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By Dusty Sonnenberg, CCA, Field Leader, a project of the Ohio Soybean Council and Soybean Checkoff
As we get closer to harvest, there is value in estimating the soybean crop’s yield. The closer we get to harvest, the more accurate the yield estimates become. Later-planted soybeans, replants, and double-crop beans will require more assumptions when gathering data. Marketing decisions and storage plans can be made and adjusted in a timely manner when a reliable yield estimate is available. There are several methods farmers can use to estimate crop yield. There are also A.I. tools now available to assist in the process.
Most methods require collecting basic information, such as plant populations, row spacing, pods per node, seeds per pod, seed size, node spacing, and average plant height in the field.
Shaun Casteel, Purdue University Extension Soybean Specialist, utilizes a soybean yield estimating method that takes the number of pods in 1/10,000 of an acre, multiplies it by the number of seeds per pod, and then divides by a seed size factor.
Based on the planted row spacing, measure 21 inches and then count the number of pods in 1 row for 30-in width, 2 rows for 15-in width, or 4 rows for 7.5-in width to equal 1/10,000th acre. Each of these counts will be 21 inches long.
The seed size factor ranges from 15 for large seed, to 18 for normal-sized seed, to 21 for small seed. The actual seed size can be difficult to determine until closer to harvest.
Mark Licht, PhD, associate agronomy professor at Iowa State University uses a formula that multiplies the number of plants per acre by the number of pods per plant by the number of seeds per pod. This number is then divided by the number of seeds per pound multiplied by 60 (pounds per bushel).
To determine the number of plants per acre, you need to count the number of pod-bearing plants in 1/1,000th of an acre. In 7.5-inch row spacing, count the number of plants in 69 feet, 8 inches of row. In 15-inch row spacing, count the number of plants in 34 feet, 10 inches of row. In 30-inch row spacing, count the number of plants in 17 feet, 5 inches of row.
Once the number of plants per acre is determined, the number of pods per plant must be calculated. Count the number of pods (containing one or more seeds) from 10 plants selected at random. Divide the total number of pods by 10 to get the average number of pods per plant.
To determine the average number of seeds per pod, count the number of seeds from 10 pods selected at random. In general, the number of seeds per pod is 2.5, but it may be lower in stressful environments. Divide the total number of seeds by 10 to get the average number of seeds per pod.
Assume that there are approximately 3,000 seeds per pound. If the soybean plants experience stress, seed size will be reduced. It will take more seeds to make one pound.
The University of Kentucky has created an online calculator for predicting soybean yields based upon sample data from your fields. They have provided a form that allows you to enter numbers, and calculate the estimated soybean yield.
On the Field Leader Crop Tour sponsored by the Ohio Soybean Council and Soybean Checkoff, a more generic observational method was used that factors in the number of beans per pod and number of pods per node, along with the distance between nodes and the average canopy height.
Famer Grows has an online calculator that can do the math for you with some basic information input. The Farmers Grow form factors include the number of plants per acre, the row spacing, the stand count in a pre-selected row length, the number of pods per plant, and the number of seeds per pod. This formula also factors in the seed weight, estimated grain moisture, and harvest loss percentage.
