Understanding Statistics

NASS Surveys: The Foundation of Estimates - Objective Yield Surveys

During the growing season, crop conditions and yields are monitored in thousands of fields by enumerators who count the number of plants and, later in the season, count and measure ears, pods, bolls, and so on. The crop development data gathered through these objective yield surveys are used to forecast yields and/or project production for corn, wheat, cotton, soybeans, potatoes, burley tobacco, onions, and a variety of fruits and nuts.

With the farmer's permission, enumerators walk a randomly selected number of paces into selected fields and mark off a small sample plot -- no matter what the condition of the crop at that location. This practice minimizes selection bias that could skew the final estimate.

At the designated field location, the enumerator counts the number of plants and measures the distance between rows to determine plant population per acre. Then the enumerator counts immature and mature fruit, such as cotton blooms and bolls: soybean branches, nodes, and pods: wheat heads and spikelets; or ears of corn, and records the crop's stage of development. With the data on plant population per acre and projected yield per plant, statisticians can forecast yield per acre at the State level.

All objective yield surveys except potatoes require enumerators to repeat their visits to the sample plots several times during the growing season. When the crop reaches maturity, they harvest a portion of each plot by hand and send samples to a laboratory for weight and moisture analysis. When the farmer harvests fields containing the plots, enumerators make their final visits to the sample plots to determine harvesting losses and estimate net yields.

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Last Modified: 01/26/2018