Zoning In On Precision Ag

New technologies help growers pinpoint management zones to improve the bottom line.

Precision farming is an art and science of utilizing advanced technologies to enhance grain yields in an economic and environmentally sensible manner.

Our goal is to maximize ag-input use efficiency, or in other words maximize net dollar return per acre from the fields, increase grain yields, protect environment, and enhance farm profitability.

We have been practicing crop production for centuries. And during this time period we all have realized that when we harvest our crops year after year, the grain yields harvested from different areas of a field are not uniform (Figure 1). For example, you have a 160-acre cornfield or a quarter section center pivot cornfield, there are areas within the same field that produces different levels of grain yield. The grain yield variability in one field can range from to 300 bushels/acre. Well we all have observed that for a long time. The question is, what can we do about it?

Is there something we can do to enhance our production and bottom line?

In the past, we did not have the technology to quantify these differences in grain yield. Thanks to precision farming technology we can now locate, measure and record such areas in the field that produce below or above the average grain yield of the whole field (Figures 2 & 3). Not only that but precision farming provides us the tools and the opportunity to manage the grain yield variability that exist in our fields.

The big question is: “How do we manage this grain yield variability that exists in our farm fields to maximize our net $$ return?” Managing grain yield variability The first approach that we all started practicing and evaluating as researchers and consultants was Grid Soil Sampling (Figure 4). However, very soon we realized that grid soil sampling is time-, labor- and cost-intensive. Besides, it needs to be performed on each field and almost every year or so and therefore becomes cost prohibitive. There has been a need for a method of managing variability in our farm fields that is stable, less cost- and labor-intensive that can be used for several years and can still manage grain yield variability in a profitable manner.

Figure 2. Yield Monitor used to locate, measure, and record yield.

In the last few years, ongoing research conducted by scientists from CSU, USDA-ARS, Colorado has created a system to divide farm fields into different sections or areas that are referred to as productivity level management zones. This was accomplished based on: Farmer’s personal experience and grain yield history, Aerial imagery of bare soil and other stable soil properties, such as organic matter content, and Topography of the land.

Using this method we can divide our fields into at least three different management zones based on the productivity potential of each area. They are: Management Zone 1--high yielding Management Zone 2--medium yielding Management Zone 3--low yielding Our ongoing research has shown that these management zones are real and there are significant differences in the grain yield across management zones.

Concept of Management Zones I think the concept of management zone is easy to understand. If we look at the fingers of our hand, they all belong to the same hand, but their sizes are different. The three management zones can exist in the same field, but their production potentials are different (see Figure 5.) No matter how much water and nutrients we may add, the grain yield in each region is limited to the productivity potential of that zone. You can estimate the maximum yield potential of each zone through years of farming experience and yield monitoring. Going back to the “fingers of our hand example” above, no matter how much we may stretch our fingers they are not going to increase in size. I am not suggesting that there is no further potential for our crop yields to increase, I am suggesting that the three management zones “Low, Medium, and High” are based on the productivity potential of the soil. The question then becomes: Should we be applying the same amount of nutrients across the field? For example, if Zone 1 has the potential to produce 200 bushels, Zone 2 has the potential to produce 175 bushels and Zone 3 has the potential to produce 150 bushels or more. It is quite logical that we do not need to apply the same amount of nutrients across the field when we know that the nutrient needs are different for different areas of the field. If your inputs are based on the highest yield goal, you know you are over applying in Zone 2 & 3. If you target your input application based on the average yield goal, you know you are under-applying for Zone 1 and over-applying in Zone 3.

Managing nutrients within zones

It is a general feeling among folks I have talked to that if they apply more inputs (water and nutrients) to low yield management zones they will be able to bring the grain yield level up to the level of the most productive management zone.

This is similar to saying there are three people, “Big & Strong”, “Medium-built” and “Short & Puny” and that if we feed a lot (a huge meal) to the “Short and Puny” person, we will be able to get the same amount of work done out of the “Short and Puny” person as compared to the “Big & Strong”. We all know that’s not going to happen. There may be some exceptions, but generally speaking, if we feed the “Short & Puny” guy the same huge meal as the “Big & Strong” person, the “short guy” most likely will be running back and forth to the bathroom.

The point I am trying to make is that different areas of the field have different productivity levels, and merely applying more inputs to low productivity areas are not going to translate into more grain yields. Instead we may lose or leach that extra water and nutrients out of the soil below the root zone and increase the potential for leaching of nutrients to ground water slowly over time. Instead of applying the same amount over the field, the nutrients should be tailored to fit the potential of the management zone, just as you would tailor a coat to fit the size of the person’s body.

The key to managing variability that exists in our farm fields is to optimize the application of our agricultural inputs to different regions or “management zones” of the field based on their inherent productivity potential.

For more information, please feel free to contact me at 970-491-1920, or by e-mail at Raj.Khosla@colostate.edu.

by Raj Khosla
Extension Specialist for Precision Agriculture
Dept. Soil and Crop Sciences
Colorado State University