Early planted(before mid-May)soybeans likely have sizable beans in the pod so you can begin estimating yields now for marketing and other purposes. First determine the length of a “one row acre”. For example, beans in 30 inch rows have 17,424 feet in a row acre, in 15” rows that length is 34,848 and with 7.5” rows its 69,696. Walk around several (10 or more)places in a field and count the number of plants per foot of row(6 might be normal for 30”rows, 2.5 for 7.5” rows). Determine the average and multiply by your “one row acre” feet. At each spot you stop, break off a plant at the soil surface and carry it with you. When you get back to your farmstead, find a table under a shade tree, pour your favorite beverage and start counting the number of pods per plant and determine the average number that have at least one seed in the pod. Now strip off 2 pods near the top, 2 pods in the middle and 2 near the bottom of each plant and count the seeds per pod and get an average. Now you can multiply the average number of plants per acre times the average number of pods per plant times the average number of seeds per pod. Do not round off numbers on any of these! Now you have arrived at the number of seeds per acre and you need an estimate of the weight of the seed(seeds per pound). If you saved seed tags from planting seed, this is a good place to start. This year’s planting seed was in general smaller than normal and if we continue to have adequate rains, seed size should be larger. So if your tag says 3000 seeds per pound, use 2800. If you have no tags use 2800 as an estimate. Divide 2800 into the number of seeds per acre that you calculated above. This will give you pounds per acre which you can divide by 60 to get bushels per acre. As an example, a field of 30 inch row soybeans has 6.5 plants per foot of row, 32 pods per plant and 2.4 seeds per pod and a seed size of 2700 would have an estimated yield of about 54 bushel per acre (17424 x 6.5 x 32x 2.4 = 8,698,061 seeds/A divided by 2700 = 3221 lbs/A divided by 60 = 54 bushel/A). Remember all this is predicated on you making good and repeated estimates and no severe storms or other problems before harvest.
Zane R. Helsel