Corn Objective Yield Procedures

Reference Sheet

Number of Ears per Acre Average Ear Weight

Field Field/Lab

Counts Measurements

Stalks Model 1: Stalks 5-Year Average Historical

Model 2: Stalks with Ears Average Weight per Ear

Number of Ears per Acre Average Ear Weight

Field Field/Lab

Counts Measurements

Stalks Model 1: Stalks 5-Year Average Historical

Stalks with Ears Model 2: Stalks with Ears Average Weight per Ear

Ears and Silked Ear Shoots or Ear Shoots

Ears with Evidence of Kernel Formation

Number of Ears per Acre Average Ear Weight

Field Field/Lab

Counts Measurements

Stalks Model 1: Stalks Length of Kernel Row Model 1: Kernel Row Length

Stalks with Ears Model 2: Stalks with Ears Diameter of Ear Model 2: Ear Volume

Ears and Silked Ear Shoots or Ear Shoots

Ears with Evidence of Kernel Formation

Number of Ears per Acre Average Ear Weight

Field Field/Lab

Counts Measurements

Stalks Model 1: Stalks Length of Kernel Row Model 1: Kernel Row Length

Stalks with Ears Model 2: Stalks with Ears Diameter of Ear Model 2: Ear Volume

Ears and Silked Ear Shoots or Ear Shoots

Ears with Evidence of Kernel Formation

Most "spikelets" liquid. Most silks protruding from husks are beginning to turn color.

Shoot has some silks showing. Little or no watery, clear liquid present in "spikelets."

Maturity Code 2 - Pre-blister

Maturity Code 1 - No Ear Shoots

No ears or ear shoots are present. 

Maturity Code 3 - Blister

Model(s) Model(s)

Model(s)

Model(s)

Model(s)

Model(s)

Model(s)

Model(s)

Maturity Code 4 - Milk

Plant or shuck is green. Ears are erect. Little or no denting. Most kernels are full of milk-like substance, but kernels not fully grown. 

Silks protruding from husks have turned brown and dry.
Number of Ears per Acre Average Ear Weight

Field Field/Lab

Counts Measurements

Stalks Actual Ears with Evidence Length of Kernel Row Model 1: Kernel Row Length

Stalks with Ears of Kernel Formation Diameter of Ear Model 2: Ear Volume

Ears and Silked Ear Shoots Weight of Ears

Ears with Evidence of Kernel Formation

Number of Ears per Acre Average Ear Weight

Field Field/Lab

Counts Measurements

Stalks Actual Ears with Evidence Length of Kernel Row Model 1: Kernel Row Length

Stalks with Ears of Kernel Formation Diameter of Ear Model 2: Ear Volume

Ears and Silked Ear Shoots Weight of Ears Model 3: Maturity 6 Ear Weights

Ears with Evidence of Kernel Formation

Number of Ears per Acre Average Ear Weight

Field Field/Lab

Counts Measurements

Stalks Actual Ears with Evidence Length of Kernel Row Actual Weight of Ears

Stalks with Ears of Kernel Formation Diameter of Ear

Ears and Silked Ear Shoots Weight of Ears

Ears with Evidence of Kernel Formation

https://www.nass.usda.gov/Education_and_Outreach/Understanding_Statistics/Yield_Forecasting_Program.pdf

This document is intended only as a quick reference guide. For full details, please reference "The Yield Forecasting Program at NASS" at

Weight Model 3: Harvested ears are laboratory weighed and adjusted to 15.5 percent moisture. These MC6 weights are related to final grain weights by means 

of regression.

Model(s)

Model(s)

Model(s)

Maturity Code 7 - Mature

Corn is about ready or ready for harvest. The maturity line on the kernels extends inward to the cob. No milk can be squeezed 

from the top of the kernels next to the cob when punctured with a thumbnail. Kernels shell off the cob fairly easily. When you pick 

a kernel from the cob, there may be a dark spot on the cob where the kernel was attached. Shucks are dry and are beginning to 

open up. No green foliage is present.

Ear Model 1: Uses five years of historic data to estimate the relationship between final ears per sample and the historic stalk count from the same month.

Ear Model 2: Uses five years of historic data to estimate the relationship between final ears per sample and the ratio of stalks with ears to total stalk

counts per sample.

Weight Model 1: Kernel row measurements, collected over a series of years, are utilized to forecast future sample grain weights.

Weight Model 2: Ear volume measures are calculated by combining kernel row length measures with cob diameter measurements. These are historically 

related to final grain

Model(s)

Model(s)

Model(s)

Maturity Code 5 - Dough

About one-half of kernels showing dent with some milk or dough-like substance in all kernels. Kernels full grown. Maturity line has 

not moved halfway to the cob on majority of kernels. Shucks taking on a light rust-colored appearance. Ears beginning to lean 

away from stalks.

Maturity Code 6 - Dent

Ears are firm and solid. Kernels fully dented with no milk present in most kernels. Shucks are about dry but not beginning to open 

up. Kernels may be hard to scratch at surface, but still soft near the cob. Maturity line on the kernels has not reached the cob.