Increasingly yield maps are being used to make field level management decisions such as plant population, type of hybrid, fertilizer application, and soil drainage. Sometimes yield maps are used for crop insurance information or provided to landowners as part of the equation in generating a land rental agreement or payment. Yield maps are used to garner bragging rights at the local coffee shop. So consider these points; yield maps are generated from the information collected during harvest by yield monitors and secondly, accurate yield monitor information is dependent upon calibration.
This year our weather conditions have created a lot of field variability that will translate into expected yield differences within and between fields. Calibration of the yield monitor so that it can account for these variable conditions is necessary to collect reliable harvest yield data. Some good recommendations and procedures regarding yield monitor calibration can be found in two recently written articles; one written by Bob Nielson at Purdue University and available at: http://tiny.cc/PurdueYldMonCalibr and the second written by John Fulton, Andrew Klopfenstein, Kaylee Port and Scott Shearer at The Ohio State University, click on the following link to read the entire article: Yield Monitor Tips for 2015 Harvest. Below, I will highlight some of the information in those articles.
Yield monitors do not measure actual yield. Yield monitors estimate yield based on the electrical signals they receive from a mass flow, mass impact or optical sensor. Generally these sensors are located in the clean grain elevator and provide an estimate of grain flow per set travel time. In order to estimate the grain yield the yield monitor uses the flow rate, an estimate of distance traveled dependent upon GPS positions, the combine header width and an estimate of grain moisture content. Calibration involves harvesting loads of grain that will represent or mimic the range of grain flow (yield levels) that will be encountered when harvesting a field. Essentially calibration is teaching the yield monitor how to interpret the electrical signals it is receiving from sensors and then convert those signals into grain flow rates. Typically, varied grain flow rates are simulated by either running the combine at different ground speeds or harvesting strips of varying widths.
Some general rules of thumb regarding yield monitor calibration are:
1) Corn and soybeans require separate mass flow calibration.
2) A different calibration is required for high moisture corn (≥20%) versus lower moisture corn.
3) A different calibration is needed for “green” versus dry stem soybeans.
4) Grain test weight can influence mass flow sensors so again, you might need to manage different calibration numbers as test weight differs by 2 or more values between fields.
5) Double check calibration routinely for a crop and operating conditions.
6) Remember to calibrate grain moisture sensor for each crop.
7) Calibrate temperature sensor for those monitors requiring this step.
Yield monitors are capable of providing valuable information that can be used to make future management decisions as well as mapping current crop yields. The key to ensuring that this information is accurate and reliable is calibration. Yield monitors come with a user guide that provides details about the calibration procedure. Take the time before harvest to read through the user guide, familiarize yourself with calibration procedures and then calibrate the yield monitor. It is time well spent.