In the last article, we discussed how yield zones work and how they can improve your variable-rate programs. But one thing that still needs to be addressed is the data sources you will use and how you will gather that data to create these yield zones. There are a few different data sources and data gathering methods you may consider when creating yield zones, and we will address those in this article.
CEC
One simple way to make yield zones is to simply use the CEC levels from your typical gridded soil test. CEC stands for Cation Exchange Capacity and is a measure of how many cations can be retained on soil particle surfaces. Basically, it tells you what soil texture you are working with. There are several drawbacks to relying on this method. For starters, this method only shows what the soil texture is at the point taken by the sampler, which is about every 2.5 acres on average. This means that you are only getting a reading on a very small point every 2.5 acres, so a map made based on that small amount of information hardly tells the whole story. Also, it is worth mentioning that the soil probe only takes a sample from approximately 9” deep, which is not very deep when considering the water-holding capacity of the soil. This method should only be used if you are very constrained on both time and money due to its lack of accuracy.
EC Data
Using EC data to make yield zones is a method that has gained some popularity in the last decade. Measuring the EC (electrical conductivity) of the soil can show you how quickly electricity can pass through the soil, giving you an idea of the soil texture you are working with. An EC sample is usually taken with a machine like the Veris Machine. This machine, pulled behind a farm vehicle or tractor, will send electrical pulses between its coulters and measure how long it takes for the pulse to travel between them. It takes both a shallow and deep measurement, where the shallow measurements reach 12” and the deep reaches 36”. It then uses GPS to create a map of this reading. Unlike the CEC method, this method uses data gathered from the whole field, but there are still a few drawbacks.
One major drawback is that the numerical system used to map EC data is relative to the field you are in. This means that if a field has very little clay content, the veris machine will still map the highs and lows of EC for that field, which can be confusing when the final analysis comes. You could have a field with very little clay content, meaning that the EC may be mapping a portion of the field in a way that illustrates it as a low-yielding area when it is a high-yielding area. The remedy to this issue is to ground truth the field, meaning that you would travel to specific points on the EC map created to identify what soil texture the EC numbers are correlated with. Then you can determine which numbers are high-yielding and which are low-yielding.
Another drawback is the short testing window. You cannot run a Veris Machine over frozen ground, overly wet ground, or overly dry ground. The machine cannot penetrate frozen soil to the point it needs to take a measurement. If the soil is too wet, then the soil will stick to the coulters and throw off the reading. If the soil is too dry, then there isn’t enough moisture in the ground for the electric pulse to travel through and show enough variability in the readings to determine differences in soil texture. You have to hit it just right, which can be difficult in the off-season between harvest and planting the following year.
In short, the EC or Veris Machine method of data-gathering to create a yield zone is much better than relying solely on CEC, but is debatably not the most accurate option available. With the readings being relative from field to field and not having a true objective standard to what the data gathered stands for, it would be difficult (not to mention time consuming) to determine what yield goals would be appropriate for each yield zone with EC data alone.
Field Health Imagery
Field health imagery has become very popular lately, and for good reason. Through satellite and drone imagery, you can now see how healthy your fields look throughout the growing season. Many field health satellite imagery services give you updates once or twice per week, which means that you can accurately track your crop’s response to events throughout the summer. If you have access to a drone, you can fly them whenever you wish. Drones also take some very detailed pictures compared to satellites.
How does all of this factor into creating yield zones? You can track how well your crops do in certain areas in your field over a span of multiple seasons, which is basically the essence of making a yield zone. Pro tip: if you have satellite imagery of a field during a period of drought-stress, then that image will be very effective in identifying your most profitable areas. The areas of the field that did the best under stress are probably working with the best soil if all other factors are held equal.
There are a few drawbacks to using field health imagery as well, unfortunately. Firstly, the quality of the image must come into question. While images may be taken via satellite twice per week, there is still a decent chance that they were taken on a cloudy day. The dice is being rolled every picture taken, so in the end there may not be an over-abundance of usable pictures throughout a growing season due to cloud coverage. You can mitigate this by using a drone-flying service, but that can be expensive and time-consuming, depending on the service.
Another drawback of field health imagery is that the data gathered through this method does not help to estimate yield. Like EC data, it maps your highest-potential soil relative to your worst but doesn’t help you to decide how many bushels per acre to shoot for in any given area. You will have to refer to your yield data to come up with a solid yield goal.
Yield Data
This brings us to what is possibly the most reliable data source for creating yield zones, and that is simply yield data. If you have a yield monitor and have been saving your yield data from each year, then you have set yourself up nicely to make accurate, data-backed yield zones and yield goals. Using multiple years of yield data averaged together can show you a nice trend of high-yielding areas vs low-yielding areas of your fields. Not only that, but you can also use this yield data as an objective standard across your entire farming operation and not just one field at a time. This separates yield data from EC and satellite imagery.
Another big advantage of making yield zones from yield data is that it somewhat accounts for outlying factors. You cannot predict what will happen in any given season. There are so many things that can go wrong and take away from a good yield, and there is a new set of factors that affect your yield presented every season. This is why yield data averaged over several years can be very useful. It’s a “climate” vs “weather” scenario. If we know the trends shown over a large sample size of yield, then we can bet along the lines of that trend instead of trying to predict the weather and guess what will happen this year.
As with other data sources for creating yield zones, there are some drawbacks to yield data as well. For starters, statistical outliers do happen, so if you don’t have a large sample size, then your data might be skewed. It’s ideal to have 5 years’ worth of yield data for a given crop if possible. If you have 3 years, for example, and one of those years was a drought and another was a flood, then it will be difficult to find an accurate trend in yield across those 3 years. Another setback is that it does require you to have a yield monitor in your combine.
Conclusion
There you have it. These are some of the most commonly used methods and data sources to create yield zones with. In the end, you will have to decide on which method works best for you and your situation, but any of these methods provide more efficiency and precision than relying solely on soil test nutrient levels to determine your variable-rate program.
Please feel free to comment on this article at the bottom of the page if you have any thoughts you’d like to share on this topic. As mentioned in the previous article, Service and Supply is well-equipped to manipulate your data and create yield zones for you. When you purchase your fertilizer through our company, we create your yield zones and all variable-rate prescriptions FOR FREE. Use one of the contact links below to get in touch with your local Service and Supply precision agronomist today.
