Grain yield monitor

Grain moisture content at harvesting is an important piece of the yield monitoring process. It is used in many cases, dependent upon manufacturer, in the grain mass flow sensor calibration and provides producers with additional information about spatial variability within a field. Grain moisture is sensed by measuring the capacitance of the grain by passing a known grain volume between two electrically conductive plates. Typically this sensor is mounted on the clean grain elevator and a sample metered into the sensor and back into the clean grain elevator after it has been processed.[7] This sensor orientation allows for sampling grain moisture throughout a field during harvest operations.

Measurement of grain yield comes from the measured grain mass flow, the harvester speed, and header width. Grain moisture as determined by the moisture sensor or by operator input into the yield monitor can also be included to estimate dry grain mass. In the United States the grain yield is typically reported as bushels per acre. SI units for grain yield measurement are typically reported as tonnes per hectare or in few cases m³. The harvester speed can be obtained by ground speed measurement from measuring the wheel speed of the harvester, radar mounted on the harvester, or by GPS. The head, as it is referred to is the device mounted on the front of the harvester by which the crop is gathered into the harvester. The width of the head is determined by the effective width of crop that can be harvested as the combine moves in the forward direction.

Variable	SI Units	Imperial	Description
${\displaystyle {\dot {m}}}$	kg/s	lbs/s	Grain Mass Flow
${\displaystyle v}$	${\displaystyle {\tfrac {kilometer}{hr}}}$	${\displaystyle {\tfrac {mile}{hr}}}$	Harvester Velocity
${\displaystyle w}$	m	ft	Head width
Yield	${\displaystyle {\tfrac {tonne}{ha}}}$	${\displaystyle {\tfrac {bu}{acre}}}$	Grain yield as most commonly reported

Grain Yield as calculated for corn at 56 lb/bu in imperial units.

${\displaystyle Yield={\dfrac {{\dot {m}}*{\dfrac {bu}{56lb}}*{\dfrac {3600s}{hr}}}{w*v*{\dfrac {5280ft}{mi}}*{\dfrac {acre}{43560ft^{2}}}}}}$

Grain Yield as calculated in SI units.

${\displaystyle Yield={\dfrac {{\dot {m}}*{\dfrac {tonne}{1,000kg}}*{\dfrac {3600s}{hr}}}{w*v*{\dfrac {1000m}{km}}*{\dfrac {ha}{10,000m^{2}}}}}}$

The yield monitor is the device that records the data that determines the grain yield and the grain yield itself. Today's yield monitors provide operators with a user interface that displays the grain yield, grain moisture, and a color coded spatial map that displays the grain yield of the harvested portions of the field. The operator can enter additional information to separate and identify yield data from different fields and farms. Yield data can be downloaded from a yield monitor via the memory storage method used per the manufacturer and loaded into a spatial data management system. These software packages allow for viewing of the yield maps and completing other analysis of the data.

Yield map

Soybean field yield map

Grain yield maps can be displayed on a yield monitor or via a spatial data management software such as SMS or Apex. Yield maps are used in management decisions such as fertilizer application rates and seeding population rates in support of site specific farming.[8] Yield maps are also utilized for making decisions on best management practices in terms of comparing crop varieties, fertilizer types and application rates, and pesticide application. These other precision agriculture practices can be recorded as spatial maps and overlaid with grain yield maps for further analysis and decision making.

Grain yield monitors have been in production since yield monitors were introduced in the early 1990s and have been progressively updated with better hardware that provides the harvester operator with a better user interface and makes the logged data information more readily available. These monitors are typically referred to as displays in reference to their purpose in many cases is to display the yield information in a spatial color coded map.

Distribution of grain yield monitor accuracy for multiple loads

The grain yield monitor is an excellent tool that provides producers an effective evaluation tool on a field and farm basis. The accuracy of the yield monitor is approximately 1-3% when properly calibrated, but is on an averaging basis for this accuracy.[9] On a pass to pass basis the accuracy decreases significantly with a range of accuracy of 0-10% error in most studies.[10][11][12] The average of multiple loads remains within the projected 1-3%, but individual loads have a much higher variability. These errors are present from issues listed in the "Impact Based Mass Flow Measurement" section of this page. The effects of individual load variability limits its ability to be used for smaller scale comparison such as test plot comparisons. Test plots are usually single planted strips of a single crop hybrid at approximately the width of the combine harvester head. Harvesting a test plot results in single harvested load and yield estimation for the single hybrid. Comparing one hybrid to another based on single loads can be difficult as the load is essentially a sub sample of a larger mean.[13]

US patent 6899616, David L. Murray, "Mass Flow Grain Monitor and Method", published 2005-05-31, assigned to ACOO Coroporation, Duluth, GA(US)

US patent 5686671, F.W. Nelson; W.F. Smith & K.R. Hawk et al., "Grain Mass Flow Sensor For An Agricultural Combine", published 1997-11-11, assigned to Deere & Company, Moline, IL(US)