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Use Your Elevation Data For Drainage

Very often there are big similarities between yield maps and elevation maps, so elevation helps explain a lot of the variability within the field, and helps the agronomist produce crop plans to reduce this variability.

GPS units can collect elevation data throughout the field, which can be used to build a topographical maps. The question: Can I use elevation readings from my combine or sprayer for drainage applications in my field?

ANSWER

The answer comes from Simon Knutson, Agri-Trend Geo-Coach:

If you have RTK, we could definitely use your elevation readings to generate topography maps and drainage prescriptions. If you don’t have RTK, the maps will probably not be accurate enough to make effective drainage plans.

Ideally, you also need swaths less than 50 feet. The narrower the swath width, the more accurate the maps will be. That simply means you’re making more passes up and down the field and those passes are closer together.

For that reason, data from your combine yield monitor are going to be a more effective source than sprayer data in most cases and would also provide you with a direct comparison of the effects of topography and drainage on yield.

Usually it is also necessary for us to survey the in-field ditches or sloughs as well as any surrounding ditches and culverts using an ATV to ensure an accurate drainage map can be produced. This is important because there may be parts of the field that large equipment can’t drive through. These are often the areas you are looking to improve drainage in, so it is vital that they are mapped, too. In addition, knowing the elevations of culverts and ditch bottoms allows us to ensure that drainage plans will be effective and will highlight potential issues.

FOLLOW UP QUESTION

Are ditch digging companies set up to use a GIS map to determine where drainage ditches need to go and now deep they should be?

Answer: I’d estimate that virtually all tile drainage contractors are using either RTK GPS or laser systems for gradient control, and the majority of companies offering surface drainage have at least a laser system.

If the operator is using RTK then it should be simple to calibrate that system to the maps we produce so that they can run off our maps. If lasers are used, our prescriptions include the required slope gradients, so the operator simply enters the required gradient and either follows ground markers that we can lay or uses a laptop computer with a GPS connected to guide them along the cut lines.

FOLLOW UP QUESTION 2

What other uses, besides drainage, are there for accurate elevation numbers?

Answer: In many cases we’ve found elevation to be extremely important in other aspects of precision farming. For example, very low areas of the field may always be prone to drowning and therefore require fewer inputs, and likewise features such as eroded knolls may require different fertility rates than other parts of the field, so accurate elevation maps can help define production zones in these cases.

Very often there are big similarities between yield maps and elevation maps, so elevation helps explain a lot of the variability within the field, and helps the agronomist produce crop plans to reduce this variability.

Having accurate elevation data can also help us better understand relationships between other data layers such as yield and Veris (soil EC) maps. Veris maps highlight variability in soil texture, which matches well with yield in many cases, but sometimes we may see areas of surprisingly high or low yield given the soil texture. Often an elevation map will help explain what is happening, and it may be a zone of very sandy soil in a low-lying area that doesn’t drown out like heavier soils around it, or a heavier soil on a hilltop that is holding more moisture and therefore producing higher yields than similar soils in other parts of the field.

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