Alternative Way to Apply Fertilizers Based on Field Map Analysis
Heterogeneous field example
Usevalad Henin
Usevalad is an expert in GIS and agricultural chemistry. He has been developing precision farming tools since 2013. He is also the co-founder of OneSoil.
In our previous article, we looked at how to perform a soil analysis just before applying fertilizers. We reviewed different soil sampling methods and modeled nutrients distribution maps. All of this took place in Ukraine in a highly heterogeneous field. We teamed up with Frendt for the project. It turned out that, in this kind of field, you can only get reliable soil analysis results if you use a very dense sample grid. That means that with an average cost of $ 20-50 per sample, a soil analysis would be very expensive. That raises the question: is there another way to calculate the fertilizer needed for variable-rate application?
In our previous article, we looked at how to perform a soil analysis just before applying fertilizers. We reviewed different soil sampling methods and modeled nutrients distribution maps. All of this took place in Ukraine in a highly heterogeneous field. We teamed up with Frendt for the project. It turned out that, in this kind of field, you can only get reliable soil analysis results if you use a very dense sample grid. That means that with an average cost of $ 20-50 per sample, a soil analysis would be very expensive. That raises the question: is there another way to calculate the fertilizer needed for variable-rate application?
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And the good news is, there is! We suggest applying fertilizers based on productivity zones instead of nutrient distribution maps. In this article, we’ll explain what it means and why it makes sense.
Why you need to apply fertilizer
Let’s start with the basics. Fertilizers are needed to increase yields and to support plant growth and development.
Factors that typically limit the yield
There is no one-size-fits-all answer. Unfortunately, nature usually doesn't offer ideal conditions for growing crops.
Crop yield is sometimes affected by a sudden drought or by a storm in the middle of the season. Sometimes the organic nutrient content or a lack of phosphorus in the soil can be the culprit for low yield. It's hard to factor everything in. What can you do?
Agricultural chemistry has a notion called the 'limiting factor'. This is the factor that deviates the most from the optimal value. According to Liebig's Law of the Minimum, this factor limits plant development the most at a specific moment in time.
If we base our theory solely on soil chemical properties for variable-rate fertilizer application, we might assume that the limiting factor is always the nutrient content. But many other factors, such as moisture distribution on the field, may affect the yield. Moreover, if we're dealing with a heterogeneous field, almost each individual area may have its own limiting factor.
Crop yield is sometimes affected by a sudden drought or by a storm in the middle of the season. Sometimes the organic nutrient content or a lack of phosphorus in the soil can be the culprit for low yield. It's hard to factor everything in. What can you do?
Agricultural chemistry has a notion called the 'limiting factor'. This is the factor that deviates the most from the optimal value. According to Liebig's Law of the Minimum, this factor limits plant development the most at a specific moment in time.
If we base our theory solely on soil chemical properties for variable-rate fertilizer application, we might assume that the limiting factor is always the nutrient content. But many other factors, such as moisture distribution on the field, may affect the yield. Moreover, if we're dealing with a heterogeneous field, almost each individual area may have its own limiting factor.
How to identify the limiting factor
1. Determine the productivity zones in the field
Productivity zones show the fertility level in different areas of the field. They're based on yield and vegetation data. If we know the yield, we can identify the areas that had below-average metrics. That means that these areas have limiting factors.
How do you do it? You can define productivity zones for free in the OneSoil web app. The app builds the zones according to vegetation and relative yield for the last four years calculated by our algorithm based on the satellite images. All you need to do is sign up, go to the 'Fertilizers' section, and select your field. You'll then see the productivity zone map.
Productivity zones show the fertility level in different areas of the field. They're based on yield and vegetation data. If we know the yield, we can identify the areas that had below-average metrics. That means that these areas have limiting factors.
How do you do it? You can define productivity zones for free in the OneSoil web app. The app builds the zones according to vegetation and relative yield for the last four years calculated by our algorithm based on the satellite images. All you need to do is sign up, go to the 'Fertilizers' section, and select your field. You'll then see the productivity zone map.
Cost: free
2. Compare productivity zones and terrain
If the productivity zone map looks like the relief map, the relief affects the chemical and physical properties and the moisture distribution on the field. The moisture, in turn, affects the yield. Most of the time, there's nothing we can do about it. If moisture distribution is the only limiting factor, feel free to start applying fertilizer.
How do you do it? You can usually download the relief map from your equipment's onboard computer. Render it in the OneSoil web app and move on to analysis. This is how we always work when we conduct experiments.
If the productivity zone map looks like the relief map, the relief affects the chemical and physical properties and the moisture distribution on the field. The moisture, in turn, affects the yield. Most of the time, there's nothing we can do about it. If moisture distribution is the only limiting factor, feel free to start applying fertilizer.
How do you do it? You can usually download the relief map from your equipment's onboard computer. Render it in the OneSoil web app and move on to analysis. This is how we always work when we conduct experiments.
Cost: free
A slope map for a field in Ukraine with the productivity map superimposed. High slopes overlapped with low-productivity zones. After reviewing these areas, I discovered soil erosion
3. Compare productivity zones and soil brightness
If productivity zones aren't linked to the terrain, take a look at soil brightness. If the productivity zone map looks similar to the soil brightness map, its humus content may be what's affecting the yield.
How do you do it? To analyze soil brightness, look at an image of the soil after it was tilled and without any plant matter on its surface. It's easiest to do right after sowing. You can download this image from a dedicated website by Sentinel. Sign up, select your region on the map, and download the image in B08 format. This is an image in the near-infrared spectrum. After that, upload the image to any GIS software, increase the contrast, and start your analysis.
If productivity zones aren't linked to the terrain, take a look at soil brightness. If the productivity zone map looks similar to the soil brightness map, its humus content may be what's affecting the yield.
How do you do it? To analyze soil brightness, look at an image of the soil after it was tilled and without any plant matter on its surface. It's easiest to do right after sowing. You can download this image from a dedicated website by Sentinel. Sign up, select your region on the map, and download the image in B08 format. This is an image in the near-infrared spectrum. After that, upload the image to any GIS software, increase the contrast, and start your analysis.
Cost: free
The map shows that the soil is lighter in areas where the slope is around 3 degrees. These same areas overlap with the low-productivity zone. That means productivity is affected by organic nutrient content
4. Check the soil acidity
If the soil brightness, terrain, and productivity are not connected, look at soil acidity. You can do it at a lab or using a pH meter.
It's important to take care of any acidity issues before applying fertilizer. If you don't do that, the plants may simply not absorb the fertilizer. For example, in low acidity, phosphorus can be unavailable to plants.
Analyze the phosphorus, potassium, and other macronutrient and micronutrient content only after you've assessed the field and made sure that neither the terrain nor the organic nutrient content is limiting the yield and that acidity levels are acceptable.
If the soil brightness, terrain, and productivity are not connected, look at soil acidity. You can do it at a lab or using a pH meter.
It's important to take care of any acidity issues before applying fertilizer. If you don't do that, the plants may simply not absorb the fertilizer. For example, in low acidity, phosphorus can be unavailable to plants.
Analyze the phosphorus, potassium, and other macronutrient and micronutrient content only after you've assessed the field and made sure that neither the terrain nor the organic nutrient content is limiting the yield and that acidity levels are acceptable.
Cost: $20-50 per sample
How to apply fertilizers based on productivity zones
The process is simple:
1
Identify productivity zones.
2
Determine what the limiting factor is and eliminate it, if possible.
3
Calculate the fertilizer rate for every productivity zone.
When calculating, take into account the planned yield and the fact that nutrient removal in zones with low and high productivity will be different. The parts with high crop yield have a higher level of nutrient removal, while areas with low crop yield will have lower levels.
This is how you can calculate the phosphorus and potassium fertilizer rates for free using OneSoil. We'll automatically calculate soil nutrient removal for every zone and determine the fertilizer rate.
This is how you can calculate the phosphorus and potassium fertilizer rates for free using OneSoil. We'll automatically calculate soil nutrient removal for every zone and determine the fertilizer rate.
Things to remember
If you want to maximize your field's potential and increase yields using fertilizers, we recommend you start by analyzing the productivity zones. After that, find the limiting factor, eliminate it if you can, and apply fertilizer.
Even the most precise soil nutrient analysis can amount to a hill of beans (and not in a good way) if the nutrient content is not the limiting factor.
You can use the OneSoil app to identify productivity zones. You can also automatically calculate the phosphorus and potassium fertilizer rates by productivity zone and build a prescription map for your equipment. And it's all for free.
Even the most precise soil nutrient analysis can amount to a hill of beans (and not in a good way) if the nutrient content is not the limiting factor.
You can use the OneSoil app to identify productivity zones. You can also automatically calculate the phosphorus and potassium fertilizer rates by productivity zone and build a prescription map for your equipment. And it's all for free.
Things to remember
If you want to maximize your field's potential and increase yields using fertilizers, we recommend you start by analyzing the productivity zones. After that, find the limiting factor, eliminate it if you can, and apply fertilizer.
Even the most precise soil nutrient analysis can amount to a hill of beans (and not in a good way) if the nutrient content is not the limiting factor.
You can use the OneSoil app to identify productivity zones. You can also automatically calculate the phosphorus and potassium fertilizer rates by productivity zone and build a prescription map for your equipment. And it's all for free.
Even the most precise soil nutrient analysis can amount to a hill of beans (and not in a good way) if the nutrient content is not the limiting factor.
You can use the OneSoil app to identify productivity zones. You can also automatically calculate the phosphorus and potassium fertilizer rates by productivity zone and build a prescription map for your equipment. And it's all for free.
Usevalad Henin applied fertilizer without soil analysis
Map created by Nastia Zenovich
Text edited by Tanya Kavalchuk
Article layout by Anton Sidorov
Map created by Nastia Zenovich
Text edited by Tanya Kavalchuk
Article layout by Anton Sidorov
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