Diversity key to successful systems: how far can you copy the natural ecosystem?
GroundCover™ Issue: 33
This is an abridged version of an open letter from Dwayne Beck, Professor of Crop Agronomy, South Dakota State University, first published in the Western Australian No-Tillage Farmer Association (WANTFA) May 2000 newsletter. Professor Beck has advised WA no-tillage advocates for a number of years and was a keynote speaker at the WANTFA 2000 annual conference.
The order used to discuss the following issues has no relationship to their importance. In a weak-link analysis or systems approach, their relative importance will vary among producers.
Soil and climate
The first issue that needs to be addressed is the difference between your soils and our soils. Prairie soils are wonderfully forgiving living organisms. They have taken substantial amounts of abuse over the last 80-100 years and yet still remain reasonably productive. Australian soils are not as resilient.
They are older and more fragile, and consequentiy it is more important that they be managed properly. In other words, the fact that Australian soils are different from prairie soils is a major reason why they should be managed in a sustainable manner. Failure to do so will lead to far greater and far more rapid productivity losses than we would ever experience with our prairie soils.
As well as this, there are major differences between our climates. This does not mean that basic biological principles change when we cross the equator. The principles are the same, but they must be applied to different (both favourable and unfavourable) weather conditions.
The approach used at the Dakota Lakes Research Farm has always been to attempt to understand how basic biological principles work in our [native] ecosystem, and then to design farming systems that match the plant diversity, water use, and nutrient cycling of the ecosystem as closely as possible.
We believe this approach has substantially decreased the amount of time it would take to develop sustainable systems using more traditional methods. As with the soils issue, I would agree that it is probably easier to emulate a prairie ecosystem with annual crops than it is to mimic the ecosystem that you call 'the bush'.
The European cropping systems brought to North America by my ancestors did not work in a prairie ecosystem, so we certainly cannot expect them to work in the Australian climate.
Natural water cycles
Many of the problems being experienced in WA appear to be as a result of not matching natural water cycles. The most obvious symptom of low water-use efficiency is the dramatic increase in salinity that has occurred in the four years since my last visit.
Many of the present approaches to dealing with salinity fall into the category of treating the symptom (salt) rather than the cause (inefficient water cycling). The construction of drainage ditches and the sowing of salt-tolerant species in low-lying areas merely treat the symptom.
The cause of the problem is water in the upper landscape not being cycled properly. Applying water-use management strategies to the lower landscape does nothing to stop the loss of nutrients (and soil acidification) associated with the 'leakage' in the system. The expense of building the drainage system, in my opinion, will pale in comparison to future expenses associated with taking this approach.
Also included will be costs associated with increased regulation of agricultural inputs because they will certainly be detected in the drainage water. Having nutrient or pesticide concentrations in drainage water at lower levels than current standards, or than what is already in a stream, will not be good enough in the future.
It will have to be as low as would occur if agriculture were not present. Those who question this happening should review the history of the Kesterson Reservoir in California and the more recent issues surrounding the growth of the hypoxic zone in the Gulf of Mexico.
Limits to tree-planting strategies
Planting trees in strips or along contour banks in the upper landscape partially addresses the problem of utilising the water in these landscape positions. There are two issues that limit the long-term viability of this approach. The first is that trees limit efficiency in farming operations and create an environment where weeds, diseases, insects, animals, birds, and the trees themselves from these strips may negatively impact the cropped areas between them.
A more long-term concern is that these tree rows will accumulate the nutrients from the inter-row areas into the biomass and soil in the strips where it is not free to cycle to the crop.
Strategic planting of trees for water use is better than allowing it to accumulate in low areas or drain to the ocean, but it is less than ideal.
The only way that trees could make more efficient use of available water would be if the natural bush was 'copied' to a certain extent, and trees were established as the dominant species on [some] landscapes. This approach would have a profound impact on farming communities, small towns and agribusiness, unless it was limited to critical areas, or involved trees that have [commercial] value on an annual and ongoing basis — still a last resort.
Salinity requires a mix all Year long
The ideal solution for salinity control and nutrient cycling is to have a mix of crops that cycle the nutrients and water on all areas of the landscape. The nutrient and water-use efficiency must be fixed in order for the farming system to be sustainable.
This will require the use in the mix of some species that grow in the warmer times of the year over all areas in the landscape (not just the recharge areas). This may take the form of perennial sequences (like lucerne), warm-season annuals (like safflower, sorghum, forage sorghum),warm-season cover crops, or some combination of these approaches. Warm-season crops will become a part of die rotation, and will help improve water-use efficiency (water cycling) and long-term profitability. Growing warm-season crops as a cash generator is a noble goal, but in the short run some producers may not be able to make this happen.
Their use should first be viewed as a way of reducing the cost of producing traditional crops by stabilising the system. I have no doubt that, with more research and farmer experience, ways will be found to produce these crops profitably.
Determining how to balance water use while maintaining short-term profitability will be the biggest challenge facing producers. Covering all the potential strategies that could be tried goes beyond the scope of this article. The fact that the sorghums and cotton were behaving as perennials in several locations we visited indicates that they may be much better at cycling deep water and nutrients than would be expected if they behave'd as annuals.
Resistant weeds and rotations
The other issue that needs to be addressed is resistant weeds. Herbicide resistance is a symptom of rot聡tions that are not sufficiendy diverse. Other symptoms of this lack of diversity include many of the disease and insect problems that are occurring.
There probably is time in most cases to clean up the problems if steps are taken to diversify the cropping rotations, increase competition, reduce disturbance, and limit movement of resistant biotypes from one paddock to another.
In short, every effort must be made to reduce the selection pressure exerted by the herbicide program. Short rotations make the selection pressure both predictable and frequent. Companies are not producing any new magic. Even if they were, the same fate would result unless the selection pressure is reduced.
No-one paid much attention in 1996 when we proposed that ryegrass would develop resistance to the chaff cart technique. That happened first with the development of early-shattering lyegrass. This required the use of swathers in conjunction with the carts. The next step will be the development of a lodging biotype that will escape the swather. The point is, if you provide a predictable opportunity, certain species will develop a predictable response by utilising that opportunity.
Variation on the theme
Growing crops with varied seeding dates removes the predictability from the system. Stacking crop types within rotations will allow use of both long and short residual programs to vary selection pressure and reduce the frequency of application of any given mode of action. High-disturbance systems negate some (if not most) of the value of these approaches.
Efforts need to be made to determine how to handle problems such as root diseases and 'tillage responsive soils' in alternative ways, so that low-disturbance techniques can be employed. With good rotations, root diseases disappear. What about tillage on tillage-responsive soils? Find a way to provide that without the tillage.