Polysulphate sweetens sugarcane production

The importance of sugarcane for rural economies

Sugarcane is a significant crop for the tropical and sub-tropical regions of the world. In India, the second largest sugarcane producer after Brazil, 74% of production is concentrated in just three states, Uttar Pradesh, Maharashtra, and Karnataka. The sugar industry in these regions contributes significantly to the rural economy, providing large-scale employment for many rural areas.

Nutritional needs of sugarcane

While India is the second largest producer globally, it struggles to match other countries’ productivity. Sugarcane is a high-performance perennial plant that produces multiple tall stems each year. These stems can grow up to 6m tall. Achieving this growth in a year takes warmth, water, and the correct balance of nutrients. But it is not just the size of the cane plants that is important. Sugar content is the main factor affecting the value of sugarcane crops, and sugarcane plants need sufficient potassium to achieve higher sugar content. Plants require potassium for many aspects of their development and growth. But for sugarcane, potassium’s role in the production and accumulation of sugars within the plant is critical.

Delivering the correct nutrition

So, armed with this knowledge, we see that growers need to apply a potassium fertilizer, right? Well, that is right, but it is a bit more complicated than that. A recent paper published in the scientific journal Research on Crops (volume 24) describes a sugarcane trial that explores the nutrient requirements of sugarcane and how different sources of these nutrients affect yield. In particular, the researchers tested whether using polyhalite instead of muriate of potash (MOP) as the source of potassium makes a difference.

Polysulphate as a fertilizer

Polyhalite is the natural mineral that ICL mines in Boulby in the UK. This natural mineral is crushed, screened, and sold as Polysulphate fertilizer. Polysulphate supplies sulfur, potassium, magnesium, and calcium, all in sulfate form, and benefits from a natural, prolonged release pattern that delivers nutrients throughout the growing season.

Testing research

The research tested ten treatments using a randomized block design with three replicates on a farmer’s field in Tamil Nadu, India. Each treatment (shown in the table) received nitrogen and phosphorus at the recommended fertilizer dose (RFD). The total potassium application was either 50, 100, or 150% of the recommended fertilizer dose, delivered as MOP, Polysulphate, or from a combination of the two sources.

Clear results

The results are convincing. Throughout the growing season, the researchers examined 13 distinct criteria to measure any difference in sugarcane growth between the treatments.

• plant height,
• number of leaves per stalk,
• leaf area index,
• leaf chlorophyll content,
• number of internodes per stalk,
• length of internode per millable cane,
• length of the millable cane,
• diameter of millable cane,
• single cane weight,
• number of tillers per plant,
• number of millable canes,
• cane yield, and
• sugar yield

Looking at the results, we see a similar pattern for each of these measurements. The control treatment, which received the recommended dose of nitrogen and phosphorus but no potassium, was the worst. As the potassium application increases, the sugarcane improves. The treatments that received 150% of the recommended fertilizer dose had the best results. But the results show that the potassium dose is only part of the equation. At each potassium dose, the plants which receive a greater proportion of the potassium from Polysulphate perform even better.

Influence of Polysulphate on cane yield of sugarcane (% shows increase compared to T₃).

Influence of Polysulphate on sugar yield of sugarcane (% shows increase compared to T₃).

Maximizing sugarcane yield

What is particularly interesting about the research paper is how it demonstrates that the maximum values for the growth parameters, and ultimately for the yield attributes, were not just achieved with the higher potassium doses but specifically in the treatments where the sugarcane received 100% of the potassium from Polysulphate. Sugarcane growers would do well choose Polysulphate to improve their sugarcane yields.