October 13, 2020

Early plant vigour helps with boll set and reduce “low mic”

Crops that only develop small leaf areas will have a lower ability to capture light and generate energy for growth and fruit development. This can delay and reduce the numbers of fruiting sites produced and also lower retention rates.

With lower retention rates, crops generally have to be grown for longer to achieve targeted boll numbers. This can lead to a greater number of immature fruit at defoliation and “low mic” cotton.

To maximise potential vegetative growth rates, cotton plants need to convert resources into energy efficiently. A healthy leaf canopy is necessary to capture light and produce energy. Plant growth/development is driven by the following factors:

  • Temperature
  • Radiation
  • Available moisture
  • Nutrition
  • Root health



Generally, available moisture and nutrition are the only factors that can be managed during the growing season.  Root health will be influenced by previous crop rotations and management practices that have already occurred.

Maximising shoot growth will help to produce adequate carbohydrate/energy, which in turn supports root growth. Mitigating stress and optimising nutrient availability will support maximum plant growth.

Healthy root growth is the key to plants taking up nutrients from the soil, especially immobile nutrients. Generally, root growth occurs quickly under good growing conditions. However, root growth can be interrupted due to cold conditions or temporary nutrient shortage.

Trials conducted by Yara at the Pocklington Research Facility on cotton root growth responses to the foliar application of phosphorus (P) has shown that foliar application P can help boost cotton root volume by close to 50% (Figure 1) and increased root growth the greatest in 0-0.5 mm root diameter category (Figure 2).  This section of root system is very important for nutrient uptake, particularly immobile nutrients.

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Figure 1: Total root volume of untreated and treated plants 15 days after application of Foliar P.



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Figure 2: Root length by root diameter categories for untreated and treated plants 15 days after application of Foliar P.


The inclusion of Yara Liquids P-FOL Zinc @ 5 L/ha in your early season crop nutrition program will provide an effective strategy to support plant growth and canopy development before flowering.

Yara Liquids P-FOL Zinc is true liquids and can be easily tank mixed to suit application opportunities.

For more information on how to optimise your cotton nutrition program, please call your local Yara Sales Agronomist.