Farming for the future: optimising soil health for a sustainable future in Australian broadacre cropping
Author: Alexander Nixon, Nuffield Scholar, Drillham, Qld | Date: 01 Aug 2019
Take home messages
- Observations from overseas are that incorporating multi-species cover crops is an effective and efficient means to improve soil function and health
- Multi-species cover rotations are a financially viable option for Australian broadacre cropping operations seeking to improve their soil and reap the subsequent benefits through increased cash crop yields
- Careful planning and management of the rotation schedule and seed-mix selection is required to optimise benefits.
For many years conventional farming practices have been degrading the state of our soils. The zero-till farming revolution has instigated a push towards improved soil health. New research indicates that bio-diversity and groundcover are essential contributing factors to optimal soil health, and many farms in the USA and England have been implementing multi-species cover crop rotations in conjunction with zero-till practices with amazing results in soil rejuvenation and increased cash crop yields. The sustainability of Australian broadacre dryland cash cropping operations, and the agricultural industry in general, hinges heavily on a soil health focus. Incorporating multi-species cover crops into cash crop rotations is the most effective way to improve soil health.
Cover crops for ground cover
Maintaining ground cover is essential to soil health on multiple levels. As the name implies, cover crops aim to achieve exactly that. They are intended to be sown after the completion of a cash crop, in place of long-fallowing. Cover crops are typically left to grow until the milky stage of seed production, or until sufficient biomass has been obtained, after which point, they are terminated – usually either lightly tilled in, mowed or rolled/crimped or sprayed – with the residue remaining as ground cover. Weed suppression, prevention of erosion, increased soil organic matter (SOM) levels and improved water infiltration/moisture retention, can potentially be achieved by cover cropping.
Soil function and bio-diversity through multi-species cover crops
The soil ecosystem is complex with many aspects of soil chemistry and physics are inter-related. Plant bio-diversity has proven to be a key factor when considering soil health, as different plants serve a variety of purposes both above and below the soil surface. Maintaining a diverse range of plant roots aids in preserving an array of different microbe communities and helps sustain the balance between fungi and bacteria, and also moderates the Carbon:Nitrogen (C:N) ratio. Concurrently, different plant types achieve varying degrees of cover on the soil surface and each species contributes in different ways to both the carbon and nutrient cycles. Species diversity is valuable to soil health due to its reliance on a range of functions which are often heavily inter-connected and overlapping.
Financial viability of cover crop rotations in broadacre dryland farming
Optimal soil health is important to future sustainable and financially viable broadacre cropping. Multi-species cover crops are a method for rejuvenating and maintaining soil conditions. However, broadacre dryland farming businesses face several issues when moving towards such conservation management practices. Firstly, upfront costs of cover crop seed currently remain high. Machinery investments, such as rollers, mowers or crimpers are costly and are not yet readily available in Australia. The logistical implications associated with the scale of Australian farms could incur increased expenses. And finally, business cashflow can become compromised if input costs to establish the cover crop exceed the expected returns for the season.
Logistics and considerations
Most research, trials and recommendations for implementing cover crops currently stems from the USA. When considering applying this knowledge to Australian broadacre cropping systems the information must be adapted, though many of the basic theories remain the same. Factors for consideration include, but are not limited to:
- Soil type
- Current management practices
- Existing cropping schedules.
Species selection is perhaps the most important element to successful cover cropping. Several factors must be considered when choosing a cover crop mix, being:
- Current soil conditions – soil testing prior to seed mix selection is advisable to establish what functions are required and thus which species can best fulfil the requirements
- Subsequent cash crop – it is important to keep this in mind to avoid any potentially negative impacts from undesirable soil changes or pathogenic species to the following crop. Varieties selected must be compatible together, and with the subsequent cash crop
- Seasonal and climatic conditions – rainfall, temperatures and time of year should all be considered when choosing each variety for a multi-species cover
- Plant functional group – a selection of cereals, grasses, legumes, brassicas and chenopods is recommended for optimal soil health benefits.
The effectiveness of incorporating cover crop rotations for rejuvenating and maintaining soil has been substantiated in many farming situations around the globe. Research for this report was conducted on several properties in the USA and England, with notable success in restoring soil health recorded at each. However, one common concern was the financial viability while transitioning to this management practice. A business, or business decision, is considered financially viable when generated income exceeds costs.
Another important point to note is the relative size and scale of the business. Some of the farms visited were as small as 600 acres (approximately 243 hectares), while the average farm size in Australia is 4,331 hectares (Australian Bureau of Statistics, 2017). Appropriating business funds for cover-cropping to such a scale as to fit the average Australian farm, could initially pose the following issues and risks:
- Increased upfront costs for seed and planting
- Compromised business cashflow
- Time allotted for planting/termination could result in the necessity for multiple machines to be operating to achieve the task within ideal timeframes, resulting in more business funds being absorbed by capital investments
- Soil types can vary dramatically from one end of a largescale paddock to another, impacting cover-mix selection and effectiveness.
Some suggestions to alleviate and manage these problems are to:
- Start small – one paddock at a time
- Consider frequency and size of cover rotations based on benefits produced, and increase accordingly over time
- Consider value-adding - Controlled grazing of cover crops can provide extra income/soil benefits over the cover-crop season. Investing in livestock or offering short-term agistment are two potential options.
While some financial difficulties may arise when farming operations initiate cover-crop rotations, the long-term monetary benefits are purportedly profitable. Some of the economic benefits of multi-species cover cropping are:
- Decreased fertiliser costs
- Reduced requirement for herbicides and pesticides
- Higher yields – due to improved soil health.
The sustainability of Australian broadacre dryland cash cropping operations, and the agricultural industry in general, hinges heavily on a soil health focus. Incorporating multispecies cover crops into cash crop rotations is a way to improve soil health.
The evidence presented in this report demonstrates that multi-species covers can alleviate several environmental factors affecting soil health by:
- reducing or preventing erosion
- increasing water infiltration
- inhibiting weed growth
- stabilising losses of or increasing soil organic matter.
Further, this report emphasises the importance of bio-diversity within a cover crop, showing how a species-rich environment creates synergy between multiple soil components. Bio-diversity encourages:
- effective carbon and nutrient cycling
- a balance of C:N ratios
- microbial growth and activity
- healthy bacteria to fungi ratios.
Though implementing diverse cover-crops can pose initial economic issues, the long-term environmental and economic benefits prove to outweigh the financial deficit associated with the transition phase. Through careful management and mix-selection, multi-species cover cropping can certainly be a viable option for Australian broadacre farmers seeking to improve soil health.
- Employ zero-till farming practices wherever possible to lessen soil degradation.
- Create a cover crop rotation schedule – based on soil test results and current cash crop rotations. It is imperative to have a plan, goal and strategy in place in order to be effective and efficient in any business venture.
- Implement a business plan for the transition phase – expect that multi-species cover cropping is a long-term investment, interim alternative income sources may be required to support the associated expenditure.
- Conduct regular soil testing – knowing your soil and monitoring soil changes will ensure that appropriate actions can be taken e.g. which paddocks require attention, what soil health issues are arising, and which plant species are most suited for rectification.
- Research plant varieties suitable for the region – understanding species for both their benefits and their required growing conditions is advisable. Consider contacting a local agronomist if necessary and remember, the more species the better!
- Construct a “seed budget”. Seed will be the primary input cost. Pricing different varieties and options available and adhering to a budget will minimise any negative financial impacts in the initial season.
- Decide which methods will be employed for planting and termination – performing an opportunity cost analysis may assist when considering alternatives.
- Consider value-adding (such as livestock grazing). It is important to closely monitor and control any grazing to ensure the best results from plant growth benefits.
- Encourage neighbours to get involved – a local cooperative initiative could be an option for capital investment of plant and machinery, bulk seed purchases to obtain discounts and disseminating local knowledge, information and findings from trials.
- Consider applying for government grants and subsidies associated with agricultural conservation practices.
This Update paper contains excerpts from the author’s Nuffield Scholar Report. The unabridged report is available here.
I would like to thank the GRDC for sponsoring my scholarship, and Nuffield Australia for the opportunity.
Bexa Pty Ltd T/A Devon Court Stud
769 Wallan Creek Road
Drillham Qld 4424
Mb: 0429 432 467
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