Alabama Cotton: Yield Response to Different Nitrogen Rates

    Green cotton bolls with a few mature. Photo: Seth Byrd

    Nitrogen (N) is the most required nutrient for most row crops. However, N rate and application timing represent a challenging decision. Different varieties, soil types, yield potential, nitrogen sources, soil moisture and weather conditions during the season play an important role in overall N management.

    A cotton N experiment was conducted at the Gulf Coast Research and Extension Center in Fairhope this season. Past studies in multiple crops have demonstrated limited responses to N at this location, suggesting that the standard approach to N fertilization in cotton in this environment may provide excessive N.

    The objective of the project was to identify the highest cotton yield response by applying different sidedress rates of N. The N source for the sidedress application was 24-0-0-3.

    The treatments were:

    1. Control (20 lbs N pre plant and no sidedress)
    2. 20 lbs of N pre-plant and 30 lbs of N sidedress, for a total of 50 lbs
    3. 20 lbs of N pre-plant and 60 lbs of N sidedress, for a total of 80 lbs
    4. 20 lbs of N pre-plant and 90 lbs of N sidedress, for a total of 110 lbs
    5. 20 lbs of N pre-plant and 120 lbs of N sidedress, for a total of 140 lbs

    The Table 1 below shows the management practices for the experimental field.

    Table 1. Field management practices

     Activity  Date
     Planting  20-May
     Seeding Rate  30,000 seeds/A
     N itrogen at Planting  20 lbs N
     Sidedress Application  9-Jul
     Harvest  3-Nov

    The 2021 growing season was a challenge due to the high precipitation (Figure 1) that occurred during the season. The field location received 44.4 inches from planting date to harvest, creating challenges in overall management.

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    Lint yields ranged from 750 lbs/ac to 900 lbs/A in the experiment. The treatment with 20 lbs of N before planting and the 120 lbs sidedress demonstrated the highest variability in yield between replications. The Figure 2 shows the response curve of cotton yield under the different N rates.

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    There were no significant differences among the treatments this year, presumably because of the high variability in the field. However, the treatment with a total of 80 units of N (20 lbs of N at planting and 60 lbs of N sidedress) achieved the maximum numerical yield, and a decrease in yield was observed with increased rates.

    As mentioned before, this year was a very wet year for the entire region and the experiment needs to be repeated the next growing seasons to understand the yield response in this environment.

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