Potassium Uptake and Cotton Yield and Quality
Nutrient Uptake and Removal
Cotton has a high daily requirement for potassium. Maximum uptake rates of 3.7 kg/ha/day and a total crop uptake of over 200 kg/ha have been measured in New South Wales.
Removal of potassium from cotton fields can also be high and will depend in part on crop residue management. In a crop yielding 7 bales/ha, up to 90 kg potassium/ha is stored in boll walls, 40 kg potassium/ha in seed and 15kg potassium/ha in lint. Where crop residue is windrowed or burnt, distribution of potassium across the field will be affected.
Low Soil Potassium Can Reduce Cotton Yield and Quality
In some Australian cotton growing areas, soil potassium reserves have been depleted to the point where cotton yield and lint quality are adversely affected.
In the Emerald Irrigation Area of Queensland, many paddocks are responsive to applied potassium fertilisers. Trials have confirmed that economic responses to potassium fertilisers are common where soil exchangeable potassium content is below 0.40 cmol(+)/kg. At one site with a soil exchangeable potassium content of 0.12 cmol(+)/kg, lint yield was improved by 24% by banding 125 kg potassium/ha in the bed prior to planting, and 8% by applying the same rate of potassium in the flood irrigation water two weeks after first flowering. (See graph.)
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This graph shows cotton yield response to potassium fertiliser application on a low potassium soil in the Emerald Irrigation Area. |
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Other regions with areas which are responsive to potash fertiliser include the Darling Downs and Macquarie Valley.
North American research has shown that cotton fibre quality can be adversely affected by poor potassium nutrition. In California, fibre strength has been shown to be positively related to soil potassium and mid-season leaf potassium content. Fibre length, micronaire, uniformity ratio and elongation have also shown positive correlations with potassium fertility in a variety of studies.