Agronomic principles for sugarcane

As a C4 plant, sugarcane has a very high rate of photosynthesis - around 150-200 % above the average of other plants. Crops progress through tillering to a period of grand growth. This phase of rapid growth needs to be supported by a comprehensive nutritional program.

The first planting - or plant crop – is normally derived from a small length of cane called a sett or billet, some countries plant whole sugarcane. The buds or eyes on this sett germinate to produce shoots and roots which establish the first season’s crop. In some cultivars, roots develop first and in others, shoots. 

Season and crop length varies according to climate and variety and ranges from 12 to 24 months.

After the first planted sugarcane has been harvested, a series of successive crops - called ratoons - develop from this stool or stubble. As each new ratoon crop develops, the old roots die and new ones are formed. New tillers are also generated and from these the next season’s cane sugar is harvested. 

After each successive year, dry matter production and sugarcane yield gradually declines. In some circumstances, due to significant disease pressures and limited availability of suitable varieties, e.g. in some Asian countries, crops are replanted every other season.

Planting Practice 

Planting is an important operation as it helps determine the number of ratoons across the life of the crop. Cane is cut into setts or billets which are ideally 30 cm in length and generally have three or four eyes. 

In some countries whole canes are planted. Billets are overlapped and planted in long furrows or trenches at 15-30 cm depth. Spacing should be between 10,000 to 15,000 setts/ha to provide an optimum density of 90,000- 150,000 stalks/ha at harvest. 

In the past, row spacings have commonly been around 1.5m, but the industry is moving towards matching row spacing to machinery wheel spacings at 1.8-1.9m centers with no loss of sugarcane yield. This helps to maximize yields by reducing compaction in the soil and minimizing damage to the stool. 

Where waterlogging is an issue, permanent drains and/or raised permanent beds are used. Sett quality is very important and growers should use seed cane that is disease free and in good condition with eyes that are damage-free. Cane used for planting is often produced in defined areas of the farm where good disease and pest control is practiced and adequate nutrition is provided. Cutting knives should be dipped in disinfectant to minimize the spread of diseases such as Ratoon Stunting Disease (RSD) in the new setts.

Trash forms a blanket over the soil after harvest. This can have some significant advantages – for example, it acts as a mulch to suppress weeds, conserves moisture for the ratoon crop and limits soil erosion. Usually this trash has broken down during the growing season and before the next harvest.

Switching to a green cane harvesting system can improve yields, largely as a result of improved organic matter, nutrient status and soil structure, along with reduced erosion, moisture conservation and weed suppression.

Mill By-products

Bagasse

Bagasse is the fibrous material that remains after sugarcane is crushed. Typically, for every 10t of cane that is crushed, 3-4t of wet bagasse remains. It has a high moisture content – typically 40 to 50% - and is usually stored prior to further processing. Increasingly it is used as a fuel for steam and electricity generation at the mills, but it is also a source of organic matter when returned to soils.

Ash and filter mud

Ash and filter mud are also used as a fertilizer. Boiler ash is ‘scrubbed’ from the mill stacks and filter mud/cake is the residue left after the sugar has been clarified. Filter mud/cake can be used to improve soil organic matter and boost soil nutrient levels. It is often used for compost together with bagasse.

Vinasse

Vinasse is a residue from the alcohol distillation process. It contains high levels of organic matter, potassium, calcium and moderate amounts of nitrogen and phosphorus. Care is needed in handling vinasse as it can be corrosive. In some countries vinasse is concentrated by means of evaporation and is called CMS (Concentrated Molasses Solid).

The nutrients applied using these mill by-products need to be taken into account when devising fertilizer programs for sugarcane.