Objectively Measuring Products and Practices with the SWAT ECOSYSTEM 

In agriculture, farmers and agronomists are inundated with products and practices promising to rejuvenate soil, enhance crop health, and boost yields. These claims are often accompanied by side-by-side photos of plants or roots, showcasing dramatic differences in size, color, or vigor. While compelling at first glance, these images frequently lack any scientific rigour as they are often cherry-picked examples from unknown conditions that may not represent the broader field or treatment areas. 
 
To make informed decisions, it’s crucial to evaluate these claims objectively. As agronomists, our role is to cut through the noise and provide measurable insights into how products or practices impact crop performance. While the SWAT ECOSYSTEM offers a suite of tools designed to enable precise, evidence-based evaluations, there are also other valuable resources available that can help bring clarity to these assessments, ensuring farmers and agronomists make decisions backed by reliable data. 
 
Consistency in Side-by-Side Comparisons 
Before diving into specific tools, it’s worth noting that any side-by-side comparisons must start with consistent sampling. At a minimum, plants should be chosen from the same SWAT zone—areas defined by soil, water, and topography characteristics. For instance, selecting samples from a Zone 5 (a mid-slope) ensures that the plants are growing in similar environmental conditions, reducing variability unrelated to the product or practice being tested. This basic principle is the foundation for fair and objective assessment.

Yield Analysis with the Yield Potential Program (YPP)
One of the most reliable indicators of success is yield. By using yield maps, farmers and agronomists gain an objective view of crop performance across an entire field. The SWAT MAPS Yield Potential Program (YPP) enhances this process by breaking down yield data by SWAT zones and further, into treatment areas if applicable.

This functionality allows farmers to identify how a product or practice performs under various conditions within the same field. For example, a fertilizer might show a higher yield response in an upper landscape position or SWAT zone 1-4 for example, while its impact diminishes in wetter, depressional areas. Best practices for such trials include replicating treatments across multiple zones to minimize bias and improve reliability.

Assessing Crop Growth with SWAT CAM
SWAT CAM, a sprayer-mounted field imaging system, offers another layer of insight. It provides high-resolution images of the field after each sprayer pass, enabling agronomists to assess crop growth and plant stands with precision.

SWAT CAM can be particularly useful for visualizing treatment effects very early in season. The system creates maps of plant stands and crop coverage, with the added ability to zoom in on individual image points. This tool empowers farmers to make informed decisions by monitoring how products or practices influence crops throughout the growing season. Instead of relying solely on end-of-season yield data, SWAT CAM provides real-time feedback on plant health and uniformity.

Leveraging Other Tools for Objective Insights
In addition to YPP and SWAT CAM, several complementary tools can help refine treatment evaluations:

Satellite Imagery: Platforms like the Copernicus Browser offer weekly biomass imagery, allowing you to monitor growth differences throughout the season. While cloud cover or smoke can interfere with acquiring useful images, this is an excellent resource for spotting trends across large areas.

Comparative Tissue Testing: Tissue testing from treated and untreated areas within the same SWAT zone provides insights into nutrient uptake and plant health. This can often explain yield differences observed in the field.

Feel Confident in Your Decision Making
As an industry, we can do better than subjective side-by-side photos as evidence of product efficacy. By leveraging tools in the SWAT ECOSYSTEM—YPP for yield analysis, SWAT CAM for growth monitoring, and satellite imagery for seasonal trends—we can move toward more objective, data-driven evaluations. Many of these tools are readily accessible, cost-effective, and easy to implement, offering a deeper understanding of soil, crop, and yield variability. If you're ready to elevate your approach to assessing products and practices, start with the base layer for all SWAT ECOSYSTEM tools.

Interested in these tools? Get in touch with your SWAT MAPS agronomist today.

Using SWAT MAPS to optimize fertility recommendations, reduce crop Inputs, and save $$$

Sean Barath
Precision Agronomist
sean.barath@swatmaps.com

Introduction
Every fertilizer recommendation should start with soil test data. Without soil test data you would basically be making blind recommendations, based on yield goals and crop uptake/removal tables. This is not an ideal method of nutrient planning as you could either over or under apply certain nutrients.

Soil Testing
Composite soil testing (Table 1) can be a good starting point for making fertilizer recommendations for flat rate applications; however, it only captures soil nutrient levels in the mid-slope areas of fields, leaving out important information on soil nutrient levels in depressions or hilltops. Implementing zone-based soil sampling (Table 2) along with the use of SWAT MAPS variable rate seed and fertilizer can help producers get their best ROI on inputs and save money.

Table 1. Example of composite soil sampling test results.

Table 2. Example of zone-based soil sampling test results.

Right away, the zone soil test results in Table 2 show some potential cut back on nitrogen and phosphorus rates in upper and lower SWAT MAPS zones. Zones 1-2 are hilltops where the yield is most limited by low moisture levels, whereas zones 7-10 start getting into yield-limiting levels of salinity. There are already higher soil nitrate and phosphate levels in these areas which will also influence the recommendation for these zones. The zone soil test also sheds some light on other soil factors that the composite sample does not show. The pH levels are elevated in zones 1-2 and 7-10, OM differences between zones are significant and sulfur and zinc levels in zone 1-4 are lower.

Fertility Recommendations

The process of making fertility recommendations based on a SWAT MAP is simply not a button to hit that gives a recommendation. Agronomists are in contact with the farmer early in the fall to discuss any fall fertilizer passes, and then again in the winter for spring plans. In some cases, the grower has a set fertilizer budget to work with, while other growers want a fertility plan more aligned with yield goals and soil test results. Once agronomists have the grower's intended fertility plan, VR recommendations can begin.

Soil test results (Table 2) are the main tool to determine crop demand for a certain yield goal. The soil test is also very useful in determining the soil N supply, including left-over nitrates, organic matter credits, and N credits for cases like previous pulse crops, broken up hay/alfalfa land or previous manure applications. A critical soil test N level of 20 lbs/ac is used. If levels are below this threshold at year end, the crop was potentially starved. If levels are higher than 20 lbs/ac, the crop was supplied with too much N, other factors limited yield and nutrient uptake, or the soil mineralized more nitrate in season that the crop didn't use. When making recommendations, the crop is supplied with enough N for the yield goal while maintaining the 20 lb/ac level at year end. N credits can be tricky as there aren't absolute numbers for the mineralization rate and amount of N coming from the organic matter, pulse crop residue, old hay residue, or manure applications. Organic matter credits can range from 6-8 lbs of N per % OM but can be unpredictable in terms of the above-mentioned practices. When making zone-based recommendations with N credits, the size of credit given can also be based on the landscape position of the field. Zones 1-2 usually have the lowest N credit per % OM as these areas tend to be driest, resulting in less mineralization. In Zones 3-8, credits gradually increase due to higher mineralization potential in lower landscape areas as soil moisture and organic matter content increases. Zones 9-10 can have the highest N credit unless poor health limits microbial activity.

Figure 1. Nitrogen Recommendation for a 45 bu/ac average canola crop.

The example SWAT MAPS Field in Figure 1 has soil nitrate levels of 15 lbs to 104 lbs. The zone trend is common, especially after drought years where the zone 1-2's (hills) and zone 7-10's (saline areas) both have high soil nitrate levels where the crop use was low. The organic matter levels range from 4.6 to 6%. The average canola yield goal for this field is 45 bu/ac; however, yield goals per zone do vary based on zone characteristics that limit yield potential. Canola is a heavy user of N, using roughly 3 lbs N per bushel of grain produced. Using the yield goals from Figure 1 would result in crop demand ranging from 105 lbs actual N to 150 lbs actual N. Crop demand is an easy starting point to begin making the recommendation. Total soil supply includes residual nitrates plus N credits from organic matter, minus any losses that may happen and minus the 20 lb/ac year end critical level. Losses are hard to predict but N losses in lower, saturated areas within a field due to denitrification are more likely to happen. There can be leaching losses in sandy areas as well with very wet conditions. Once soil supply is determined, this amount is subtracted from crop demand and the remaining fertilizer requirements are made into a VR report.

In a SWAT MAPS recommendation for P, 15 ppm Olden-P generally is the critical level. Less than 15 ppm is low and zone(s) testing low will receive higher P rates to increase the soil test P level to above 15 ppm. If the soil test level is higher than 15 ppm, maintenance rates are applied to the zone(s) to maintain the soil test levels above 15 ppm. If soil test levels are high, to a point where they become an environmental concern, lower P rates are applied to allow the crop to mine the excess P from the soil. In the SWAT MAPS field example, the soil test in Table 2 shows zones 3-6 are well below the critical level of 15 ppm. These areas are the focus for the VR phosphate application. Zones 1-2 and 7-10 soil test levels are above the critical level and will receive maintenance rates. Depending on yield limiting factors, lower P rates may be applied to allow the crop to mine from the soil. Saline areas and fields that have had excessive manure applications in the past are some examples of where mining soil P instead of maintaining the levels would occur. Table 3 has recommended application rates from AGVISE Laboratories for P based on soil test levels and yield goals. Canola is a heavy user of P, removing roughly 0.9 lbs of P2O5 per bushel of canola grown and this needs to be taken into consideration when making P recommendations for canola. The soil test results for the example field in Figure 2 are showing soil P levels down to 8 ppm. According to this recommendation chart and the yield goal, it would need to be 40-45 lbs of actual P2O5 just to maintain this soil test level; however, applying higher rates to build the soil P level is a good idea.

Table 3. Phosphorus fertilizer recommendation guide from Agvise Laboratories.

Figure 2 shows an example VR report of the N & P recommendations for the example field. As you can see, the fertility rates do vary significantly depending on zones, soil test data and the overall crop demand.

Figure 2. Example VR report for SWAT MAPS field.

Variable rate vs. Flat Rate Applications
You might be wondering how variable rate will give you the best ROI on your inputs and possibly save you some money. The soil test results from Table 1 and Table 2 would result in very different fertilizer applications. A recommendation based on the composite soil test would result in high application rates being applied to the whole field. The zone-based soil test is telling a different story, where there is opportunity to rely on residual N and P levels to supply the crop with part of the fertility demand along with accounting for yield limiting factors like the salinity in Zones 7-10. In Figures 3 and 4, variable rate vs flat rate urea comparison shows how effective SWAT MAPS can be at saving product from over application in areas of the field that don't need the extra fertility.

Figure 3. Urea VR vs FR comparison for the example field.
Figure 4. Phosphorus VR vs. FR comparison for the example field.

Conclusion
Composite soil testing is a good start when making fertilizer recommendations; however, this sampling method misses important details within areas of a field like nutrient levels, pH differences, salinity, organic matter, etc. Zone-based soil sampling and SWAT MAPS Variable Rate is the most effective way to capture all the variability within a field. In the variable rate vs. flat rate example, the grower would save 37,875 lbs of urea and 19,144 lbs of MAP just by using SWAT MAPS on this field. That is a large amount of product saved and can result in product reallocated to other fields or saved money that can be invested into other areas on the farm. Talk to your SWAT MAPS service provider about how they can help you get the best return on your crop inputs and save money with SWAT MAPS Variable Rate.