A Revolution in Land Use
Options and future prospects – part 1
Annual cropping
Joint Venture Agroforestry Program
Opportunity cropping
Phase farming
Companion farming
New agricultural plants
Redesigning Agriculture for Australian Landscapes
Organic farming
Annual cropping
Most of the Basin with rainfall greater than 400 mm has been cleared for
agriculture, predominantly for annual crops and pastures. In this section
we present an overview of the expected leakage of water below annual crops
across the Basin. The estimates below are from field-calibrated simulation
modelling of annual cropping, but the same principles apply to annual plant-based
pasture systems.
Two transects are explored (Figure 8). The first considers the amount
of rainfall; the second the timing of rainfall. These simulations are
for a deep well-drained soil using weather data collected over the past
40 years.
Figure 8. Simulations were carried out across N–S and E–W
transects.
The E–W transect runs across the Basin at approximately 33oS, taking
in towns such as Condobolin, Parkes and Orange. Annual rainfall ranges
from 320 mm in the west to 870 mm in the east. Rainfall at this latitude
is slightly winter dominant (55% of the annual total).
The estimates of average annual leakage for a wheat cropping system increase
from almost nothing in the west to well over 200 mm in the east (Figure
9). The simulations also show that higher input farming has had a large
effect on yield, but not on drainage. Doubling nitrogen fertiliser (N)
from 40 to 80 kg/ha increased yield by 20–40% but only reduced annual
leakage by about 25 mm (Figure 9). Bigger crops with more leaves mean
more transpiration and interception, but this is largely at the expense
of soil evaporation, not leakage below the root zone.
Figure 9. Predicted leakage with increasing rainfall along the E–W
transect for a range of current land-use options and future prospects.
The N–S transect, which explores the impact of winter and summer
rainfall dominance, runs roughly along the 575 mm rainfall isohyet (range
550–600 mm), extending from Roma in Queensland, through Moree, Dubbo
and Parkes in New South Wales, and ending with Rutherglen and Bendigo
in Victoria. The proportion of annual rainfall received in the winter
months increased from 40% in Queensland to 70% in Victoria.
The N–S transect highlights the influence of winter-dominant rainfall
on leakage (Figure 10). As winter dominance increases, so too does the
leakage associated with annual cropping. This is because more of the rainfall
occurs in the cooler part of the year, when potential water use by vegetation
and loss via soil evaporation is reduced.
While the targets for leakage will need to be specific to catchments
or landscapes, they are almost certainly well below 20 mm/y. Therefore,
based on these simulations and complementary experimental work, annual
cropping systems fall a long way short of acceptable leakage targets.
Yet some would argue that this is not the last word.
There has been continuous change in farming systems since the land was
first cleared. In trials across southern NSW, wheat crops grown under
practices common in the 1990s were compared to a best management package
that included disease-break crops or nitrogen top-dressed crops. The better
managed crops had higher yield and also left the soil around 20 mm drier.
Such improvements are in line with model predictions shown in Figure 9,
and again fall short of what is required over most of the cropping zone.
The best hopes for cropping systems are to concentrate on soils with
high water-holding capacity, and to introduce summer crops or perennial
pastures into rotations according to the amount of water stored in the
soil.
Figure 10. Predicted leakage with increasing winter dominance for
a range of current land use options and for future prospects (see key
Figure 9).
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Joint
Venture Agroforestry Program
(RIRDC/LWRRDC/FWPRDC)
Since 1993, JVAP has led Australia in the development and dissemination
of research and practical information to underpin new sustainable
farming systems incorporating perennial woody vegetation.
The program focuses on commercially driven tree production
systems for addressing land degradation issues. It is developing
new treebased industries for integration into low to medium
rainfall farming systems. The program aims to deliver cost-effective
multi-purpose agroforestry systems to meet commercial and environmental
objectives.
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Opportunity cropping
One option to increase water use by annual cropping systems is to sow
crops opportunistically in both winter and summer, when rainfall and soil
water conditions allow. This is a useful strategy, particularly in the
northern half of the Basin, when summer rainfall is more significant and
soil water storage generally greater (Figures 9, 10).
In the northern part of the Basin, soils with high water-holding capacity
coincide with sufficient summer rain to allow cropping at almost any time
of the year. The modelled volume of drainage from a catchment under current
management was nearly six times that of the native vegetation. Opportunity
cropping yields a leakage volume less than twice that of native vegetation
(Figure 11). However, on soils formed from sedimentary rocks, the difference
between current and best practice is smaller, and both leak considerably
more than the native system.
Figure 11. Modelled leakage under current practice, best practice
and the native vegetation in a catchment in northern NSW.
Source: Ringrose-Voase and Cresswell (2000)
The greatest obstacle to controlling leakage in annual cropping systems
is season-to-season variability in rainfall. Average leakage may be 50
mm/y, but developing farming systems that use an extra 50 mm/y would not
solve the problem. The wetter-than-average years contribute most to drainage
and any sustainable system must have the capacity to deal with such years.
This can only be achieved using perennials.
Annual crops can be made to behave in a more perennial fashion using
phase farming or companion
farming, combining and alternating perennials with annual crops.
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Phase farming
In phase farming, a deep-rooted perennial like lucerne can create a dry
soil buffer of 200 mm or more. This means that it can prevent leakage
most years, and also protect subsequent crops in a rotation. The introduction
of a perennial deep-rooted pasture phase that can dry the soil to 3 m
depth into a cropping rotation (three years pasture followed by three
years wheat) across the 575 mm isohyet, drops leakage by 70% or more (Figure
10).
A key element of farming system design that controls leakage is the ability
to cope with rainfall variability. For instance, long-term simulation
of continuous cropping in central NSW, with 614 mm annual rainfall, produced
an average leakage of 107 mm. In 31% of years, the leakage was less than
50 mm, so the cropping phase could occur for at least four years after
lucerne. However, in 17% of years, the annual drainage was greater than
200 mm. Such a year, coinciding with a depleted buffer, would lead to
unacceptably high leakage (Figure 12).
Figure 12. The modelled probability of getting different amounts
of leakage under continuous cropping in central NSW.
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Companion farming
Companion farming is an emerging concept in which annual cereals are
oversown into a perennial pasture system, ideally one that exhibits a
strong degree of winter and spring dormancy. The perennial pastures may
be native grasslands, like those being trialed by innovative farmers in
northern NSW, or deep-rooted legumes such as lucerne or other novel species.
Oversowing annuals into winter dormant perennial pastures may be a way
of getting around the issue of yearto- year variability in leakage and
the technical difficulty of changing phase.
These systems have been explored in calibrated simulation models (see
Figures 9, 10) and appear to be potentially more effective than phase
farming in controlling leakage, with at least the same grain-yield production
possibilities. However, there may be a trade-off in production through
competition for water and problems with obtaining a clean harvest.
This option could be implemented over the short term (three to five years),
with well-targeted on-farm research and development.
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New agricultural plants
Our current crop and forage species have been bred and/or selected
for yield and desirable agronomic characters. Little or no attention
has been given to their ability to use water and nitrogen and restrict
dryland salinisation.
The immediate opportunities lie in longer season cultivars and species.
Good prospects exist to develop winter wheat and canola varieties that
can be sown as early as February, if rainfall conditions allow, and
grazed in May. They then regrow to produce a grain yield over the normal
spring–early summer period.
Longer term, opportunities lie in the use of both improvements in conventional
plants and developments in biotechnology to develop new plants with
more extensive root systems, greater perenniality, and different degrees
of winter and summer activity. Other traits such as enhanced early vigour,
waterlogging tolerance and disease resistance would also improve their
use of water.
It may be possible to add 'resurrection genes' to annual crops, giving
them the ability to re-sprout after harvest in the event of summer rain.
At the extreme, it might even be possible to produce perennial grain
crops, although it is highly likely that there will be a trade-off between
productivity and persistence. This research frontier has been examined
as part of a new research and development program entitled 'Redesigning
Agriculture for Australian Landscapes' (see below). Some results can
be expected in the next five years, but most of the developments mentioned
above will require 5 to 25 years of focused research.
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Redesigning
Agriculture for Australian Landscapes
The Redesigning Agriculture for Australian Landscapes (RAAL)
Research and Development Program is a joint initiative of the
Land and Water Resources Research and Development Corporation
and CSIRO. The program is researching how agricultural systems
in Australia can be redesigned to address a range of sustainability
issues. It has four objectives:
- To understand, by comparison, the key biophysical processes
affecting leakage of water and nutrients in cropping, grazing
and natural systems.
- To benchmark criteria for redesigning agricultural systems
in Australian landscapes.
- To develop a toolbox of redesign options to modify current,
or develop new, agricultural systems for Australian landscapes.
- To facilitate implementation of redesign options in priority
Australian landscapes by exploring the socio-economic, institutional,
policy, marketing and technological requirements and implications
of each option.
This design approach has potential to be applied through:
- selection and plant breeding — including molecular
genetics — for our commercial crops, pastures and native
plants to manipulate their phenology, canopy development,
rooting function, distribution and temperature response.
- rotating and mixing, in space and time, innovative configurations
of plants including: annual and perennial crops, pastures,
forest and horticultural trees, native plants and bush foods,
in alleys, blocks, windbreaks and clusters, over rotations
of months or years.
Recognising the diverse skills and inputs necessary to achieve
its mission and objectives, the RAAL Program will actively seek
opportunities to collaborate, focusing on:
- integrating RAAL with a range of other redesign initiatives,
and
- incorporating RAAL outputs into other research and development
initiatives.
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Organic farming
Organic farming is increasing in importance due to rapidly growing
market preference. Organic farming uses crop rotations and diversity
to replace agrochemicals, but this does not necessarily mean a shift
to greater use of perennial plants. A similar reliance on annual species
will expose organic farming to the same risk of leakage as conventional
agriculture. Research to give greater emphasis to deep-rooted perennials
in phase planting or as companion plants is attractive because organic
farmers are well disposed towards and skilled in the complexities
of crop/pasture/tree management.
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