AGRONOMICS
Micronutrient Info by Dr. Alan Blaylock
Dr. Alan Blaylock, who holds a MSc in plant nutrition, concludes that “Micronutrients are not magic, you need to understand them to maximize them".
Maximum benefit from micronutrients is obtained through good management. We are seeing more benefit and response to micros over time, as soils become more depleted and more responsive hybrid crops are introduced.
Nutrients are taken up by the plant through either mass flow, diffusion or root interception. The micronutrients are primarily taken up by diffusion into the root. The "Root Rhizophere" is a busy place, colonized by micro-organisms that live in an environment largely enriched by exudates which is leakage from the roots themselves. Activity involved in nutrient availability can be affected by many factors, including background levels, pH, organic matter and temperature.
For example, for each point of pH change (say from pH 7 to pH 8), there is a 100 x’s decrease in the availability of Zinc, Manganese and Copper. With each point increase in pH, it decreases Iron availability by 1000 X. Oxygen also affects nutrient availability such as Manganese and Iron.
Adverse soil conditions also affect micronutrient uptake because "the micros don’t come running to the roots" and since roots only explore 1-2% of the soil volume, the way you apply your micronutrient fertilizer is important. You need to pay attention to interactions. For example, high Nitrogen levels delay the transport of Copper from the lower ievaes to the upper leaves in a plant. One must realize that high organic matter complexes or ties up Copper, while lower organic matter means slower decomposition and lower micronutrient release. While we have slow diffusion in high clay soils, we can experience leaching of cations in low CEC or coarse textured soils.
For example broadcasting, while being an acceptable strategy for Boron, is not a great idea for Manganese, Zinc or Iron especially in high pH soils where banding can be 2 to 4X more effective.
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Residual Glyphosate Can Lurk In Soil
By: Bill Strautman, Saskatoon Newsroom
Producers need to be aware of the side effects that can occur in their soil when they use glyphosate, says a professor emeritus in botany and plant diseases at Purdue University in West Lafayette, Indiana,
"We need to recognize that any time we have a major change in agricultural practice, we're going to change a lot of things," Don Huber told a recent Agri-Trend Farm Forum in Saskatoon.
"We may focus on one thing, but we don't just change one thing. There are a lot of other things that change, whether we want them to or not," Huber said glyphosate was patented as astrong metal chelator before it became a herbicide. It immobilizes manganese, which is required for the growth of many plants.
"This compound (glyphosate) impacts plants through mineral deprivation," he said
Glyphosate residues can have a subtle impact on crop development so farmers should be aware of the potential side effects of repeated glyphosate use. For example, because glyphosate immobilizes manganese, farmers can compensate by adding manganese micronutrients. |
"So we need to recognize that fact and then do things that can compensate for some of that reduced micro-nutrient availability for our crops"
Huber said glyphosate can affect many aspects of plant growth.
"It impacts the plant directly as a herbicide," he said.
"It can reduce the efficiency of micronutrient utilization, especially the physiological activity of manganese. Those plants would require more manganese for optimum physiological efficiency. It affects the abiotic environment through chelating nutrients and it's also toxic to rhizobia manganese reducing organisms and certain biological control organisms in the soil.
"It changes the rhizosphere microbiology. We need to recognize what those changes are because it changes the natural biological control or sup-pressiveness in the soil, plus the physiology and resistance mechanisms in the plant. In some cases, through that chelation, it also enhances the virulence of some of our pathogens.
Huber said glyphosate immobilizes enzymes by using physiologic pathways that require manganese, zinc, copper or iron for activity and a strong chelator that can immobilize them.
"Tordon is a strong copper chelator. That's why it is more specific to broadleafs. Copper is more involved in. broadleaf plants than grasses," said Huber.
"If you chelate, you also reduce the efficacy of the glyphosate. That's why most producers add a little ammonium sulfate to their glyphosate mixture. It reduces the chelation with calcium and manganese to keep the glyphosate still active." Huber said 15 years ago he tried mixing glyphosate and manganese to treat manganese deficiencies in soybeans in low manganese soils.
"We could mix them together and keep them in solution, but we didn't get any benefit. We lost herbicidal activity and we couldn't measure any manganese update."
He said tank mixing with zinc is even worse, which is why tank mixing with micronutrients is not recommended on the product label, except in specific situations.
Huber said the longer he's studied glyphosate weed management, the more he's seen manganese deficiency and poor nodulation.
"In some of our soils we're seeing it takes up to four years after moving away from glyphosate before we can re-establish normal nodulation on soybeans and some of our other legume crops.
"It's an area you need to be aware of in legumes. Watch for nodulation. You may need to inoculate in areas you didn't inoculate before because of the gradual reduction in the population of nitrogen fixing organisms.'1
He said Nitragen, an inoculant company in Indiana, has spent 10 years looking for strains of rhizobia that are resistant to glyphosate. It has not published any successful accomplishments, he added.
One of the strengths of glyphosate is that it's systemic, which means it translocates in the plant. Huber said this also means it concentrates in rner-istematic tissue, which is new growth tissue such as root tips, growth points above ground and the crop product itself.
"Late application of glyphosate on Roundup Ready cotton can result in only 20 percent of the bolls staying on the plant because of the concentration of glyphosate in the meristematic tissue" he said.
"We usually have a smaller root system with Roundup Ready crops because of the concentration of glyphosate that holds in the meristematic root tips. “It acts as a reservoir of glyphosate as that material decomposes."
Huber said the availability of manganese varies, with different crop sequences and rotations.
"Continuous corn leaves a whole lot more manganese available for subsequent soybean crops than any of the crop rotations. And soybean has a high requirement for manganese " he said, adding that it's a good fit.
"But when we got into Roundup Ready corn, we don't see this advantage. It looks just like all the other rotations. That's because of changes in the soil micro flora affecting manganese availability with glyphosate usage. And it doesn't have to be with the Roundup Ready crop. It can be an application as a burn down. It changes that micro flora."
Tillage methods can also have an impact. Huber said switching to zero tillage from conventional tillage changes nitrogen relationships and nitrification.
"Denitrification is much higher in no till than in a tilled plot, so residual nitrogen changes with different tillage systems. An important thing to remember is the need for balance and meeting the sufficiency needs of the plant if we're going to have optimum production and product quality."
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Glyphosate Affects Roots
By: Bill Strautman, Saskatoon Newsroom
Drip rates of glyphosate can reduce root uptake of manganese to less than 20 percent, but have little effect on root uptake of iron and zinc, says an American crop scientist.
Drip rates are 2.5 percent of the recommended herbicide rate.
"But when you look at translocation from the root to the rest of the plant, you see for all three that the translocation mechanism is pretty much decimated, even with extremely Sow rates of residual glyphosate," Don Huber told Agri-Trend's recent Farm Forum.
He said researchers have also identified specific enzymes that are inhibited by glyphosate, These enzymes are involved in root uptake of manganese and translocation of other micro-nutrients.
If fanners are aware of the situation they can often offset some of these effects by increasing the availability of manganese.
Huber said there's a lot of data showing glyphosate is quickly immobilized when sprayed (in the soil
"That's true if you put it on the surface. But if you spray it on a weed or a Roundup Ready plan l, it's distributed throughout the entire rhizosphere. Those roots are very leaky and you’ll get the same amount of glyphosate leaching out of a Roundup Ready crop into the rhizosphere as you get from a susceptible target weed."
Huber said when the Roundup Ready gene was inserted into crop plants, it allowed producers to put more glyphosate on more acres.
""We see anywhere from a 10 to 50 percent reduction in manganese efficiency with the Roundup Ready gene present, compared with isogenic lines without it.
"Any manganese in the plant before the glyphosate application will be immobilized. On our low manganese soils, it takes eight to 10 days before the plant recovers. On better soils, it might take two or three days and then the plant is green again."
Huber said farmers have a large window with plants like soybeans to recover the effect on manganese.
"You’ve got about 20 days that we don't see any loss in yield (on soybeans) if we get the manganese levels up in that period of time.
"Corn is a totally different picture. With corn you need to have full (manganese) sufficiency from the seedling stage or you'll have an irreversible yield loss."
Huber said effects of glyphosate have been reported for years, including reduced manganese and iron uptake, immobilization of manganese, reduced nodulation and nitrogen fixation, increased drought stress and earlier maturity. Many of these effects can be reduced with additional manganese applications, he added.
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Disease Severity Increased
By: Bill Strautman, Saskatoon Newsroom
Many plant diseases become worse when glyphosate is used in the field, says an American soil scientist-Many of these diseases are what Don Huber calls root nibblers and haven't yet been recognized as economically important.
"Under our glyphosate management programs, we're starting to see diseases increase in severity," he told. Agri-Trend's recent Farm Forum.
"We can directly demonstrate that glyphosate increases the severity in some of these diseases."
He listed nearly 30 cases where glyphosate increased disease problems, including root rot in barley, crown rot and wilt in canola, and glume blotch, root rot, head scab and take-all in wheat.
"It's nothing we should be surprised about if we realize the relationship of nutrition and disease," Hiiber said.
Producers are beginning to see potassium deficiencies in corn, he added, even though they have followed the traditional potassium application rates.
He said they are not only starting to see potassium deficiency, but also a poor response when additional potassium is applied.
"We know that glyphosate stimulates fusarium
in general," Huber said.
"Richard Dick's work in Ohio State shows that the stimulation of fungi in the soil can actually account for as much as 150 pounds of potassium immobilized—sequestered in fungal mycelium."
Promotes fusarium
Huber said glyphosate was once patented as a herbicide for weed control because it increased fusarium in the target weed.
"If you take glyphosate and put it on a plant in a sterile environment, you will rarely kill the plant. It's only when you have it in a non-sterile environment that you get stimulation of the pathogens. That's how you get good control of most weeds with glyphosate".
The chemical stimulates fusarium organisms. In Alberta, one fusarium species has been implicated in canola wilt disease.
"With head scab (fusarium), the old cardinal principle used to be that we needed flowering, precipitation and temperatures above 80 F all occurring at the same time. That's no longer necessary.
"We now see head scab without the temperature component. That's because temperature and glyphosate do the same thing to the nitrogen metabolism of the plant, and that is what's responsible for susceptibility and resistance to head scab."
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All About Moly
By: Dr. Ieuan R. Evans, Senior Agri-Coach
Moly (molybdenum) is the wallflower of the plant essential micronutrients; no one wants to dance or find out if this lonesome element is present, absent or even around in overabundance. Moly is the only significant micronutrient that becomes more available as the soil pH increases from pH 5 to pH 8.5. In our intensive crop management strategies we take "moly" for granted - no questions, no answers.
In my native Wales, molybdenum was used as a seed treatment on cole crops (kale and turnips) or the usually acidic soil at around pH 4,5 to 6 was limed. This addition of lime increased soil pH and thus the availability of moly. In Southern Ontario moly is routinely added at a few ounces actual per acre to cole crops such as cauliflower and rutabaga on fertile soils at around pH 7. This prevented the disease known as whiptail, a moly deficiency in cruciferous crops that could result in crop failure. In Western Canada I have only seen moly deficiency occasionally in cauliflower and canola, but remember obvious symptom usually means a severe deficiency. In my own garden, pH 6.2,1 can induce moly deficiency in cabbage seedlings by applying very high levels of N fertilizer.
WHAT DOES MOLY DO?
While the actual requirement for moly is low, it's the key element in nitrogen (N) metabolism. The enzymes nitrate reductase, nitrogenase and possibly sulphite reductase all must have molybdenum to function effectively.
In legumes the moly requirement is very large in the root nodules in the role of N fixation. Its function is to convert nitrate to the ammonium form, so it’s not surprising that molybdenum is less important to- crops fed ammonium rather than nitrate fertilizer.
Research has shown (attention: bean and pea growers) that>n soils with low molybdenum availability it is possible to replace the application of nitrogen fertilizer to legumes by the application of molybdenum fertilizer combined with proper rhizobial infection. On field beans, is a seed treatment with moly or a foliar application of a few ounces comparable in price to 100 Ibs. or more of actual N that might be applied to the crop?
I'm beginning to suspect that moly deficiency can occur on high pH soils 7 - 8.5 subject to frequent irrigation; i.e. the moly's been leached out. Could this be happening to dry bean and peppermint crops? On the other hand there could be moly unavailability on soils with a pH of between 5 and 6. Maybe that's why alfalfa doesn't fix N below pH 6 and canola can't utilize all the N of a high yield expectation on acidic soils.
In addition to the well-documented problems with cole crops, moly deficiency causes pollen failure in corn leading to grain set failure and premature sprouting in wheat and corn. Premature sprouting in wheat maybe strongly depressed by foliar sprays of molybdenum particularly in soils high in nitrogen although critic* levels of moly in leaves varies widely between 0.1 and 1 ppm. Seed pelleting of sensitive crops with molybdenum at the rate of 100 gm per hectare or 1 ounce per acre of actual molybdenum trioxide is highly effective Anyone tried this yet? Foliar applications are also highly effective at an early growth stage, particularly on legumes. Just because we never test for mo!y or never use moly doesn't mean that we shouldn't be trying it out on our crops.
On the negative side, high levels of moly cause problems in livestock by inducing a severe imbalance of copper. This situation occurs in many areas of the prairies such as Southern Manitoba and the Swan River region. Molybdenum excess occurs in soils with poor drainage and high in organic matter.
All in all let's tango with Moly ...let's do a series of strip trials or seed treatments with a select number of clients this year - let's plan for it now.
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Diagnosis and Correction of Manganese Deficiency
How Common Is Mn deficiency
By: Doug Penny, Dr. Ieuan Evans and Elston Solberg
On a world scale Zn, Fe, Mn and B are the most common micronutrient deficiencies in crop production. Victor Shorrocks with the Micronutrient Bureau, UK, has stated that, "It is surprising that it (Mn) is not as well catered for as other micronutrients, either with commercial technical service or research associations". In the Prairie Provinces, Mn deficiency is observed occasionally but its extent and frequency is largely unknown. In the Great Lakes Region, Mn deficiency is common on high pH, organic (muck) soils.
Deficiencies in the Prairie Region tend to be sporadic; occurring some years and not others. In addition to the variation that occurs from year to year, Mn availability can also fluctuate markedly within a growing season. These characteristics, plus large differences in among species and varieties in their tolerance to low Mn, make it difficult to determine when Mn fertilization would be beneficial.
Soils Prone to Mn Deficiency
- Highly weathered tropical soils are often low in total Mn. Liming these soils often induces Mn deficiency. The total Mn content of soils ranges between 20 and 3000 ppm (average - 600ppm).
- Mn deficiency also occurs on high pH soils and high organic matter soils in semi-arid, temperate regions. Mn deficiency in these soils is not a result of low total Mn but low plant availability. Mn2+ is the principle species in soil solution and the form that is taken up by plants. Solubility decreases 100 fold for every unit increase in pH, similar to other divalent metal cations. Low Mn availability in high organic matter soils is attributed to the formation of unavailable chelated Mn compounds.
Effects of Soil Moisture, Aeration and Biological Activity
In addition to pH and organic matter, plant available Mn is strongly influenced by soil moisture, aeration and biological activity. Work lead by Don Huber, Purdue University, West Lafayette, Indiana has identified the important role of microorganisms in Mn availability and crop diseases.
An important characteristic of Mn affecting its availability to plants is that it is very readily oxidized from Mn2+ (available) to Mn3+ and Mn4+ (unavailable) by soil microorganisms. Except in very dry and very wet (saturated) soils, both oxidizing and reducing conditions exist. At saturation, all pore spaces are filled with water and reducing conditions dominate, producing high levels of Mn2+. As the soil dries, air replaces water, first in the larger pores and then in smaller and smaller pores, until oxidizing conditions dominate. The high levels of Mn2+ that are generated when the soil is wet provide large amounts of substrate for Mn oxidizing microorganisms. As the soil dries, the population of Mn oxidizers can build up to a very level, depleting the supply ofMn2+. This can result in a period of Mn deficiency that can be quickly reversed by rainfall and warm temperatures. This strong influence of soil wetting and drying and biological activity on Mn availability tends to make the occurrence of Mn deficiencies sporadic and make soil tests less reliable than for other micronutrients.
Deficiency Symptoms and Diagnosis
Prediction of when Mn fertilization would be beneficial is difficult given the sporadic nature of deficiencies. This is further complicated by large differences among species and varieties in their susceptibility to Mn deficiency. While large differences in susceptibility are known to occur, the susceptibility of specific varieties is seldom known and producers usually acquire this information by trial and error. Barley, oats, wheat, peas, potato and soybean are some of the crops listed are being susceptible to Mn deficiency.
About 15 years ago, severe Mn deficiency was identified on some varieties of oat in a regional variety trail at the U of Alberta Research Farm near Edmonton (Evans, Penney and Solberg). While some varieties were severely affected, others were essentially free of deficiency symptoms (Figure 1). On the severely affected varieties, two narrow strips of much better growth were evident on the tractor tracks made when the plots were harrowed after seeding (Figure 1). Two varieties least affected were Waldrin and Calibre, both developed at the Agriculture Canada Research Station, Lacombe, Alberta. Dr. L. J. Piening, Plant Pathologist at Lacombe (retired) indicated that he commonly saw 'gray speck' (Mn deficiency) in the area where oat breeding and selection was conducted. This indicates that at least some varieties developed there are selected for tolerance to Mn deficiency.
Better growth of barley and wheat on wheel tracks has been observed quite frequently in the Prairie Region. At maturity, crops on the wheel tracks are typically taller, and lighter in color (less disease) than off the wheel tracks (Figure 2). When lodging occurs, the crop on the wheel tracks tends to stand.
There has been some concern for negative interactions between copper deficiency and some herbicides. In areas where copper deficiency is a concern, Dr. leuan Evans has postulated that these strips may be tracks created during crop spraying for weed control and that the impact of the herbicide is reduced on the wheel tracks. Given some of the more recent insight into Mn deficiency and its interaction with diseases, it seems plausible that some of the observed better crop growth, and resistance to lodging and diseases on wheel tracks is a result of increased Mn availability. Soil compaction on the wheel tracks slows drying, reduces aeration, thus maintaining reducing conditions and Mn availability for longer during dry periods.
The main manifestations of Mn deficiency on crop growth are:
- Reduced cell division and cell elongation (cell elongation is affected more than cell division). It has been reported that Mn deficient barley plant take twice as long to reach the boot stage as non deficient plants; and
- Reduced lignification, which makes plant more susceptible to lodging and disease.
- Low pollen fertility, resulting in fewer kernels per head.
- Reduced 1000 kernel weight resulting from a shortage in carbohydrate supply for grain filling.
The fungus that causes 'take-all' root rot of wheat (Gaeumannomyces graminis), and other root pathogens, has been shown to be strong Mn oxidizers. The organisms reduce Mn availability, thus reducing lignification of roots, making them more susceptible to infection. This suggests that Mn deficiency may be more of an issue when disease pressure is high in continuous wheat rotations.
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