Technical Bulletin: Fertilizing Cotton with Polysulphate (polyhalite)

Polysulphate^® (polyhalite) as a Sulfur Source

Granular Polysulphate® is a natural mineral from underneath the North Sea that contains four nutrients: sulfur (19.2%), potassium (14% K2O), magnesium (3.6%), and calcium (12.2%). It is a single complex crystal that is mined, crushed, then ready to use on agricultural fields. This multi-nutrient mineral (polyhalite) is sold by ICL as Polysulphate and is OMRI certified, low in chloride and crop safe, suitable for use alone or in blends and compound fertilizers.

The risk of sulfur deficiency has increased in areas of the US where levels of atmospheric sulfur – from air pollution through fossil fuel combustion has declined. The US has seen sulfur dioxide emissions drop significantly. According to the 2021 US EPA progress report on acid deposition, emissions of sulfur dioxide have declined significantly in the eastern US since 2000 which has resulted in less sulfur reaching the soil. Sulfur fertilization is now an essential part of any fertility program in the eastern region. Polysulphate, a slow-release mineral fertilizer, has the capability to provide sufficient and continuous supply of S to satisfy the all needs of the growing crop.

Features of Polysulphate (polyhalite) Fertilizer

1. Slow-release mineral fertilizer that has the capability to provide a sufficient and continuous supply of S to satisfy all the needs of the growing cotton crop
2. Natural multi-nutrient mineral with every granule composed of sulfur-based potassium, magnesium and calcium that is low chloride, very low salinity index, neutral pH, no acidifying effect and safe to apply
3. Excellent spread and blendability when applied via broadcast, precision application when used in a band, and superb blendability with other common fertilizers
4. Flexible application that can be applied as a pre-plant or at planting with proven results across a variety of crops and soil types
5. Natural mined mineral (polyhalite) approved for organic agriculture that helps to improve nutrient efficiency, soil structure, root development, water infiltration, and seed emergence

Source: University of Nottingham, UK, 2016

Function of S, K, Mg, and Ca in Cotton

• Sulfur (S) is an essential constituent of proteins: it is required for the synthesis of three of the amino acids which make up true proteins.
• Potassium (K) secures yield and quality, transport of sugars, stomatal control and is a co-factor of many enzymes. It reduces susceptibility to plant diseases and impact of drought and is essential for efficient use of nitrogen.
• Magnesium (Mg) is fundamental for photosynthesis, being a central part of chlorophyll molecule, and is important for carbohydrate transport to sink organs.
• Calcium (Ca) for strong and healthy crops; it is a major building block in cell walls and reduces susceptibility to diseases.

Nutrient Removal by Cotton 2 bales/A

Practical guidelines for fertilizing cotton
with Polysulphate

• Single Polysulphate application at pre-plant or planting will supply all the cotton crop’s S needs.
• Polysulphate can be applied alone or in a blend as part of a fertilizer program to meet the cotton K and Mg needs.
• Polysulphate applied at 200 lbs/A can supply 100% of the S, Ca, and Mg, and 90-100% of the K depending on soil test level.
• Polysulphate can be applied early spring before field preparation to reduce competition for application and storage equipment usage.
• Season-long continuous supply of S is needed to balance nitrogen and increase nitrogen use efficiency.
• Consulting with agronomists or soil experts can help in determining the rate and application timing to meet your specific need.

Featured Trials

POLYSULPHATE INCREASED YIELD BY 20% OVER THE CONTROL

• Four replications of each treatment
• Control 0-0-60 applied at 120 lbs K2O per acre
• Polysulphate applied at ~28 lbs of K2O per acre (200 lbs/A)
• Potassium magnesium sulfate applied at 28 lbs of K2O per acre (133 lbs/A)
• Polysulphate was used at lower rate than KCl because the calcium (Ca) and magnesium (Mg), traded places with potassium in the soil. This swapping made more potassium available for the plants.

POLYSULPHATE INCREASED YIELD BY 12% OVER THE CONTROL

• Control: North Carolina (NC) – 20 lbs of S and no K2O or Mg; Georgia (GA) – no Mg or S and 120 lbs of K2O; Texas (TX) – no Mg, S or K
• Polysulphate applied at 200 lbs/A
• Studies were done in 2023, in replicated plot trials with four reps per treatment

POLYSULPHATE + FLOW INCREASED YIELD BY 20% OVER THE CONTROL

• Polysulphate applied 200 lbs/A and foliar-applied Nova FLOW (5-10-20 11S, 9Mg, 0.5B) applied at early bloom at 5 lbs/A in Georgia (GA) and 10 lbs/A in Texas (TX); Average across two trials done in TX and GA
• Control: GA no Mg or S and 120 lbs of K2O; TX no Mg, S or K
• Studies were done in 2023, in replicated plot trials with four reps per treatment

*Significantly different from the control at P <= 0.10

† 208 lbs/A of Polysulphate was applied in the Georgia trial in 2020 and 2021, and 200 lbs/A in 2023