem in a variety of fields. He was called out by an Idaho Potato Commission grower to try to solve the mystery of why potatoes died two weeks earlier than ever before. He determined that use of glyphosate-resistant corn in the previous year's crop had changed the biology of the soil environment and cut the availability of manganese for the potatoes.

Huber agrees with fellow researchers that crops can be suffering moderate to severe deficiencies of these micronutrients and not see any symptoms on the plants.

Some of these deficiencies have come by way of "improvements" in fertilizer technology. He talked about nickel deficiency in pecans and soybeans because of cleaner fertilizers.

"We used to get a pinch of it in as a contaminant," he noted.



NUTRIENT AVAILABILITY

The reasons nutrients are not there for crops to use can be many. They may not be present in the soil or if they are there, they may not be available for plants to take up, based on their form or solubility.

There may also be soil conditions that prevent the uptake of nutrients like the wrong pH or compaction or the wrong temperature. Plant health could be another reason that these nutrients can't get taken up.

Management practices like the use of glyphosate and no-till can tie up nutrients, he said. In the case of no-till practices there is little mixing or recycling of the soil as there would be in plowing.

Huber says that changing one thing, like using glyphosate-resistant corn, changes a tremendous number of things in the field ecology.

He believes that the new crop technologies, including widespread use of glyphosate, is affecting micronutrients levels in the soil. "We're seeing manganese deficiency levels at ranges where we were formerly sufficient."

He also highlighted some iron-deficiency research related to the use of glyphosate.

Farmers need to look at the dynamics of the ecological system they are farming and managing and try to enhance the ability of the plants to work for them.

"It's not an exact science because it's dynamic, it's an ecology."

The objective of growing crops is to move conditions apart that bring disease and bring together the conditions that will enhance the growth of the plant.

Huber urged his listeners to remember that nutrition is an integral part of efficient crop production both for crop quality and quantity but also in disease control.

Nutrient rate, form, time, source and method of application are important considerations for disease control, he added.

For more information on FHR, the company that sponsored Huber's appearance, visit www.fhr1.com.

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