In the past, to optimize the yield potential in their acres, growers planted varying seeding rates as they moved from field to field. They would increase or decrease blanket seeding rates for a whole field, enabling them to exploit as good as they could what each field had to offer in terms of yield potential. Lowering seeding rates in less productive fields helped them save dollars invested in soil that will not produce well enough to justify the investment in seed. However, as we all know, yield is not evenly distributed over the whole field.
Today’s technology allows growers to take the practice of applying varying seeding rates correlating with yield potential one step further. Modern planters coupled with the use of GPS technology have enabled growers to change the density of their seeding at the row level as they are planting. Growers aren’t manually adjusting their seeding rate as they drive through the field, the planter itself is automatically adjusting the seeding rates according to a map that the farmer has imported into his tractors computer. These maps are based on field data indicating where the high and low yield zones are. High-resolution NDVI imagery is an example of this type of data.
Variable Rate Seeding Prescription Map
The main goal of variable rate seeding (VRS) is to take full advantage of areas in a field with high yield potential while limiting resources spent on areas with low yield potential. The reduction of seed cost is a welcomed byproduct, but not the end goal. In order to determine where these high and low performing zones are, growers have historically relied on two pieces of data; soil data and yield data. Yield data, of course, will tell growers the end crop performance results for their fields. This information is an excellent indicator of where the high and low-performance zones in a field will be for the new season. However, conditions in a field change from season to season, as do zones of varying yield potential. The same can be said for soil data if it is not collected annually. While soil makeup does not change as regularly, fertility levels do as a result of the nutrient intake of the crop from the prior season, weather events and crop residue. To account for this, growers and their agronomist or precision ag specialist can create cluster maps or normalized yield maps. Cluster maps combine zones from different pieces of data such as yield and soil data into one map that represents both. Normalized yield maps combine multiple years of yield data into one map. The normalized yield maps tell the story of how a field has performed historically over multiple years, not just over the past year. This information can be valuable in determining how the field will perform during the season ahead. Growers are comfortable using yield and soil data to power their precision ag programs because that is what they know, but there is another type of data that offers information that neither soil nor yield data can offer.
High-Resolution Imagery Data for Variable-Rate Seeding
Using high-resolution aerial imagery data to power variable rate seeding programs is a relatively new idea. The imagery needed for guided VR seeding or applications, growers are predominantly using NDVI (Normalized Difference Vegetation Index) imagery, which is a crop health index that tells growers where their crops are thriving and where they are stressed. This NDVI data can be formed into management zone maps identical to those built from yield or soil data. Other types of imagery data, specifically thermal data, can also be very valuable for predicting yield zones. Thermal data is used to monitor moisture situations in fields which can impact soil nutrient levels, which in turn can alter yield potential. Growers and agronomist can run a VRS program powered by imagery in one of two ways; they can include NDVI zoning maps as part of a cluster map with other types of data, or they can make a VRS prescription from imagery alone.
NDVI imagery has proven that it strongly correlates to yield data, validating its ability to identify yield potential. So what value does imagery data offer VRS practitioners over yield or soil data? The answer is twofold. The first advantage aerial imagery provides is its detail. The value of any imagery data depends almost entirely on image resolution. For instance, for TerrAvion 10-17 cm imagery, each pixel is about the size of your hand. You can imagine the value that offers a grower to be able to view their entire field in 10-17 cm pixels. However, not all imagery is created equal. Satellite imagery is widely used for precision agronomy today because it is cheap or even free, but at 10 m per pixel, the value offered is minimal. High-resolution imagery, though, provides far greater detail than yield data. Yield data is collected by a harvester multiple rows at a time. A single pass of a combine can hold millions of NDVI pixels, each containing different bits of information. Yield monitors are also prone to calibration issues and other human errors. In precision agronomy, detail is critical, and the detail of high-resolution imagery is on an entirely different level than that offered by yield data.
The other advantage of high-resolution aerial imagery has over yield or soil data is timing. Yield data is provided one time at the end of a season, but conditions in a field can change drastically from the time of harvest until it's time to plant for the following season. The current weather situation in the Midwest is a prime example. The extreme flooding in the region is sure to alter nutrient levels across millions of acres. Early season thermal data helps growers determine precisely what parts of their fields have been affected by severe weather events. In the case of flooding, the flood areas are prone to nutrient leaching and can be targeted for heavier nutrient applications to bring the soil back up to the potential it had before the flooding. The image above is an example of a flooded field. This situation will dramatically affect the yield potential in parts of this field, and none of this information would have been included in a seeding prescription map based only on soil and yield data. Another example were TerrAvion's high-resolution imagery has an advantage, is when crop trash left behind after harvest. Crop trash can alter nutrient levels in a field, and early season NDVI imagery helps growers determine where that may be a factor.
Determining the optimal seeding rates for your field is not an easy task, but TerrAvion provides growers everything they need to run a VRS program. Our customers are supplied with the best value high-resolution imagery on the market, and our users have the ability to make thermal or NDVI management zone maps right in their TerrAvion OverView account. These maps can be exported as SHP files and imported to any farm management platform where you may be making a prescription or can be sent directly to an on-board controller.