Organic amendments to increase carbon in cropping soils

Year of study:

2012 to 2016

Lead organisations:

Southern Farming Systems (SFS) and Agriculture Victoria


The use of organic amendments on Gippsland Cropping soils will increase the amount of carbon stored in the soil and reduce the need for nitrogen application, while maintaining or increasing production.

SFS Carbon in cropping soils

Trial site details

Trial 1: Giffard

  • Sodosol – loamy sand over heavy, mottled yellow brown clay subsoil
  • In the south western Gippsland cropping region
  • Trent Anderson

Trial 2: Bairnsdale

  • Brown sodosol – sandy loam over heavy sodic clay subsoil
  • In the eastern cropping region of Gippsland
  • Trevor Caithness

Trial site photo

Screen Shot 2015-05-05 at 5.22.51 PM


Trial design layout:

Trial design layout

Experimental Design

Both sites were alike in design, treatments and methodolgy. The design was a replicated complete block design, replicated three times. The treatments were:

  • four rates of chicken litter. 2.5, 5, 10 and 20 tonnes per hectare
  • four rates of compost. 2.5, 5, 10 and 20 tonnes per hectare
  • no organic amendment but with the normal top-dressed nitrogen fertiliser practice regime, matching the amount of N supplied in the 10t/ha compost treatment
  • the control of no organic amendment and no top-dressed nitrogen fertiliser.

The smaller application rates of 2.5 and 5 t/ha were applied annually and the higher rates of 10 & 20 t/ha were a once off application. The amendments were spread with a manure spreader. At each site the same crop type was sown each year with barley sown in the first, canola in the second and wheat in the third year.

Soil and amendment testing was completed annually to be able to determine the application effects of the amendments over time. For each crop yield and biomass data was collected to determine productivity benefits.


Project Outcomes

This project showed:

  • application of compost and chicken litter can increase organic carbon, crop biomass and yield in a cropping system, but found it was not currently economic to do so
  • substantial yield increases by using chicken litter over artificial nutrients
  • application of organic amendments, prior to sowing with no other in crop fertiliser, provides a great opportunity to manage risk, particularly in areas that experience high winter rainfall where top dressing is difficult
  • compost and chicken litter improved water holding capacity of cropping soils and improved plant root growth.

It is hoped that in the future, the economic situation will change, giving the opportunity to use organic waste produced from urban areas and farming industries, producing sustainable soil and productivity benefits to the farming sector and wider community.

Trial work in the future could explore the benefits of supplementing the compost with fertiliser for the first few years to see if the yield penalty can be removed. In the project, yields from the compost treatments lagged behind chicken litter for the first two years. If this was eliminated, it would make it a more attractive option to farmers.

Other questions that have been raised are around the timing of sampling for organic carbon ie: when is the best time to sample to adequately see the changes in organic carbon?

There is also the need to have trials that include organics run for longer than three years. As organic matter takes time to break down, three years may not be adequate time to see the full benefits of the amendments applied.


Analysis of the soil test results taken during the project have given mixed results. For the total carbon, current comparisons of the soil test results from the start of the project in August to the results at the end of the project taken in March, has shown an increase. Alternatively comparing the soil test results taken in April 2013 to the results at the end of the project in March have shown predominately a decrease in total carbon. The possible reasons for the increases are possibly due to the differences in time of soil sampling and that soil carbon is a dynamic parameter, breaking down and increasing over time. This can be seen by the increases in total carbon by the control. Other factors possibly at work are the retention and incorporation of the stubble residues over the three years and the relative newness of the paddocks into a cropping rotation.

Total carbon at 0-10cm at Giffard Park
Total carbon 0-10cm at Kintore
Total carbon at 10-30cm at Giffard Park

The project also looked to demonstrate whether applying organic amendments would reduce the reliance on nitrogen fertilisers and increase crop yields.

  • In year’s one and three of the project when cereals were grown, biomass cuts were taken. In both of those years, the amendments produced higher yields than the treatment (normal fertiliser treatment) that had urea applied. The chicken litter also produced higher yields than the compost. As part of the project the compost and chicken litter were analysed. The analysis consistently shows that chicken litter is giving more nutrient to the crop than the compost which has resulted in large biomass weights.
  • In the first year the crops both sites were sown late and the yields were greatly reduced on the average for the district, especially at Giffard. The results were good at Bairnsdale showing differences between the different treatments. The chicken litter yielded significantly higher that the corresponding compost. The reasons are unclear as nutrient wise they were very similiar but possibly showing differing plant availability.
  • In 2013, Bairnsdale had a very wet June with 200mm above the monthly average falling. The canola crop struggled for many months in wet conditions, only for the season to turn dry. Due to the very wet conditions the canola plants did not develop a normal sized root system and then the crop couldn’t extract sufficient moisture in the dry spring which followed. The result of this was that the yields at harvest were disappointing. Fortunately at Giffard it was wet but not to the same extent and the harvest did give a result. The chicken litter did perform better at the higher rates than the compost and still the 20t/ha of chicken performed better than the treatment which had urea only applied.

At both Giffard and Bairnsdale the yield results suggest in the third year the compost amendments have caught up to the chicken litter. Details are in the table to the right.

This has been supported by other field trials done around the state with the suggestion that perhaps the compost can cause nutrients to be tied up in the short term and may need to be supplemented to overcome this lag. Interestingly the higher rates of amendments were still producing better yields than those that had applications annually.

Wheat yields at Giffard in 2014, the third year of treatments

Means followed by the same letter do no significantly differ (p=0.05).

The Economic Analysis of the project has shown that the results of the trials at Giffard Park and Kintore were significantly different.

At the Giffard Park site, plots with added organic materials at 20t/ha produced more barley, canola and wheat than the Control. All plots with chicken litter amendments produced more canola than the Control. Adding chicken litter and compost at 10t/ha also produced more wheat than the Control.

Trials at Kintore were more positive than at Giffard Park. All treatments produced more barley and wheat than the Control and only Treatment 6 (compost 5t/ha) and Treatment 8 (compost 20t/ha) did not produce more canola than the Control.

At Giffard Park, plots with chicken litter amendments at 20t/ha produced more grain when compared with Normal plots. For both canola and wheat crops, the addition of chicken litter at 5t/ha and higher generated additional grain production than Normal. At the Kintore trial site, all organic material treatments produced more barley than Normal. However, canola production from plots with amendments did not do well when compared with ‘Normal’ plots.

Since the extra costs of adding organic materials did not cover the extra production if there was any, all plots at the Giffard Park site had negative Net Present Values when compared with the ‘Control’ and ‘Normal’ plots.

At the Kintore site, among the plots with organic matter amendments, only Treatment 5 (compost 2.5t/ha) posted a positive Net Present Value of $77/ha when compared with ‘Control’. When compared with ‘Normal’, Treatment 5 (compost 2.5t/ha) and Treatment 7 (compost 10t/ha) generated positive Net Present Values of $27/ha and $77/ha respectively. For these treatments, the additional expense on compost was justified because the value of the extra production covered the extra costs.

The economic analysis showed that the application of organic materials in the form of chicken litter and compost was not economic at the Giffard Park trial site (table 1 and 2). The application of compost at 2.5t/ha and 10t/ha was economic at the Kintore site.

Table 1. Net present value at 10% discount rate, Giffard Park and Kintore sites. Treatment vs. control

Table 2. Net present value at 10% disocunt rate, Giffard Park and Kintore sites. Treatment vs. normal

2016 additional year

Continued the 2.5 and 5t/ha treatments sites for a fourth year, (just at Giffard site) to determine if the application of organic amendments over time have the same impact as a once off application of 10 and 20t/ha and to look at carbon levels.

The variation for the fourth year was that conventional fertiliser as per normal farm practice, was applied across all treatments.

Results show that the total carbon is on the rise again and for a number of treatments back up to the levels in April 2013, overcoming the issues that had held it back in the previous year.

Figure 1. Comparison of total carbon levels in the control, normal fertiliser and the chicken litter treatments at 0-10cm.

Figure 2. Comparison of total carbon levels in the control, normal fertiliser and compost treatments at 0-10cm.

Figure 3
Figure 4

Figure 3: Comparing the organic carbon percentage for each treatment over time at 0-10cm.

Figure 4: Comparing the organic carbon percentage for each treatment over time at 10-30cm.


After 4 years the amendments that had been applied at the start had no increase in yield compared to the control.

This can be seen in the table to the right and in figures 5 and 6. There was also little effect on the yield by the fourth year.

Table 2 Treatments yields

Table 2: Treatment yields for 2015.

Means followed by the same letter do no significantly differ (p=0.05)

The economic study completed as part of the AOTG project indicated that the application of organic materials in the form of chicken litter and compost was not economic at this site. Due to the harvest results this would still be the case after the fourth year.

Figure 5 Yield difference
Figure 6 Yield difference

Figure 5: Yield difference. Compost treatments compared to control and normal fertiliser treatments.

Figure 6: Yield differences. Compost treatments compared to control and normal fertiliser treatments.


Many thanks to the Anderson family at Giffard for allowing the compost project to continue on their farm.

Year 1 to 3 of this project was funded through the Australian Government’s Action on the Ground Programme.

Year 4 was supported by the West Gippsland CMA through funding from the Australian Government’s National Landcare Programme.

WGCMA logo
Agriculture Victoria logo

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Findings and views expressed in the Gippsland Soil Trials and Demonstrations pages are those of the proponents. The scope, objectives and scientific rigour of the information varies greatly. The intention is to provide a repository of information that facilitates discussion.

3 thoughts on “Organic amendments to increase carbon in cropping soils

  1. Thanks for sharing the work. Is it possible to get a break down of the economic analysis ?
    Whats the origin of the compost ?

    1. Hi Michael, The compost came from a very large Soils and Organic Recycling Facility (SORF) managed by Gippsland Water at Dutson Downs. The facility is producing massive quantities of blended compost from a variety of sources and also offers compost mixed with lime and or synthetic fertiliser. For more details on the trial you would need to contact Janice Dowe from Southern Farming Systems – Gippsland Branch.

  2. Thanks for the info. As with trials more questions appear. eg what if microbes where applied? . Agree that longer time frame is required.

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