Their gestation and even lactation diets are made up of nearly all forages. Fortunately, nitrate testing of forage samples is not expensive, and if a winter feed inventory is discovered to contain toxic levels of nitrates, effective measures can be taken to correct beef herd feeding programs that reduce most nitrate threats.

I was taught a long time ago that nitrates accumulated in many types of forages usually caused by bad weather, despite a small number of forages that are known as good weather high-nitrate accumulators. Some of those damaging weather conditions/forage combinations are as follows:

• Hailed cornfields, alfalfa and oat crops.
• Drought overshadowing a cornfield.
• Cool, cloudy and wet growing season in alfalfa and other legume crops.
• Early frost in immature cornfields, oats, alfalfa and other legumes.
• Excessive wind that blows over corn plants and causes severe lodging in cereals.

When sunny weather prevails between timely rain showers, nitrates and other nitrogen compounds are naturally taken up by the plants’ roots and transported through the stems and finally to the leaves.

Photosynthesis converts these nitrates into leaf protein. However, when one of the above bad weather conditions interferes with nature, nitrates have literally nowhere to go and tend to accumulate to toxic levels in the lower portion of the plant.

Ironically, nitrates do not cause nitrate poisoning in beef cows.

That’s because the real culprit is an intermediate compound, nitrite. When cow herds consume forages with natural low levels of nitrates, the ruminal microbes break down this nitrate into ammonia, which is safely incorporated back into bacterial protein. In contrast, excessive forage nitrates overwhelm the microorganism’s capacity to process the nitrates into ammonia, and a nitrite pool is formed.

These nitrites are absorbed across the rumen wall into the bloodstream, where they bind with the oxygen-carrying compound hemoglobin, present in cow’s red blood cells. Unlike hemoglobin, methemoglobin cannot carry oxygen in the blood. As a result, the oxygen-carrying-capacity of the cow’s blood quickly diminishes to the point where the tissues of a poisoned cow suffocate to death.

All nitrate-suspected forage (such as a hailed-out barley crop or drought-stricken corn field) should be tested before feeding to cattle as the best assurance for safety. Producers should collect samples in the field and then collect another set of samples once the crop is harvested. Send in all samples into a reputable laboratory and request a common nitrate test, which should cost no more than $20 per forage sample. It is also recommended that water samples be collected and tested for nitrates too.

A routine laboratory printout shows forages and other feeds analyzed for nitrate content are commonly reported as nitrate (NO₃) or nitrate nitrogen (NO₃N).

Research has proved that mature cattle and replacement heifers can safely consume a total diet containing nitrates that are below 0.5 per cent NO₃, or, expressed another way, below 0.12 per cent NO₃N on a dry matter basis.

Blending down

I believe that if overwinter forages are sampled and the results show that they contain toxic nitrate levels for the cow herd, it is a good idea to grind the contaminated forage such as hay and dilute it with other clean hays, straw and silage.

This process often brings the level of nitrates to acceptable safe limits, particularly in a TMR mixer. Note that the alternative of feeding whole high-nitrate bales alternated with low-nitrate bales is not recommended.

Last winter, I dealt with a 250-beef cow-calf operation that tested an overwinter supply of hailed alfalfa-grass hay bales that contained 0.70 per cent NO₃ (on a dry matter intake (DMI) basis). In order to safely feed it, we diluted it down to under 0.5 per cent NO₃ (on a DMI basis) by putting a reformulated TMR diet together.

TABLE: A ration formulated to reduce the impact of high-nitrate forages in a beef cow diet. Source: Peter Vitti

Actual calculated NO₃ level of this diet was 0.46 per cent (DMI basis). The producer fed this overwintering diet, when his cow herd was brought home in late October until the start of the calving season in February. Then a couple of pounds of barley were fed to each fresh cow. No problems associated with the nitrate-contaminated hay appeared.

This story is a good testimonial that feeding high-nitrate forages to overwintering beef cows can be done. This means suspect forages should be tested for nitrate content. If its nitrate content comes back and it cannot be safely fed, dilute it to a safe feeding level with low-nitrate forages in a well-balanced overwintering beef cow diet.

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Prairie farmers use about one million metric tonnes of phosphate fertilizer annually, which has a value of over $1 billion. It is important that farmers and agronomists have a very good understanding of soil phosphorus and phosphate fertilizer management to help ensure fertilizer is carefully used and money is wisely spent.

In this article, I will focus on understanding soil phosphorus and, in my next two articles, will discuss soil P testing methods and developing wise phosphate fertilizer recommendations.

The soil P cycle

To understand soil P, it’s important to understand how P cycles in soil. The major processes of the P cycle include:

• adsorption of P onto surfaces of inorganic constituents;
• uptake of P by plants;
• cycling through plant residues; and
• microbial influences through immobilization and mineralization.

Both inorganic phosphorus (Pi) and organic phosphorus (Po) occur in soil. Both are important sources for crop nutrition. A great deal of research has been conducted in Western Canada in the past 40 years to understand the soil P cycle. Figure 1 shows a simple illustration of the P cycle.

The left side of Figure 1 shows the various forms of Pi which come from the parent materials on which soils have formed. During soil development, primary P minerals very slowly dissolve to provide P ions to the soil solution. The solution P can be taken up by plant roots; adsorbed to mineral surfaces; precipitate with various cations to form secondary P minerals; or incorporated into the biomass and soil organic matter. The fate of soluble Pi depends on the physical and chemical conditions in the soil environment.

Depletion of solution P by plant roots can cause a rapid replenishment by exchangeable and labile P forms. “Labile P” refers to a pool of soil P that is less available to plants but can undergo rapid chemical or biological changes to recharge or replenish the soil solution P. As the labile P forms become depleted, nonlabile secondary P minerals slowly solubilize to maintain the labile Pi pool. Concurrent to the dynamic interchange between Pi fractions, the cycling of Po also contributes to the maintenance of P in the soil solution.

Microbial P is the active hub of the Po cycle. Organic P can be taken up by soil organisms or can be mineralized to enter the soil solution as Pi. Po can also be stabilized as part of the soil organic matter or interact with soil minerals.

Carbon (C) inputs, derived from litter and plant residues, provide the energy to drive the system by stimulating microbial activity. When C inputs are lacking, the turnover of labile Po slows down, and maintenance of solution P is limited to the quantity of labile Pi. Conversely, larger C inputs may result in the immobilization of solution P in labile and stable Po forms. Figure 1 shows a simplification of the P cycle but tries to portray the dynamic nature of soil P.

Crop rotation effects on soil P

In the 1980s, the University of Saskatchewan developed a sequential extraction technique to characterize the various Pi and Po forms and amounts (Figure 1). We used the technique to look at soil P changes in long-term cropping studies at Agriculture and Agri-Food Canada’s Lethbridge Research Centre on Dark Brown soil (Rotation A-B-C) and the University of Alberta’s Breton Plots on a Gray soil. We found that crop rotations and fertilizer management had dramatic effects on most Pi and Po pools. Among the observations:

• Not adding P fertilizer resulted in a continuous drain on almost all inorganic and organic P pools.
• Leaving the soil in fallow every second year accentuated the drain on Po pools.
• The addition of fertilizer inputs at both Lethbridge and Breton resulted in more dynamic P cycling. Phosphate fertilizer addition increased the size of all Pi and Po pools at both sites.
• The continuously cropped treatments that received both N and P fertilizer inputs had the highest total soil P levels of all cropping treatments.
• Continuous cropping and additional P fertilizer inputs had the most positive effects on soil P cycling at both sites.
• Continuous cropping, and the addition of both N and P fertilizers, resulted in benefits to the health and quality of soil P cycling at both long-term research sites.

Plant uptake of soil P

Many physical, chemical and biological factors affect plant uptake of soil P. In the top 20 cm (eight inches) of surface soil, plant roots occupy and contact less than one per cent of the soil volume. As a result, only an exceedingly small amount of P at the root surface is intercepted and absorbed by roots.

Most of the P taken uptake by roots is by mass flow and diffusion. As roots absorb water from the soil solution, a convective flow of water moves toward roots carrying P by mass flow. However, mass flow toward plant roots is often not sufficient to supply plant P requirements. As P is taken up by root hairs, the P concentration in solution near the root surface is reduced. This creates a P concentration gradient radiating from around the root. This causes P to diffuse toward the root along this gradient from an area of higher concentration toward the root surface where the P concentration is lower.

The proportion of P supplied by interception, mass flow and diffusion mechanisms depends on root characteristics, rate of water absorption and the levels of solution Pi and adsorbed P on the soil surface.

The soil-plant root interface is referred to as the rhizosphere. The rhizosphere zone is very dynamic in which living roots release exudates into the soil. These organic compounds stimulate microbial activity. As a result, the population of microorganisms in the rhizosphere zone can be up to 10 times higher than in the bulk soil. In P-deficient soils, microbes in the rhizosphere can intercept P before it can be taken up by roots. The release of organic C by roots into the rhizosphere affects the solubility and uptake of P and other nutrients.

The conditions in the rhizosphere differ from bulk soil, in that the preferential uptake of ions and water results in depletion or accumulation of ions in the rhizosphere. Prominent pH change in the rhizosphere is caused by differences in the cation/anion uptake, especially with nitrate-N (NO3- -N) and ammonium-N (NH4+-N) supply. Nitrate is negatively charged, and ammonium is positively charged. Preferential uptake of cations such as NH4+ result in higher net excretion of rates of hydrogen (H+) causing a pH decline in the rhizosphere. Preferential nitrate-N uptake results in higher net excretion of rates of hydroxyl ions (OH-) causing an increase of rhizosphere pH. The portion of P in soil solution can be influenced by changes in the rhizosphere pH. The ability of plants to preferentially change the pH at the soil-root surface can be a significant factor in influencing soil P availability and uptake.

Fine root hairs, which are tubular extensions of root cells, are a result of lateral cell growth and can increase the surface area of the outer roots by two to 10 times. Root hair length varies from 0.1 to 1.5 mm. Root hair density varieties from 50 to 500 million per square metre of root surface. Most plants have root hairs; however, some crops, such as canola, only have an extremely small amount of root hairs or none at all. Root hairs can aid in ion uptake by plants and are most important in the uptake of immobile nutrients such as P.

Vesicular arbuscular mycorrhizae (VAM), which are soil fungi, can form a symbiotic relationship with plant roots of some crops. The mycorrhizae use plant carbohydrates for their growth and in return supply nutrients for plant growth. The primary benefit of VAM is to form hyphae that extend from the plant roots to increase P uptake, water and other nutrients such as copper and zinc. VAM is particularly beneficial in soils with low plant available P. However, not all crops can be infected or benefit from VAM, such as canola.

Labile organic P compounds can be mineralized rapidly in soils by an enzyme produced and released by roots called acid phosphatase. Some research has shown that plant-produced phosphatase can hydrolyze Po for improved plant nutrition. More research is needed to better understand which plants can produce and release acid phosphatase and the benefit to P crop nutrition.

The interaction between soil and plant roots is highly complex and is influenced by soil types, crop species, root characteristics, forms of root exudates, pH changes in the rhizosphere, microbial activity, types of enzymes produced, and influence of VA mycorrhizae.

Summary

This is a brief explanation of the soil P cycle, effects of cropping and fertilizing on soil P, and soil-plant root factors that affect plant uptake of soil P. Research here in Western Canada has clearly shown that continuous-cropped soils, with the addition N, P and other needed fertilizers, have resulted in the greatest benefits to the health and quality of soils and to good P cycling in soils.

In my next two articles, I’ll discuss testing methods for plant available soil P and how to develop wise fertilizer P recommendations.

The post Understanding soil phosphorus, part 1 appeared first on Grainews.

For many soil science folks, the world ends when their knuckles hit the ground with a four-foot hand auger. My interest in what goes on beyond normal soil profile depth began with my very first research project on nitrate-nitrogen (nitrate-N) leached to greater depths and, perhaps, contaminating wells.

Nitrate-N leached below the root zone under various cropping practices

The depth objective was 20 feet but with the equipment we had at the time that depth was seldom achieved.

A special site comparison included the then-Federal Forestry Farm on the eastern edge of Saskatoon. There was a site between tree rows that had been continuously summerfallowed for 10 years. At that site, the nitrate-N to a depth of 16 feet was more than 1,200 pounds per acre (see Table 1). The crop/fallow rotation also had considerable deep nitrate. The native prairie had almost no nitrate and was so dry we could only get to eight feet.

Keeners who wish to read the entire project report can find it online. For that project, “deep” was 16 feet.

If any reader who wishes to learn more about nitrate in farm wells and infant death from blue baby syndrome, you can check out this link. This column has dealt with that topic many times over the years.

Soil salinity and ‘deep’ groundwater

This was the “biggie” that shattered accepted norms and put us on a very different trajectory — down, down deep. This file was where we really got into the “deep” category. In the late 1970s, soil salinity was running rampant. The early 1970s were very wet and raised water tables. The late 1970s dried out and evaporation did its thing and left white crusts in your face.

Southern Alberta was a hot spot for salinity and the prevailing wisdom was sidehill seep was the major mechanism. Water came in at the tops of hills, went down until it hit an “impermeable” layer and moved sideways until it came out as a sidehill seep. The solution was to plant the hilltops to alfalfa to suck up the excess water and the problem would be solved.

I had spent much time in the literature and came across a few references that talked about artesian discharge. I did not believe the sidehill seep model fit our situation and knew we needed a different approach.

After many months of negotiation, we were provided a grant to purchase equipment and vehicles to go to actual farms around the province and determine the cause of the soil salinity. The provincial ag reps (extension agents) suggested sites. The year was 1982.

A Sterling Drill was in common use, and we considered it. However, the maximum depth was 20 feet — but what if the answer was at 21 feet? We bought a Mobile Drill with enough auger to go in 43 feet. We also had a mobile lab to do analysis on the spot to further guide the work.

At our Shaunavon site, we drilled several 20-foot holes and took foot samples and analyzed them for salt, etc. Some were salty, some were clean, with no apparent reason. So, we picked a site in the middle of a very salty grass patch and hung it all out — 43 feet. Still no answer.

At that time, I consulted famous glacial geologist Earl Christiansen and hired him as a consultant. He said we were doing it all wrong. Soil science may be a “top-down” affair, but geology is a “bottom-up” business.

He hired a water well driller with a hydraulic rotary drill to drill right beside our 43-foot hole. Guess what? The answer was at 53 feet where the Shaunavon aquifer came in with enough pressure that the static water level was just inches below the soil surface.

The rest, as they say, is history. We went on to drill many flowing holes in salty areas at various depths up to a few hundred feet. Soil salinity on the University of Saskatchewan Goodale Farm is caused by a glacial aquifer 130 feet down with pressure to shoot water 15 feet above ground.

Water table and crop water use

All of the years we measured soil water use by crops, the water table was not part of the equation. We are a dry climate, so the water table is below rooting depth — or so we thought. It was not until many years after I was officially retired that we learned differently — and that was on my Dundurn farm.

In 2012, I did a crop tour in mid-July with my Dundurn neighbours. There had been little rain in previous weeks. In a flat part of my hilly ground the wheat crop was doing well. I expected the topsoil to be so dry that the soil probe would not go in. To my surprise, the soil probe went in like butter.

My conclusion was that a near-surface water table must be the reason. The neighbours were skeptical but after the tour was over, I installed, by hand, a 10-foot observation well. The water table was about 4.5 feet and capillary rise would keep the roots well supplied with water. The 20 inches of rain in 2010 was 10 inches more than the crop needed. We now know that would raise the water table by about eight feet.

The results of that and many other water table wells have been documented in Grainews several times.

For water table and crop water use “deep” is about 10 feet. If the water table stays below 10 feet at all times, it will not be a factor.

Reverse polarity to downward water flow and real deep comes into play

A few miles east of Gardiner Dam at Diefenbaker Lake, the soil survey in the 1970s did detailed work on a 40-acre parcel in a field of Weyburn loam soil — specifically, glacial till soils with low-relief hills and sloughs.

One large slough received special attention and detailed samples were taken to 20 feet. The soils were completely free of salts to 20 feet.

In this area, we had completed the deep geology as part of previous irrigation investigations. Beneath the site with highly leached sloughs there was a pre-glacial aquifer at a depth of approximately 300 feet. That aquifer drains to the South Saskatchewan River, so the head is very low. There are no other shallow glacial aquifers to interrupt the downward flow. Downward ever downward, slow by slow but every hour of every day for centuries.

In this case, deep was 300 feet.

An example of such deep drainage happens right on the University of Saskatchewan land. Just east of Preston Avenue and north of College Drive, there is a large shallow slough that fills up each spring and after each fast rain. Despite being clay soil that slough empties quickly — it flushes almost like a toilet.

Existing geology suggests there may be a deep (approximately 120 feet) pre-glacial aquifer that drains to the South Saskatchewan River west of the site.

It would be a great field lab for students if someone would drill at the site and confirm the geology and the downward gradient to the pre-glacial aquifer. Unfortunately, no one seems interested.

The bottom line: How deep is deep?

Deep for soils folk is the depth of the soil profile — approximately four feet. Soils is a top-down affair.

Deep for geologists depends on the nature of the investigation. It can extend hundreds of feet. Geology is a bottom-up affair.

The elixir that ties soil science to geology is water. Water flow that influences soils can be by upward movement or downward movement.

Have we stretched your brain just a little bit? Those who have Henry’s Handbook of Soil and Water might wish to read Chapter 12 to learn about the many examples that show how it all works.

The post Les Henry: How deep is deep? appeared first on Grainews.

“There’s lots of data that shows seeding early has a significant benefit to yield,” he says, adding that for most crops it can be up to two per cent a day.

“If you can … start seeding five days earlier because you don’t have to worry about applying fertilizer, that can, right off the bat, give you around a 10 per cent yield advantage.”

Fall is also often the time when farmers can take advantage of lower fertilizer costs. Weir, who makes a point of tracking prices, says, “Ninety per cent of the time at least, fertilizer is significantly cheaper in the fall than in the spring. So that’s a big plus.”

John Heard, a soil fertility extension specialist with Manitoba Agriculture, says fall fertilizer applications continue to be a well-accepted practice, particularly in Manitoba.

“It works well with our production system here,” he says. “I think our fertilizer use surveys have shown somewhere between 35 and 45 per cent of (Manitoba) farmers put down fall fertilizer, and often (that’s) banded anhydrous ammonia or banded urea.

“We do less zero till than Saskatchewan and Alberta,” Heard says, adding farmers there favour more one-pass seeding and fertilizing.

“We certainly have some of that here. But, for now… rightfully or wrongfully, there’s more tillage being done in Manitoba, and that fall anhydrous ammonia pass sometimes just does the job.”

Of course, fall fertility applications may not be an option if Mother Nature doesn’t co-operate. “Sometimes, you just can’t get it done,” says Heard, noting the unusually wet fall two years ago prevented many western Canadian farmers from laying in fertilizer on time.

“In those cases, then farmers need to develop a Plan B, which is often a spring application of some description, but it may be one they’re not really set up to do with (their) equipment,” he says.

Heard says producers who miss the fall window for fertilizer applications can plan with their agronomists how to meet their fertility needs later. However, if too many farmers are in the same position, he adds, they could face a supply squeeze the following spring.

“A lot of our fertilizer dealers here, too, are not all set up to deliver and apply all the fertilizer in the spring. They really count on this fall application to get a good bunch of the nitrogen out,” says Heard.

Avoid nitrate forms of fertilizer

Nutrient losses are always something to consider when formulating fertility plans. Heard and Weir caution farmers against fall applications of nitrogen in a nitrate form because that’s when it’s most susceptible to losses caused by denitrification, volatilization and leaching.

“We’re not fans of nitrate forms going down in the fall,” says Heard. “(They) are vulnerable to losses right off the hop.”

Heard doesn’t recommend using urea ammonium nitrate for that reason and says better choices for fall applications are anhydrous ammonia, urea or an enhanced efficiency product like ESN or SuperU.

“Ammonium sulphate, generally used as a sulphur source, can provide nitrogen also,” he adds. “(It’s) best put down late in the fall so that nitrogen stays in the ammonium form rather than the nitrate.”

Heard says when it comes to fall fertilizer applications, in-soil banding is generally considered a much better option than broadcasting fertilizer on the soil surface. That’s because banding not only inhibits nitrate conversion but also helps protect fertilizer from immobilization by soil microbes, leaving more nutrients available for plant uptake.

If nitrogen is broadcast rather than banded, it becomes readily accessible to soil microbes, which will use it to decompose straw before the nitrogen is available for use by crop roots, Heard explains. “We want (soil microbes) to decompose straw, but we want them to be second in line behind our crop plants,” he says. “We don’t want them to be first in line.” 

Heard says for optimal performance, it’s best that fall-banded fertilizer is not disturbed during spring tillage or seeding operations.

When banding anhydrous ammonia in the fall, it’s important the ground be sealed behind the knives to reduce the risk of nitrogen loss. Heard says the best time to do this is when the soil isn’t too wet or too dry.

“We like to have moist soil ideally to do that, then we have good tilth, meaning those slots can close up nicely and the moisture is there to hold (in) the ammonia also,” he says.

Heard suggests one way to assess soil conditions in a field is to do a test run with the fertilizer applicator to assess how cloddy the soil is and whether it can pack well enough to provide a good seal. Farmers can also do a short pass with anhydrous ammonia and then go back to check whether there’s a strong ammonia smell.

“If it’s unbearable, well, then you stop,” says Heard. “You park, and you wait for better moisture conditions.”

Heard and Weir agree farmers should avoid applying fall fertilizers into wet soils (or fields that are likely to become waterlogged) because that’s asking for trouble.

“If you’ve got a low lying, poorly drained field, that’s not where I put on a fall banding or fall treatment of any sort,” says Weir.

Wait for soil to cool down

Fall-applied nitrogen is best applied banded when soils have cooled down to 5 C, or are at least below 10 C at depth, says Heard. At those temperatures, it will tend to remain in a stabilized form until spring, reducing the risk of ammonia to nitrate conversion and subsequent nutrient losses.

“The cooler it is, the less conversion there is,” Heard says. “When it’s warm, it’s much quicker.”

Heard and Weir say on most Prairie farms, optimal soil temperatures will usually occur around Canadian Thanksgiving.

Heard says farmers may be tempted to apply nitrogen earlier if they have time, particularly if there are attractive pricing offers from fertilizer dealers, but they could end up regretting the decision. “If it was to be put on (too) early, even nitrogen that’s in anhydrous ammonia will convert from the ammonium form to nitrate, and then it is vulnerable to losses.”

Heard says nitrogen losses with early applications don’t always occur, noting that fall banding on warm soils performed as well as — or better — than spring banding at some Manitoba research sites located on well-drained upper slopes. Early banding on warm soils did result in high nitrogen losses in wet conditions with poorly drained, depressional soils, however.

As Heard points out, farmers do have options if they’re planning an early fall fertilizer application when conditions aren’t ideal.

“If a grower makes a decision to apply at what we would normally consider an inappropriate time, now, fortunately, we have some technology that allows him to do some of that while reducing the risk,” he says.

These technologies include nitrification inhibitors, like N-Serve or Centuro for anhydrous ammonia and eNtrench for urea, which contain ingredients toxic to nitrifying bacteria that help keep fall-applied nitrogen in the ammonium form, says Heard. SuperU has both a nitrification inhibitor and a urease inhibitor, which slows the initial conversion of urea to ammonia, he notes.

Weir maintains nitrification inhibitors can be useful in situations where there are variable moisture levels within a field. If there are low spots that aren’t as well drained as the rest of the field, for example, a nitrification inhibitor can be added to delay ammonia to nitrate conversion in those areas.

Weir says controlled-release products like ESN, a urea fertilizer with a polymer coating, are another option for farmers considering early fall nitrogen applications. These products can reduce losses by delaying the initial release of nitrogen and providing it gradually to better match crop uptake needs.

The urea in ESN needs warm, moist conditions in order to leak out of the polymer and into the soil, which physically reduces the amount of product that is available for losses in the fall, especially in dry conditions, Weir notes.

He says some farmers will blend ESN with regular urea and then band it as a way to hedge their bets if conditions worsen after fall applications. “If they lose 50 per cent of the urea, they’ve still got all the ESN, so it’s an insurance program,” he says.

Consider co-banding phosphorus

Putting in phosphorus not only helps replenish fields depleted in the nutrient, but it can also boost yields.

Fall can be a good time to apply phosphorus, since it doesn’t move around as easily in the soil as nitrogen and is less susceptible to losses as a result. It’s also a way farmers can spread out their phosphorus programs, so that what’s being put in at seeding time doesn’t exceed seed-safe rates.

“If they’re putting on fall nitrogen anyway, that’s an opportune time to co-band phosphorus with their nitrogen,” Heard says. “We see that as another gold star practice that doesn’t encumber spring fertilization and reduces risk of damage from you having to put down too much phosphorus with the seed.”

Heard says the dual placement of phosphate with nitrogen will tend to increase the availability of the phosphorus to the following year’s crop due to the acidifying nature of anhydrous ammonia. Banding phosphorus and nitrogen together also keeps the phosphorus under the soil surface so it’s less vulnerable to losses from runoff and snowmelt.

Monoammonium phosphate is a widely used source of phosphorus and nitrogen. Weir says it works well on its own or blended with other products like urea, ESN or SuperU in a banded fall application.

Weir recommends farmers who do this save some phosphorus to put in with the seed row in the spring. Heard agrees. “Certainly, we advocate some starter phosphorus in the spring to provide some nutrition until the seedling reaches those bands,” he says.

By co-banding nitrogen, phosphorus and, if needed, sulphur in the fall, it can make things easier and safer for farmers come spring seeding time, adds Heard.

“Canola crops need sulphur and ammonium sulphate is harsh (when placed) in the seed row of canola,” he says. “If you can co-band your ammonium sulphate, if that’s what you’re using, with your nitrogen in the fall … (that’s a) good spot to put it in.”

Weir maintains some growers are moving away from putting down sulphur at seeding time because of toxicity concerns with ammonium sulphate as well as some handling issues.

“It takes up moisture and can cake in the air drills and stuff like that, so a lot of guys are looking for alternatives,” explains Weir. By applying ammonium sulphate in the fall, he says, this enables farmers to get their sulphur in and a good chunk of their nitrogen out of the way as well.”

Farmers who use ammonium sulphate likely won’t have to apply any more sulphur to their fields for the following three cropping years, Weir adds.

The post Your fall fertility primer appeared first on Grainews.

My photograph of a southern Manitoba cornfield in mid-August shows one of the worst cornfields I have ever seen. It tasselled out early with curled grey leaves and no visible cobs on its stalk. Most whole plants were half-parched from the ground up. Oddly enough, I found another field about five kilometres down the road which was also drought-stressed, but was green and had small cobs. Both cornfields are a good testament that silage samples should be collected and tested.

Dairy producers should take several samples of chopped whole-corn plants during harvest. Chopped samples from before and after ensiling can be tested for moisture content using a microwave oven or commercial moisture tester. Subsequent ensiled samples should be sent to an accredited lab for a nitrate test, mould and mycotoxin analysis and a complete nutrient profile. Once received, results can be reviewed to assure forage safety (nitrate, mould/mycotoxin) for being fed to dairy cattle, and that any compromised nutrient values (including moisture content) are adjusted in their diets.

Testing is critical

As a dairy nutritionist, I believe a nitrate test is the most valuable test when feeding drought-stricken silage to dairy cows and other livestock. I have known a few dairy producers who accidentally fatally poisoned young dairy stock with nitrates. They failed to test silage for it.

When dairy producers receive their nitrate results, they should compare them with guidelines shown in the table to establish the degree of animal safety of their corn silage. They should also take into account extenuating factors (age of cow, stage of pregnancy and health status) which determine the final amount of nitrate-contaminated corn silage that can be fed safely.

In addition to a nitrate test, I recommend corn silage samples be tested for mould counts and a mycotoxin screen. We might want to do a specific test for aflatoxins (or the root fungus, Aspergillus flavis). Even though it is rare in western Canadian crops, it may show up since it flourishes in weather that is hot and sunny, warm at night, and dry during the corn silk and fill stages — weather that was typical to us this summer.

When ingested by dairy cattle, aflatoxins greater than 500 ppb in corn silage (dm basis) cause a host of serious health and metabolic problems. Such symptoms include reduced feed, dry matter intake and feed efficiency, leading to reduced milk production, increased liver and other organ damage, failure to process dietary nutrients, impaired immune function, reproductive failure, infertility and even abortions.

Compared to tests for nitrate and mould/mycotoxin field tests, moisture poses no threat to the dairy cows, but in failure to send away those “before” ensiling samples we might miss the best opportunity to store drought silage in its best possible condition. For example, optimum corn silage fermentation occurs when the whole plant is between 65 to 70 per cent moisture. This is the moisture “gold” standard for making corn silage in horizontal bags and bunker silos, with a slightly drier allowance in tall tower silos.

Ensiling this dry corn silage of less than 60 per cent moisture might not allow it to be packed tight enough and exclude most air to be fermented and well-preserved. That can result in undesirable organisms such as blue penicillin moulds to thrive under such low oxygen levels and limited moisture, which creates unpalatable poor corn silage coming out of the opened bunker.

Similarly, drought corn silage samples should be routinely taken and tested for any compromised nutritional values, especially once the silo, bunker or bags go through the complete 21-day fermentation process. Results from these tests (Nel, protein, ADIN and starch levels) can be very useful in taking corrective action when implementing new drought corn silage into the reformulated dairy diet.

In any case, dealing with the challenges of drought corn silage is just the norm this year across Western Canada. The key to effectively using it in dairy diets is to test it for moisture, nitrates, moulds and mycotoxins and its actual nutrient value. Afterward, we can treat it as straightforward forage, which is not really different than normal corn silage.

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So why, anecdotally at least, does the practice seem to be on the increase?

Bigger farms and a shortage of labour could be part of it. Moreover, nobody knows when poor weather will shut down field operations. And there’s Manitoba’s Nov. 10 nutrient application deadline — a regulation meant to prevent fertilizer from being applied on frozen ground, making it more susceptible to run-off, which can contaminate waterways and lakes.

But broadcast nitrogen, especially in warmer soils, or soils that later become saturated, can be lost to the atmosphere, adding to the greenhouse effect and climate change.

With the Manitoba government close to announcing its climate change policy, which will include a price on carbon, some observers worry fall nitrogen broadcasting could trigger additional regulations.

“The Manitoba Fertility Guide… shows an average of 40 per cent less efficiency for N (nitrogen) fertilizer that’s broadcast in the fall, compared to banded in the spring,” University of Manitoba soil scientist Don Flaten said in an email Oct. 5. “This issue of poor efficiency of fall broadcast N is even worse if the soils are waterlogged in early spring.

“For fall banding N, it’s important to band as late as possible, especially for low-lying areas of fields that might be ponded with water during snowmelt.”

In a perfect world farmers would band nitrogen in the spring nearest the time it will be used by crops. But then there’s the art of the possible. There are only so many hours in a day and the weather has to co-operate.

If spring banding gets the gold medal, other techniques and timings have varying results, Manitoba Agriculture soil fertility specialist John Heard said in an interview.

“Banding has a distinct advantage over broadcasting,” Heard said. “There’s a big advantage of spring over fall application, especially with wet falls and springs. The real loser in the story is fall broadcast. Even worse is fall broadcast early in the fall on warm soils.”

Last week one field Heard checked was 15 C at three inches deep.

“If soil was to stay at 15 C, (fall) banded urea could convert entirely to nitrate within 25 days or so,” Heard said. “It means by freeze-up a sizable portion of that (nitrogen) would be in the nitrate form, which could be very vulnerable to leaching or denitrification.”

Benefits of banding

When nitrogen is applied it’s in the ammonium form, it’s stable. It has a positive charge and locks on to clay and organic matter. But warm soil bacteria are more active converting ammonium to nitrate, which can be used to nourish plants, but also be lost to atmosphere.

Banding nitrogen in cool soils helps avoid those losses in a couple of ways. One is bacteria are less active then. Another is the band itself is toxic to bacteria, although over time the conversion to nitrate occurs.

“If you apply (nitrogen) later (in the fall) the microbial activity is thwarted,” Heard said. “If you apply it in a band you further thwart that bacterial activity promoting conversion to nitrate.”

Many farmers like to apply anhydrous ammonia in the fall because it’s usually cheaper than other forms of nitrogen. Heard said it’s a good choice because that form requires in-soil banding. Farmers who apply anhydrous ammonia or urea nitrogen early can slow the conversion to nitrate with various nitrogen conversion inhibiters, he said.

Another disadvantage to broadcasting nitrogen is having it get tied up with crop residue called immobilization. That’s not an environmental concern because eventually that nitrogen will be available to future crops. The problem is a portion of it may not be available for early-season crop growth.

Not only is fall broadcast nitrogen vulnerable to losses in the fall, but in the spring too.

“If the soil is saturated we know that we can lose nitrate-N, even in the spring when the soils are quite cool, two to four pounds of nitrogen per acre, per day,” Heard said.

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• Nitrate-contaminated farm wells have been known since 1945 when the first case of infant “blue-baby” was related to a contaminated farm well in Iowa.
• A 1948 survey of 2,000 Saskatchewan farm wells found 18 per cent had nitrate above the safe drinking water limit. Small farms with livestock and shallow wells were the usual culprits
• Small towns with sandy soils, hand dug wells and outhouses also had nitrate-contaminated wells. Bounty (in Saskatchewan, near Milden where I was raised) was one such example. Bounty is now a ghost town.
• This old fossil sees red when some Janey/Johny come-lately does a survey of farm wells, finds some contaminated with nitrate and puts the cause to all the nitrogen fertilizer we pour on, or intensive livestock.

For a more complete treatise on nitrate in our agriculture, use Google to search for “Fertilizers and Groundwater Nitrate,” and you should be taken the Saskatchewan Water Security Agency website where you can download a PDF. This booklet was prepared by Les Henry and Bill Meneley, sponsored by the then Western Canada Fertilizer Association.

Nitrate rare in native systems

An early research project we did (1970) was deep soil sampling (about 20 feet) of various situations to measure nitrate. In the native prairie at the University of Saskatchewan Kernen farm, nitrate was a rare beast. Any time a nitrate molecule was so bold as to pop out of the soil organic matter (mineralize) a grass root was laying in wait to gobble it up and put it back into organic form.

We must accept that much of the nitrate now moving around in our soil and water came from something that mankind has done. We in agriculture are a part of that.

When the prairie sod was broken much nitrate was released but early crops eagerly soaked it up. Before the white man came to the Canadian Prairies the only nitrate would be at buffalo kill sites and perhaps a few places where our first peoples lingered too long.

Nitrate in tile drains

The first documented nitrate in tile drains was at the famous Rothamsted Research, U.K. In 1870 they installed drain gauges in fields that were clean cultivated and not cropped. Those drains were monitored for about 40 years continuously with no change in management (continuous fallow). At the start, the soil lost about 45 pounds of N per acre per year as nitrate washed away. By the end of the experiment in 1915 the soil was worn down but still lost 25 lbs. N/acre as nitrate.

Fast forward 100 years to the major corn and soybean states of the U.S. mid-west. About 50 million acres of prime land in that area has surface or tile drains; much of it drains to the Mississippi River and eventually the Gulf of Mexico.

A lot of U.S. soil/fertilizer/cropping research of the past two decades has been documenting the significant loss of nitrate and the impacts down the line. Not a pretty picture. The research also includes ways and means to minimize the loss to ag and the impact to the environment. Grass and alfalfa crops reduce the drain volume and the N lost but when an alfalfa crop is broken it can release a lot of nitrogn. The 4Rs of nutrient stewardship (right source, right rate, right time and right place) come into play but rate is the big one. Porking on too much nitrogen is bad news.

In areas with warmer winters the ground does not freeze as much and winter rains can be a big part of the loss of N to drains. Mineralized N is an important source of loss.

The lesson for Western Canada

Our situation is very much different than the corn and soybean areas of the American Midwest. But as we start tile draining it is important to monitor what is happening with nutrient loss. It is better that we do it ourselves rather than wait until someone else does.

Monitoring is not given the attention it deserves. How can we know the impact of a farm management practice on our environment if we do not measure it? Too much of current research is of the short-term “quick fix” variety.

And, we can get on with a simple test to measure the N that will be mineralized during the growing season and use the results in deciding N fertilizer rates. Some work is now in progress and I hope there is a practical test soon.

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One option to consider is banding N fertilizer in late fall. But keep in mind that fall N application can range from very effective to very disappointing. Effectiveness depends on environmental conditions after application including soil moisture and temperature.

The products

The two best fertilizers for fall application are urea 46-0-0 CO(NH2)2 and anhydrous ammonia 82-0-0 NH3. When urea or anhydrous ammonia are banded into moist soil, both convert to ammonium NH4+. Ammonium is positively charged and is relatively immobile in soil and will not leach under wet conditions. In warm, moist soil, specific bacteria will convert ammonium to nitrate [NO3-] over a several week period. This process is called nitrification.

Nitrate is negatively charged, is mobile in soil and will leach with excess precipitation, particularly in sandy soils and can be loss to denitrification (gaseous loss of N in very, wet soil).

Banding ammonia or urea creates an environment within the band that slows the activity of soil bacteria that convert ammonium to nitrate, delaying nitrification. When urea or anhydrous ammonia are banded in late fall after the soils have cooled in temperatures less than 5 C to 7 C and micro-organism activity has slowed, most of the fertilizer N will be remain in the ammonium form over winter until the soil warms up in the spring. The ammonium form is relatively stable and won’t leach or denitrify.

If urea is broadcast and incorporated or banded in early fall when soils are still warm and moist, much of the ammonium can potentially be converted to nitrate before freeze-up. Excess precipitation in late fall or spring could then cause the nitrate to leach below the crop root zone, particularly in sandy soils or be lost due to denitrification. The denitrification process occurs when N fertilizer has converted to nitrate, soil conditions become very wet or saturated after snow melt in spring or due to heavy precipitation events. Soil N is lost when soil microorganisms in anaerobic conditions (very wet soil without oxygen) convert nitrate-N to nitrous oxide — a gaseous form of N that is lost to the atmosphere.

All soil types and regions of the Prairies are susceptible to losses of fall-applied N fertilizer. However, the risk of N loss is highest in regions with moister climates when soils can be very wet, such as the black and gray soil zones, and risk is lowest in regions that tend to be drier, such as the brown and dark brown soil zones.

Alberta research has shown that nitrate losses through denitrification in drier regions are usually low, and fall-banded N is usually equally effective to spring-banded N. But if spring wet conditions occur, N losses can still be high even in low risk regions, after heavy precipitation events. Each fall, a farmer must look at specific local environment conditions to weigh the risks versus benefits of fall fertilizer application.

Some issues to consider:

• Late fall-banded N can be as effective as spring banded N, if there is no extended period of very wet or saturated soil conditions in the spring.
• Early fall application of N fertilizer has a greater chance of converting to nitrate-N before freeze-up and would be more susceptible to N loss in the spring.
• Fall-banded N can be more effective than spring-banded N when springtime seedbed moisture is limited, and spring banding would dry out the seed-bed.
• Fall-banded N can be less effective than spring-banded N when spring moisture is wet for extended periods.
• Fall fertilization shifts workload from the hectic spring to the fall. This can increase spring seeding operation efficiency.
• Nitrogen fertilizer prices tend to be lower in the fall than in the spring, providing an economic advantage with fall versus spring fertilization.

It is wise to get opinions from soil and crop experts in your region including your fertilizer dealer, industry agronomist and government agronomist to consider all the pros and cons of fall fertilizing before you make your final decision.

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