Sub-surface fertiliser application reduces nutrient runoff in the Herbert

Key findings

• Sub-surface fertiliser application reduced runoff losses of nitrogen, phosphorus and sulphate-S from recent applications when compared to surface application.
• The presence of cane trash reduced the runoff loss of nitrogen, phosphorus and sulphate-S from recent applications when compared to trash removal.
• The improved practice of sub-surface fertiliser application increased yield (total sugar per hectare) over broadcast application and reduced the runoff nutrient loss.

About this case study

The application of fertiliser provides essential nutrients to enhance sugarcane growth and yield. The rate of application is important. Similarly the type of fertiliser (e.g. granular versus liquid) and where the fertiliser is placed in the soil profile can influence plant uptake and the loss through run off and deep drainage.

The objectives of this rainfall simulation study were to:

• measure the effectiveness of sub-surface fertiliser application in reducing the amount of nutrients lost in runoff compared to surface application
• measure the effectiveness of liquid fertiliser application in reducing the amount of nutrient lost in runoff compared to granular application
• measure the impact of trash retention practices on nutrient loss
• measure the impact of different fertiliser practices on yield
• provide nutrient runoff loss data to enhance predictive modelling of the effectiveness of improved management practices.

Methods

Fertiliser was applied to ratoon cane in two field replications using traditional and improved application practices. Trash was removed from selected plots one day prior to the application of the fertiliser treatments. Seven days after fertiliser application each plot (1.7 metres long by one metre wide centred over the cane row) received simulated rainfall (average 77 millimetres per hour) until runoff commenced and then for a further 30 minutes. Samples were collected during the runoff event to determine runoff rate and nutrient concentration in runoff.

Results

• Sub-surface fertiliser application reduced the nitrogen, phosphorus and sulphate-S runoff loss by over half compared to surface application. Trash retention also reduced the runoff loss in surface applications.