Estimating seed counts in sorghum heads for making yield projections

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The process of estimating grain sorghum yield potential was discussed in last week’s Agronomy eUpdate (see:

The three key components needed to estimate grain sorghum yield are the number of heads per acre, the number of seeds per head, and seed weight (number of seeds per pound). Perhaps the most tedious of these components to measure is the number of seeds per head. The total number of seeds per head can vary from 100 to 5,000 seeds per head, but most heads have between 1,500 and 2,500 seeds per head. That’s a lot of seeds to count in just one head! A quick method of estimating seed counts would be useful.

Making a good estimate of seed number is especially important to getting a good estimation of yield. The number of seeds per head is better correlated with final sorghum yields than seed weight (Figure 1A &B, respectively).

Figure 1. Relationship between yield components, grain number per head (A, left panel) and seed weight (B, right panel), and final yield per plant.

As mentioned in last week’s article mentioned above, we are currently working on a new method for making a quick estimation of the grain number. In our new method, the estimation is based on predicting the final head volume.

We are exploring two approaches: 1) allometric estimations and 2) head imagery.

Allometric calculation: Briefly, the allometric calculation is an estimation of the head volume through measurements of head diameter (width) and length, with final calculation using a spherical volume equation (Figure 2). This tool provides a fair prediction of the final grain number (Figure 3).

In addition, we quantify the relative frequency in variation for head length and width for all sorghum heads. The most frequent numbers for head length ranged from 8 to 12 inches; while head width varied mostly from 1 to 3 inches. In average commercial sorghum hybrids, yield variation is more related to increments in head width than modifications in head length.

Figure 2. Allometric determination of head volume via measurement of head length and diameter (width). Photo by Ignacio A. Ciampitti, K-State Research and Extension.

Figure 3. Fair correlation between head volume estimation using the allometric method and actual grain number per head.

Head imagery: The second approach is via head imagery. In this method, all you need to do is take a photo of a head and the computer program will estimate the head volume. This approach seems to be more accurate and less labor-intensive than the allometric method. At present, we are working on a way to automatize this process and develop an App for making sorghum yield estimation prior to harvest.

There will be more details about this project in coming months.


Ignacio A. Ciampitti, Crop Production and Cropping Systems Specialist