“Harvesting” Yield Monitor Plot Data with Free GIS Software


What’s my optimum corn population? Does the yield response for primary tillage cover its costs compared to reduced tillage? Does the additive this salesperson is promoting provide a yield response on my farm? They say you don’t know what you don’t measure. Many options exist for extracting yield monitor harvest data from on-farm trials. Some require paying for software or apps, software or app upgrades or subscriptions. There are also many for-hire services that offer this. If you already have access to software or services that do this, or plan to do lots of comparisons, these are likely better or quicker options.

If you have data you would like to analyze yourself, don’t currently have software that does so, and aren’t afraid of new software, this article demonstrates a free option to analyze yield monitor data from plots. If a picture is worth 1,000 words, a video is worth at least 1,000,000. I’ve made step-by-step videos outlining the process, about 40 minutes total.

Step 1: Dowload QGIS

QGIS is likely the standard for free, open-access GIS (geographic information system) programs. QGIS can read in spatial data (e.g. yield monitor layer), allow you to create new spatial layers (e.g. plots) and do analysis of data layers (e.g. average yields within plots) among countless other things. It’s freely available at www.qgis.org/en/site/.

Pros include it is free and there is great open documentation, forums and videos to find solutions to your questions. These eight steps were entirely learned from no prior QGIS experience, and an afternoon of browsing forum posts and YouTube videos from internet searches. Cons include it cannot read monitor data directly (must be converted to GIS-standard SHP file format first), is not as quick as other software or apps (some can do these analysis with a couple swipes of a finger on a phone or tablet) and may not do everything high end GIS software can.

I’ve found this helpful for summarizing yield data when I don’t have access to software I would normally use (e.g. COVID lockdown) or working with colleagues who would like to summarize data from their trials but don’t have software to do so.

The steps will be further described in a series of videos that are linked within this article. Each video is approximately 5 minutes long.

Step 2: Read in Yield Monitor SHP File

The first step in summarizing yield monitor data is to read your yield monitor SHP file into QGIS. This requires pulling data from your combine monitor, uploading it to your monitor’s software program (or another that can read your monitor’s file format) and exporting data from individual fields as SHP files for analysis into QGIS.

Step 3: Source QGIS Roads and/or Imagery Layers

Your QGIS download may only come with open access street maps background. While not critical, I prefer using a background layer providing imagery or street names. This video demonstrates how to load an imagery background, in this case Google map’s satellite imagery layer, as a background.

Step 4: Visualize Points Data

I like to visualize data so I know what I am looking at, observe general trends across the field and to provide some quality control or outlier detection when looking at the data layer. This video outlines how to colour-code points in your yield monitor data layer by yield value in QGIS.

Step 5: Add QGIS Numerical Digitize Plugin

You will need some guidance as to which combine passes belong to which test plots. If you have GPS co-ordinates for pre-marked stakes or edges of plots (e.g. from cell phone), enabling this plugin allows you to manually enter new points and enter custom GPS coordinates in QGIS.

Step 6: Add Plot Stakes or Boundaries

Displaying plot markers is useful for lining up proper combine passes with plots, and properly creating and labelling plot boundaries. This video describes how to create points for plot stakes or boundaries in QGIS, adjust their appearance, and display labels for each one.

Step 7: Add and Name Plot Polygons

Once we know which combine passes line up with which plots, we need to outline the plot area over the yield monitor data for each plot. This video outlines how to create and copy polygons for each plot and name each polygon to reflect the plot or treatment underneath it for easy data summarization in QGIS.

Step 8: Average Yield Monitor Values Within Plot Polygons

This video shows how to summarize plot data in QGIS by joining yield monitor data points within each plot to the polygon delineating the plot. Once joined, we can save this as a new layer and create a summary table with yield monitor values summarized by each plot.

In Conclusion

While this example was specific to a plot stake, combine yield monitor data summary, QGIS is generic enough that it works for creating layers or analyzing or summarizing data from many different spatial applications or sources. This was merely one example to show possibility of what can be done.