Investigating reduced nitrogen rates with application of prilled lime

Treatments:

Prilled lime applied @150kg/ha across all treatments.

Three replicates for each treatment:

• T1 91N kg/ha (blue)

• T2 116N kg/ha (pink)

• T3 136N kg/ha (orange)

Lime is applied to bring soil pH closer to neutral and increase calcium levels. It is traditionally applied to the entire block at a rate that is expected to provide amelioration benefits for three years. It is not uncommon for lime to only be applied once per crop cycle.

Prilled lime products use ultra fine calcium carbonate particles that are bound into small prills. The fine particles react quickly with the soil to correct pH while adding calcium. Unlike conventional lime, these products must be applied annually to provide adequate pH amelioration and calcium. They can be easily applied to the cane bed with a standard fertiliser box.

An adequate annual application can address pH issues and calcium deficiency present in the block, preventing run down that can occur over time when lime is applied in one application. As pH moves closer to 6, most nutrients, including nitrogen, become more readily available to the plant (see Figure 2). Maintaining a good pH and providing an adequate supply of calcium throughout the crop cycle is beneficial for crop growth and resilience to stressors, and can maximise the impact of applied fertiliser.

Anecdotally, growers using prilled lime products in ratoon cane had noted a decrease in CCS and wondered if reducing applied fertiliser to account for the improved availability of nutrients applied could benefit their sugar production.

Results There was no significant difference between any treatments for tonnes sugar with variability within the replicates for all treatments. The average tonnes of sugar/ha grown was 18.2-18.3 across the three treatments. This indicates reducing the rate of fertiliser when applying a prilled lime product is unlikely to impact yield. CCS was highest for the 116N treatment and lowest for the 91N treatment. Tonne’s cane/ha was highest for the 91N treatment and lowest for the 136N treatment. However, the difference between these results is not considered significant.

Table 1 (left). Box and whisker chart showing the average and range of tonnes sugar/ha achieved across the three treatments.

Table 2 (left): Box and whisker charts showing the average and range of tonnes cane/ha and CCS achieved across the three treatments.

Table 3 (left): Box and whisker charts showing the average and range of tonnes cane/ha and CCS achieved across the three treatments.