• Mill by-products (mud, ash and mud-ash mixtures) are effective ameliorants and a source of several nutrients required by the sugarcane crop.
  • These nutrients are in both organic and inorganic forms and availability to the crop will be influenced by seasonal conditions as well as soil-specific factors.
  • The nutrient content of mill by-products also vary from season to season, mill to mill and even among individual loads, making assessment of nutrient application rates across a block or farm potentially quite variable.
  • Nevertheless, nutrient management plans should take the application of mill by-product into account and nutrients rates adjusted to account for the nutrients applied.
  • The SIX EASY STEPS uses estimates of how much nutrient in mill by-products is available to the crop in order to allow for product variability and nutrient availability issues.
  • When mill by-products are applied at rates below 100 wet t/ha the nutrients they contain do not need to be accounted for in Reef Regulations (refer to “Farming in Reef catchments – Prescribed methodology for sugarcane cultivation”). However, there is an opportunity to adjust nutrient management plans to account for the nutrient content in mill by-products even at these low application rates.
  • If nutrient rates are not adjusted, there is strong evidence that CCS is reduced when mill by-products are applied.

Determining rates after mill by-product applications

The table below indicates the quantity of nutrient (kg/ha) in a typical application of mill mud, ash and mud-ash. It is important to remember that nutrient quantities can vary considerably. Values are rounded where appropriate.

Plant nutrient

Mill or Filter mud

(100 t/ha)

Mud-ash mixture

(100 t/ha)

Ash

(100 t/ha)

Nitrogen (N)

310

240

40

Phosphorus (P)

240

200

80

Potassium (K)

80

130

260

Calcium (Ca)

430

400

290

Magnesium (Mg)

90

110

150

Sulfur (S)

55

35

65

Copper (Cu)

4

3

3

Zinc (Zn)

13

11

9

Manganese (Mn)

125

120

95

Silicon (Si)*

3500

5000

21500

Moisture content

~75%

~75%

~50%

 

*Mill ash contains a large proportion of silicon but much of it is unavailable for plant growth. However, there is sufficient available silicon to rectify a soil deficiency, making it one of the more useful sources of silicon for sugarcane crops.

 

  • Mill mud consists of water, fibre, soil, and soluble sugars and proteins from within the sugarcane stalk.
  • Mill mud also contains lime that has been applied during the clarification process in the sugar mill.
  • Mill mud contains many of the essential nutrients required by a sugarcane crop including; nitrogen, phosphorus, potassium, calcium, magnesium and sulfur.
  • While mill mud contains large quantities of some of these nutrients, the total may not be immediately plant available as they are present in organic forms (particularly nitrogen) and require mineralization by soil organisms before plant uptake can occur.

Modifications to nutrient recommendations following mill mud application at 100 wet tonnes/ha

Mud

Estimated reduction to nutrient rates (kg/ha)

Nutrients

1st crop

2nd crop

3rd crop

Nitrogen

55

30

10

Phosphorus Sufficient P for 1 crop cycle*
Potassium

25

0

0

Sulfur

5

5

5

Calcium Reduce Agricultural lime by 1.3 t/ha or gypsum by 1.6 t/ha
Magnesium Sufficient Mg for 1 crop cycle except where severe deficiency exists

*Soil testing after the first crop cycle should guide P fertiliser rates in the following crop cycle.

 

  • Mill ash is generated from the burning of bagasse and, in some cases, coal in the sugar mill’s boilers.
  • Mill ash is a useful ameliorant of sodic soils (see sodic soils tool).
  • Mill ash contains several essential nutrients required for sugarcane growth, and is a particularly useful source of high quantities of potassium and silicon.
  • It contains approximately 43% silicon (on a dry weight basis) although not all is available for plant uptake.

 Modifications to nutrient recommendations following mill ash application at 100 wet tonnes/ha

Ash

Estimated reduction to nutrient rates (kg/ha)

Nutrients

1st crop

2nd crop

3rd crop

Nitrogen

0

0

0

Phosphorus

Sufficient

Check with leaf test

Check with leaf test

Potassium

80

80

0

Sulfur

0

0

0

Calcium Reduce Agricultural lime by 1.3 t/ha or gypsum by 1.6 t/ha
Magnesium Sufficient Mg for 1 crop cycle

 

  • Mud-ash mixtures are a useful ameliorant of sodic soils (see sodic soils tool).
  • Mud-ash mixtures are a rich source of essential nutrients.
  • In some areas only mud-ash mixtures are available and are highly variable due to the mixing process in the mill.
  • Mud-ash mixtures contain approximately 20 % silicon (on a dry weight basis) although not all is available for plant uptake.

Modifications to nutrient recommendations following mill mud/ash application at 100 wet tonnes/ha

Mud/ash mixture

Estimated reduction to nutrient rates (kg/ha)

Nutrients 1st crop 2nd crop 3rd crop
Nitrogen

35

10

5

Phosphorus Sufficient P for 1 crop cycle*
Potassium

80

0 (80 in NSW only)

0

Sulfur

5

5

0

Calcium Reduce Agricultural lime by 1.3 t/ha or gypsum by 1.6 t/ha
Magnesium Sufficient Mg for 1 crop cycle except where severe deficiency exists

*Soil testing after the first crop cycle should guide P fertiliser rates in the following crop cycle.

 

  • Mill by-products should be banded on or in the crop row.
  • Banding mill by-products concentrates the applied nutrient in the region where sugarcane roots can access them, particularly if the banding is sub-surface.
  • Leaf testing should be used to confirm adequate nutrient levels in the crop.
Mud

50 t/ha banded

Estimated reduction to nutrient rates (kg/ha)

Nutrients

1st crop

2nd crop

3rd & 4th crop

Nitrogen

25

15

0

Phosphorus

Sufficient

Sufficient

Sufficient

Potassium

15

0

0

Sulfur

0

0

0

 

Mud-Ash

50 t/ha banded

Estimated reduction to nutrient rates (kg/ha)

Nutrients

1st crop

2nd crop

3rd & 4th crop

Nitrogen

15

0

0

Phosphorus

Sufficient

Sufficient

Check with leaf test in 3rd crop

Potassium

40

0

0

Sulfur

0

0

0

 

Fine tuning nutrient rates following the application of mill by-products

  • Any change in nutrient management should be tested on-farm. This will build confidence in both the new nutrient rates but also the process of fine tuning a nutrient management program as part of steps 5 & 6 in the SIX EASY STEPS.
  • A guideline for conducting on-farm trials is included in the SIX EASY STEPS toolbox.
  • Leaf testing also provides a valuable method for checking on the adequacy of nutrient inputs.

Disclaimer:

Papers published from the Australian Society of Sugar Cane Technologists annual conference are also available at www.assct.com.au

 

Version: April 2020

 

Disclaimer: In this disclaimer a reference to ‘SRA’, ‘we’, ‘us’ or ‘our’ means Sugar Research Australia Limited and our directors, officers, agents and employees. Although we do our very best to present information that is correct and accurate, we make no warranties, guarantees or representations about the suitability, reliability, currency or accuracy of the information we present in this publication, for any purposes. Subject to any terms implied by law and which cannot be excluded, we accept no responsibility for any loss, damage, cost or expense incurred by you as a result of the use of, or reliance on, any materials and information appearing in this publication. You, the user, accept sole responsibility and risk associated with the use and results of the information appearing in this publication, and you agree that we will not be liable for any loss or damage whatsoever (including through negligence) arising out of, or in connection with the use of this publication. We recommend that you contact our staff before acting on any information provided in this publication. Warning: Our tests, inspections and recommendations should not be relied on without further, independent inquiries. They may not be accurate, complete or applicable for your particular needs for many reasons, including (for example) SRA being unaware of other matters relevant to individual crops, the analysis of unrepresentative samples or the influence of environmental, managerial or other factors on production.