The Importance of Good Potassium Nutrition of Sugarcane
Robert Mullen, Ph.D.
Director of Agronomy
To say Dr. Robert Mullen is passionate about agriculture would be an understatement. He holds a Bachelor of Science degree in ag business from Cameron University, along with a Master of Science degree in plant and soil science and a Ph.D. in soil science from Oklahoma State University. In addition, Dr. Mullen has been published in a variety of scientific and trade journals. But it’s not just his academic accomplishments that make him unique. It’s his unwavering ability to take complex data and — in simple terms — explain how it impacts a farmer’s bottom line. Dr. Mullen delivers the kind of insightful observations that can lead to a more profitable business. As a leading agronomy expert, Dr. Mullen has a goal to further educate farmers on best management practices that improve their yields and maximize their return on investment.
In 2016, the United States produced over 30 million tons of sugarcane on just under 900 thousand acres (primarily in Florida and Louisiana). Sugarcane is a large biomass producing crop that takes up and removes a considerable amount of potassium from the soil. A 50-ton-per-acre sugarcane crop takes up around 350 pounds of K2O per acre, and approximately 175 pounds of K2O per acre is removed with the harvested stalk. So just what are the implications of poor potassium nutrition on sugarcane biomass production and ultimately sugar yield?
Role of Potassium in Plants
Potassium plays many roles in plants. We often focus on its role in maintaining osmotic potential and impacting water relations with the soil, but it also plays an important role in enzyme activation of reactions that impact photosynthesis and protein synthesis as well as facilitates translocation of proteins and sugars from sources to sinks (leaf tissue to harvestable material).
Remember, in most crops (specifically grasses), as a plant produces biomass it takes up a considerable amount of potassium in the process, and as reproductive growth starts, potassium uptake from the soil decreases (in most cases 90% of the total potassium that will be taken up is completed prior to reproductive growth).
The actual amount of potassium moved from the leaf tissue to the harvestable material (usually seed) is quite low compared to the actual amount taken up from the soil (25-30%). In the case of sugarcane, however, more than 50% of what is taken up in the plant is removed in the harvested stalk (Coale et al, 1993). This results in more rapid depletion of soil potassium than most other grass crops that are not completely harvested (grain/seed crops).
Managing Potassium in Sugarcane Production
The need for supplemental potassium fertilizer is primarily dependent upon potassium availability within the soil (typically measured by soil test). The more deficient the soil, the greater the need for potassium fertilizer. While clay/loam soils that dominate the Midwest can have large amounts of total potassium per acre, soils typical of the Southeast/South where sugarcane is cultivated are generally coarser textured, meaning substantially lower total potassium. This is especially true of muck soils in the Florida Everglades where sugarcane is cultivated (McCray et al., 2006).
The timing of potassium fertilization does not appear to be as critical as rate (unless you are growing sugarcane on very sandy soils that are capable of leaching potassium – then smaller, more frequent applications would be recommended). Application can occur prior to new planting, but applications can also occur in ratoon crops if deficiencies exist. Application rates for new planting are generally higher than applications in ratoon crops.
Potassium Impacts on Biomass and Sugar Yield
Beyond increased biomass accumulation associated with proper potassium fertilization (i.e., higher yield), there are also implications for sugar accumulation in the stalk. As an example of the importance of potassium nutrition on sugar translocation from the leaves to the storage tissue in the stalk, Hartt (1969) reported the rate of translocation of well potassium-fertilized sugarcane over the course of 3 months was 1.4 centimeters per minute, but the rate of potassium-deficient sugarcane was half that (0.7 centimeters per minute). Potassium-deficient sugarcane can cause more sugar to be retained in the leaves (due to slower translocation rates), ultimately decreasing sugar content of the cane at harvest.
Additional evidence exists to show the linkage between increased biomass production due to increased potassium availability and increased sugar translocation to the stalk. Donaldson et al. (1990) conducted four experiments (three that showed response to potassium fertilization) to evaluate potassium fertilization on sugarcane biomass yield and sugar yield (Figure 1). At all three locations, potassium fertilization resulted in increased biomass production (27% higher at experiment 1; 31% higher at experiment 2; and 20% at experiment 3) and higher sugar yield (30% higher at experiment 1; 38% higher at experiment 2; and 24% at experiment 3). Of note is the fact that the higher biomass yield does not account for all the increased sugar yield. The potassium fertilized treatments experienced greater translocation of sugars from the leaves to the stalks.
Ensuring adequate potassium fertilization of sugarcane increases not only biomass production, but ultimately sugar yield. Higher sugar yield means higher returns. Make certain your sugarcane has access to an adequate supply of potassium.
- Coale, F.J., C.A. Sanchez, F.T. Izuno, and A.B. Bottcher. 1993. Nutrient accumulation and removal by sugarcane grown in Everglades histosols. Agronomy Journal 85:310-315.
- Donaldson, R.A., J.H. Meyer, and R.A. Wood. 1990. Response to potassium by sugarcane grown on base saturated clay soils in the eastern Transvaal lowveld. Proceedings of The South African Sugar Technologists’ Association.
- Hartt, C.E. 1969. Effect of potassium deficiency upon translocation of 14C in attached blades and entire plants of sugarcane. Plant Physiology 44:1461-1469.
- McCray, J. M., H. S. Sandhu, R. W. Rice, and D. C. Odero. 2006. Nutrient requirements for sugarcane production on Florida muck soils. University of Florida IFAS Extension SS-AGR-226.