Although the prairies are known for having the largest reserves of potash in the world, there are some areas with soils that have relatively low background potassium (K) levels — particularly in the black and dark grey soil zones of Canada that span northern Alberta, Saskatchewan and into Manitoba. In spring 2023, many of these areas are where we saw higher than normal temperatures coupled with humidity and adequate moisture. This created greenhouse-like growing conditions, making crops’ demand for nutrients high, resulting in more visual nutrient deficiencies than we might normally see, particularly K deficiency in cereal crops. 

Symptoms

There are many possible symptoms of K deficiency which can make diagnosis difficult. Looking at soil tests by SWAT zone combined with a comparative tissue test are often required to confirm deficiency. Symptoms include:

• Yellowing of the oldest leaves
• Poorly developed roots
• Weak stems
• Poor water use efficiency
• Smaller seeds
• Poor N uptake

The most obvious and common deficiency symptom is yellowing of the oldest leaf that starts at the tip and progresses toward the base of the plant. These plants also tend to be stunted and have less biomass overall. Another common observation in fields displaying K deficiency is the presence of green, healthy strips where there was heavy straw or swaths —particularly in canola stubble — from previous years as K is the only nutrient that can be added directly back into the soil and is readily available by leaching through straw. 

Where to look

In the higher rainfall areas of the black and dark grey soil zones, soil K distribution tends to be predictable in relation to SWAT Zones. Soil K levels tend to be lower in upper landscape positions (zones 1-4) and higher in lower landscape positions (zones 7-10). SWAT Zones 1-4 generally have lighter soil texture and are water shedding, which allows for the movement of K down-slope. Potassium levels can also be correlated with soil texture, where higher clay content and cation exchange capacity means more K is held to soil particles and is less prone to leaching. These are soil characteristics more often seen in SWAT Zones 7-10. Given the generally higher annual rainfall in these regions, in many instances yields might be highest in zones 1-4 resulting in the greatest rates of nutrient removal.  

Table 1. K trend by SWAT zone in the grey soil zone of NE SK.

Field Area	N	OM %	pH	P (Olsen-P)	K	S	Cl	Salinity
Zone 1,2	13	2.6	7.2	17	107	27	5	0.12
Zone 3,4	16	4.4	6.7	8	146	45	12	0.23
Zone 5,6	21	6.3	7.7	10	156	45	8	0.26
Zone 7,8	32	6.3	7.6	16	230	45	24	0.34
Zone 9,10	33	8.6	7.2	19	252	160	21	1.01

K Stratification

Nutrient stratification is a naturally occurring process. Roots take up moisture and nutrients from below the soil surface and relocate them to above ground plant tissue to then be laid back on the soil surface when the plant’s life cycle is over. This process continues to happen in agriculture but is accentuated by some farming practices. Minimum or no-till fertilizer practices typically result in fertilizer being placed somewhere in the top 0-2” of the soil surface; however, plants are taking up nutrients throughout the soil profile which are returned to the soil surface in the form of straw. So, with relatively immobile nutrients such as phosphorus (P) and K, these nutrients continue to become very stratified in the top couple inches of soil (Table 2). Broadcast applications of P and K further accentuate this occurrence.

Table 2. Soil test P and K at varying depths and from a 0 to 8” test depth, from the Black Soil Zone of Saskatchewan.

Soil Test Depth	P (Olsen-P, ppm)	K (ppm)
0-2”	16	299
2-4”	6	178
4-8”	2	159
0-8”	5	248

In Figure 1, deficiency symptoms seemed to skip several seed rows in this field. This is the result of a few openers of the drill seeding shallower and seedlings accessing K that was likely stratified from previous years’ broadcast potash applications and from long-term no-till farming practices. K deficiency was confirmed through tissue testing healthy versus unhealthy rows of plants.  

K Uptake and Removal by Crop Type

K requirements vary substantially based on crop type, (Table 3). Although some of the crop types listed below have high requirements for K such as peas and fava beans. Barley seems to be the most sensitive to K deficient soils and the crop type we see deficiency symptoms in the most often. 

Opportunities for Management with SWAT MAPS.

Understanding K allocation within your fields using SWAT MAPS allows for more precise management. SWAT MAPS allows you to take your existing fertilizer budget and allocate nutrients like K to areas that need it the most. That could be areas of the field that are testing deficient or areas of the field where you are most likely to see a response based on the soil properties mentioned above. ROI on applied potassium can be improved using SWAT MAPS, especially if doing applications in large quantities to build soil test levels. 

References

The need for potassium. (n.d.). Potassium fertilization in crop production. https://www.saskatchewan.ca/business/agriculture-natural-resources-and-industry/agribusiness-farmers-and-ranchers/crops-and-irrigation/soils-fertility-and-nutrients/potassium-fertilization-in-crop-pro

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Ethan Rheaume
Precision Agronomist

Variable rate technology is becoming more commonplace in the ag community, yet the adoption rate is still relatively slow. Some surveys suggest there is less than 10% adoption of variable rate by Canadian farmers. However, it’s possible that the adoption rate is about to grow exponentially in the coming years. Farmers are realizing that an effective variable rate program like SWAT MAPS is very important, especially now. Here are five reasons why. 

Optimize the Use of Inputs

These days, farm input prices are very high, so it is becoming even more critical to not waste them. Variable rate technology enables precise management of resources such as fertilizers, pesticides, and even irrigation water. By applying these inputs in varying amounts based on soil, water, and topography characteristics, farmers can optimize their resources (see Figure 1). This leads to increased efficiency, reduced waste, and cost savings, making it an essential tool for sustainable and environmentally friendly practices.

Evenness of Crop Maturity

Protecting the growing crop has never been more important. Variable rate seed and fertilizer  will promote even crop staging and maturity (Figure 2). Achieving a proper plant stand will minimize excess tillers or branching that delays maturity and causes uneven crop staging throughout the season. This can significantly improve control of diseases such as fusarium head blight and hasten maturity in low areas that are normally too delayed to harvest when the rest of the field is ready. This has very high value for all farmers but especially for seed growers who need seed viability or can't use glyphosate as a preharvest aid. Not to mention the value of getting the crop off before that storm hits!

Enhanced Crop Productivity 

Optimizing yield wherever possible is crucial. When using a fixed rate application of inputs, farmers are forced to use field average rates. For example, they can't optimize yields in those areas that would benefit from more fertilizer because other areas in that same field may be prone to lodging and would therefore see a negative impact from more fertilizer.

Alternatively, farmers using variable rate technology can increase fertilizer rates in areas that would benefit from it and decrease it (or even shut it off completely) in areas where more fertilizer would be detrimental. By providing the right amount of nutrients, and other inputs, to each part of the field, this technology helps optimize crop growth and yield, which can therefore result in improved productivity and profitability for farmers.

Site-Specific Management 

Especially these days, farmers must reduce costs whenever they can. Fields often exhibit spatial variability caused by differences in soil properties, topography, and other factors. SWAT MAPS help farmers address these variations by creating management zones and treating each zone differently. Perhaps there are only certain zones within a field that would benefit from application of a micronutrient. Since that micronutrient may not provide an economically significant benefit to the rest of the field, variable rate prescriptions can be made to apply the product only in the areas where it is required. This approach can dramatically reduce costs and increase ROI since unnecessary application of product in other areas of the field can be eliminated.

Environmental Sustainability

Proper use of variable rate technology plays a vital role in sustainable agriculture. By precisely targeting inputs, it reduces the potential for over-application of fertilizers and chemicals, minimizing the risk of environmental pollution and nutrient runoff into water bodies. Additionally, variable rate can even promote responsible water management by optimizing irrigation practices, reducing water usage, and minimizing soil erosion.

In fact, here in Canada, substantial government funding is now in place through the On Farm Climate Action Fund (OFCAF) to help farmers farm even more sustainably. There are various organizations that farmers can apply for funding through. Below are a few of them:

• The Canola Council of Canada - 4R Advantage program
• Manitoba (and Saskatchewan) Association of Watersheds - Prairie Watershed Climate Program
• Results Driven Agriculture Research - RDAR

There are many other reasons why variable rate technology is important, but essentially, when a great variable rate program is combined with great agronomy, it offers better resource efficiency, increased productivity, better crop management, and environmental sustainability. Furthermore, right now our government is willing to subsidize farmers who want to make variable rate application a part of their operation. There is no better time than now to get started.

If you would like to further discuss how variable rate might benefit your farm specifically, please connect with us at support@swatmaps.com. Or you can find more information elsewhere on our website.

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Chris Hawkins
Director of Sales – Farmer Services

Trials are an important part of our learning about how different treatments benefit each SWAT ZONE.  Whether it is a replicated trial, a casual strip trial or a field split in half, collecting the data at harvest time is key for future decision making.  

About Our Process

The SWAT MAP Yield Potential team approaches trial data differently than processing yield on a field scale.  First, because we are dealing with smaller areas, we use a much higher resolution map.  Then, we manually clean the raw point data to ensure the maximum amount of quality data is preserved.  Data points too close to trial edges are removed to reduce the effect of any overlap between treatments.  Headlands and passes around sloughs or obstacles are also removed.

Best Practices for Harvest

The most crucial part of harvesting trials is direction.  Harvesting along the same direction as the trial strips will preserve as much of the data as possible and make those results most accurate.  Because we clip the data close to trial boundaries, harvesting at 90 or 45 degree angles will reduce the usable data by 50-70%.  

Direction is so important that our GIS team will design trial strips to match what farmers intend to do.  We implement square blocks instead of strips for farms that harvest on 45 degree angles.

When possible, use the same combine to harvest the trials and a minimum of 2 surrounding passes.  This way we can rule out machine discrepancies in the data and have enough data around the trial to use as a control.  For large trials where a field is split in half, try to run your combines side by side so an equal area is covered by each machine in each treatment area.  The same principles also apply to swathing.

Calibration

Trials often have a wide range of yields between treatments and different SWAT ZONES.  To accurately capture this, it is important to calibrate your combines at different flow rates to ensure the yield monitor is reading correctly regardless of the crop conditions.  

When using a weigh wagon, it is important to keep accurate, easy to understand records of the weights and what is being weighed. Also ensure the units of measurement are clear. Measuring bulk density (bushel weights) is also helpful. 

Results

The cleaned data points are sorted by SWAT ZONE and analyzed for statistical significance.  This is done by using each data point in the trial and zone area, not just by average yield.  This method takes into consideration the variability that may exist in each trial.  

Our findings are presented to the farm in graph and chart format.  The agronomist will include an interpretation of results along with recommendations for future use.

Considering a Field Trial?

We are excited about learning how products and treatments interact with each SWAT ZONE.  Talk to your SWAT MAPS service provider about requirements and funding opportunities.  

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Danielle Epp
Yield Potential Manager

Crop lodging is a significant problem that leads to decreased yields, deterioration in seed quality, and decreased harvestability ease. Crop establishment that reaches target plants/sq ft and proper nitrogen  management contribute to decreased lodging risk later in the growing season.

Early in the growing season it is common to see abundant moisture. Under wet soil conditions crops grow poorly developed shallow root systems. Areas of a field that are typically water holding with excess moisture are SWAT Zones 7-10. These are the areas that you will notice lodging later in the season because the crop has a poorly developed root system with excessive above ground growth. An established crop stand will use soil water more efficiently. SWAT MAPS can aid in establishing a good crop stand by using variable rate technology to apply seeding rates. When variable rate seed is practiced, seed rates are increased in higher mortality zones, which commonly includes Zones 7-10. Increasing seeding rates in these high mortality zones improves the crop plant stand. Variable rate seed applications aid to target plants/sq ft evenly throughout zones in a field. Reaching plant stand targets reduces excessive tillering that shallow root systems can not support later in the growing season. 

SWAT MAPS have proven that there is significant organic matter content variations throughout zones. The more organic matter in a soil the more nitrogen mineralization that will occur throughout the year. During the mapping and soil sampling process, SWAT MAPS identifies the areas that are lower and higher in organic matter. We know that  excessive plant growth follows excessive nitrogen application which leads to lodging. We can variable rate nitrogen applications based on the knowledge of residual nitrogen levels left in the soil from the year prior while taking into consideration the amount that the soil will mineralize throughout differrent zones. Utilizing variable rate nitrogen applications will prevent lodging by ensuring the crop does not have excessive nitrogen in the soil and this practice will also aid in even crop  maturity. 

SWAT MAPS has the capability to also create variable rate spray applications. In the case of preventing lodging, we can variable rate apply plant growth  regulators (PGRs). PGRs promote stronger stems to mitigate lodging. Fields that are a fit would include those with poor burned out crop zones due to drought or poor drowned out crop zones due to excessive moisture all season long.

SWAT MAPS can reduce lodging risk by providing the technology to variable rate seed, fertilizer and spray applications. These applications will enhance plant establishment to reach target plant populations throughout zones in a field. The applications will also provide nitrogen management throughout zones. SWAT MAPS will not only reduce lodging risks but will also even maturity for harvest profit and easeability. 

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Rachelle Murrison
Precision Agronomist