“We
are prone to destroy the beast when it aborts, when it gives midgets, or when
it contracts a disease common to ourselves. Destroying the evidence is
apparently a more common practice than diagnosing it to find the cause of the
abnormalities”. — William Albrecht
Several
years ago, I was visited by a sheep grazier from South Australia who had
converted his property to organic in 1963. I asked him what he did about worms
in his sheep. “I used lead,” he said. “For the first three, or four years after
conversion, I shot any sheep with worms and I slowly bred the susceptibility
out of them”.
This
does not mean that organically raised sheep never get worms. Parasitic worms in
livestock like fungal disease organisms in the soil, are always present. It is
only when they get out of hand that they are a problem. It is very likely that
a low level of some of them are essential to the livestock’s well-being.26 The causes of worm problems include
stress, genetic susceptibility and malnutrition. One of the main problems of
our recent worm control strategies has been the covering up of genetic
susceptibility. Prior to the widespread adoption of anthelmintics, susceptible
beasts were either culled by the grazier, or Nature. In personal comment on
this, a member of the Tasmanian Department of Primary Industry told me that
parasitic worms were more prevalent in livestock today than they were prior to
the introduction of modern anthelmintics. Since there are no new anthelmintics
on the horizon and there is widespread resistance to most of those in current
use, we have no choice other than to adopt a more organic approach to the
problem.
Apart
from genetic susceptibility, probably the most prevalent cause of parasitic
worm problems is nutritional stress. The pursuit of higher grass yields,
regardless of pasture quality, has led to an overall decline in livestock
health. This has been masked, not cured, by ever increasing veterinary chemical
inputs. I am not arguing here for the elimination of veterinary chemicals, but
against farming strategies that necessitate their overuse.
One
useful piece of research suggested by my friend Dr Mike Walker would be to
question stock agents about the relative health status of a large number of
properties. The pastures of those known to produce consistently healthy
livestock could then be analysed for their balance of grass species, grazing
management and fertility status of the soils.
Many
organic farmers go to some lengths to diversify the pasture species grown
beyond the usual grasses and clovers. The ubiquitous flatweed plantain, for
instance, supplies more protein to stock than clover. When clover is grazed,
the nitrogen fixing root nodules detach and decompose in the soil. The released
bacterial protein is then consumed by the plantain before it is in turn
consumed by the livestock. New Zealand agronomists have developed strains
superior to the wild types.
Other
useful species that generally need to be sown include chicories, yarrow and
sheep’s burnet. Grass, clover and herb mixtures (herbal ley) are readily
available from seed merchants in Europe and North America, but sadly not here
as yet.
We
have already referred to the necessity of balancing the ratios of the major
cations, calcium, magnesium, potassium, and sodium in the soil. Not only does
this result in better crop health, but also better animal health. Where the
soil is unbalanced, the stock’s nutritional requirements can be balanced by the
judicious use of mineral licks, or drenches. Pate Coleby, a Gippsland farmer
has pursued this route with some interesting results. When her mineral drenches
were compared to veterinary chemicals by the Victorian Department of
Agriculture, the results were remarkably similar. One suspects that the
minerals were considerably less expensive than the veterinary chemicals.
Many
organic farmers the author has spoken to emphasise the importance of avoiding
stress to livestock as a prime means of avoiding health problems. For instance,
Alfred Haupt, a Bio Dynamic sheep grazier and cropper in New South Wales, talks
about the different smell of sheep that are frightened. This smell, he says, is
attractive to flies. By minimising loud noises (such as those generated by
motorbikes and noisy dogs) he reduces fly strike problems. Those few that are
struck are treated with a mixture of pyrethrum and garlic. The pyrethrum kills
the maggots and the garlic heals the wound rapidly while at the same time
repelling flies that may strike the wound again.
Bert
Farquhar, a Tasmanian grazier, planted out walnut trees on his properties
Wyambi and Rushy Lagoon. He says that the flies are repelled by the smell of
walnut trees. Bert also emphasised the necessity for reducing stress in livestock,
not just for health reasons, but but for the all important economic ones. His
yards are all set up to allow the stock to be mustered facing into the wind. He
says that when the wind comes from behind, it lifts their coats and they become
fractious and more difficult to handle.
When
lice are a problem, they are readily treated by dusting with diatomaceous
earth. This material is the remnants of the skeletons of microscopic organisms,
called diatoms. The sharp edges of the particles are a potent and effective
insecticide as they damage the breathing tubes of the target organism. On this
account, DE is probably not so good for the lungs of beast or farmer. Where
lice are persistent, the nutritional status of the stock is probably
inadequate.
When
worms become a problem, a mixture of garlic pulp and cider vinegar (50:50) is
an effective vermifuge. We acquired our sheep from a farmer converting to Bio
Dynamic. She had phoned me for an organically acceptable alternative to the
usual worm drenches. Her lambs had to be agisted during a drought and they
became infested with worms. As well as suggesting the garlic/cider vinegar
drench, I also offered to buy some of the lambs. She and her veterinary husband
delivered the lambs about a fortnight later, and I asked the husband for his
opinion regarding the effectiveness of the drench. His comment was that he had
never seen such a dramatic overnight change in his life.
Another
enthusiastic organic convert, Claude Conlan, told me he had to wait several
months following learning about garlic/cider vinegar, before he had the
opportunity to try some on his cattle. Not only was he pleased with the result
of the drench, he said that when he mustered the stock for a follow-up drench
three weeks later, the stock were unusually tractable. When mustering following
a conventional drench in the past, the stock had always been quite irascible,
he said.
Tasmanian
dairy farmer, Ray Mason, applies dilute seawater as a spray to his pastures. In
addition, he provides dilute seawater as well as fresh water for his stock to
drink. He believes that this is largely responsible for the superb health of
his cattle. One unusual side effect of the seawater spray was its remarkable
effect on the blackberry rust. On Ray’s side of the blackberry hedgerows, the
leaves were unaffected, but on his neighbour’s side, the brambles looked as
though they had been sprayed off.
Human Nutrition and Health
There
has been a lot of rubbish written and fad-foods consumed in the name of proper
human nutrition over the years. We have already referred to Albrecht’s
discovery of the apparently better health of humans consuming food growing on
the same land that supports the healthiest livestock. That is, the major
nutrients calcium, magnesium, potassium and sodium need to be in correct
proportion.
Eve
Balfour in her book, Soil and Health, drew similar conclusions. She further
concluded that the best human health was exhibited by populations eating whole
food regardless of whether it was a vegetarian, meat, or fish based diet. Much
of modern nutritional problems stem from diets that are unbalanced and consist
of excessive amounts of fat and processed food. For instance, the human
organism absorbs cadmium more readily when zinc is in short supply. Zinc
accumulates in the bran of the wheat berry, cadmium in the starchy gymnosperm.
The production of white flour entails the removal of the bran carrying the
zinc, leaving the gymnosperm carrying the cadmium. In other words, consuming
white flour is likely to increase your cadmium absorption when compared to
consuming wholemeal flour.
A
persistent claim of one sector of the green movement is that modern synthetic
pesticides in the diet are a major cause of human cancer. There is precious
little scientific evidence for this.27 On the other hand, there is scientific evidence in favour
of other causes; in particular, stress. The persistent and possibly erroneous
claim that pesticide residues in our food are exposing us to an unacceptably
high risk of cancer itself must cause stress. Since we know that stress increases the risk of cancer, perhaps those making
the claim are themselves inadvertently increasing the risk of cancer.
We
are not trying to imply that growing systems have no effect on human nutrition
and health, we are just trying to put it in perspective as part of a larger
picture. Given the conclusions drawn concerning livestock nutrition in the
previous chapter, it seems likely that the method of growing our food does have
an influence on its nutritional qualities and hence its effect on human health.
However, this must be balanced against the fact that these effects are probably
masked by overall bad food consumption habits and arguably poor medical
practises.
One
interesting trend over recent decades is that sperm counts of Western males has
declined considerably. The average American male is functionally sterile. This
does not mean that they are incapable of impregnation, but that many more
attempts are now required for success. Thirty men attending the AGM of the Danish
National Board of Organic Farmers were asked to donate sperm for comparison by
the Danish State Hospital. They all had diets that included at least 50%
organically grown produce. There sperm counts averaged 104million per
millilitre compared to the accepted average of 50-55 million. While the sample
is too small to be definitive, it has led to a proposed three year clinical
trial.28
Conversion to Organic Farming
Pasture
is very easy to convert to organic production methods. Quite small amounts of
pelletised poultry manure, or liquid fish have proved capable of stimulating
the soil biology in a matter of weeks. We have seen the root depth increase
from around 50 mm to 300 mm after twelve months. This allows the grass roots to
reach nutrients they would otherwise be unable to obtain and pulling of the
grass in winter is eliminated. The consequent increase in humus level from
around 1.5-2.5% to 4-5% increases water holding capacity from 12-38 mm to
100-150 mm. This increase naturally improves grass production and extends the
growing season in dry weather. It is important too, to realise that when humus
levels are below 2.5%, the cationic nutrients, calcium, magnesium, potassium
and trace elements, leach. When the humus level is a more acceptable 4-5%,
leaching ceases to be an issue.
The
first indicator that the biological activity is on the upswing is the presence,
in appropriate soil conditions29
of earthworms. There are instances of pasture without earthworms and they
benefit enormously from their introduction. Tasmanian farmer, Bert Farquhar,
doubled his stock carrying capacity when he introduced European earthworms to
his properties Rushy Lagoon and Wyambi. It is pointless to look for earthworms
when the soil is too hot, or too dry. Generally, their activity is at a peak in
mid spring, when soil temperatures are between 10 and 20°C.
Beware
of people selling earthworms. There are two main sorts, pasture worms and
manure worms. The worms propagated by worm farmers are nearly always manure
worms. They are adapted to very high organic matter levels and do not consume
soil. Pasture worms in the typical worm-farm situation die out after a time.
Nearly always, earthworm absence is a symptom of inhospitable soil conditions.
They require the pH to be between 5 and 8 and for there to be adequate organic
matter and moisture. Where they must be introduced, it is best to cut turf from
pasture with earthworms and place pieces, grass side down, at 10 metre
intervals to seed the pasture needing them. The pieces are generally about 100
mm by 150 mm. There are manufacturers of specialised turf cutting machinery in
New Zealand.
A
similar response to organic fertilisers has been noted in pome fruit orchards.
Soil that showed no sign of earthworm activity for decades became liberally
covered with worm casts in the spring following winter application of
pelletised poultry manure. Kiwi fruit orchards in New Zealand responded
similarly to a soil drench of liquid fish.
Many
field crops have also responded well, but the heavy feeding, long season crop,
potatoes has been disappointing. Sap analysis showed that pelletised poultry
manure was supplying adequate levels of nitrogen and potassium, elevated levels
of calcium and trace elements, but very poor mobilisation of phosphorus. This
would seem to indicate that a mixture of pelletised poultry manure and
superphosphate (or rock phosphate) would give better results. A crop receiving
a mixture of 1 tonne per hectare of poultry manure pellets and 300 kg per
hectare 11:12:19 outyielded one receiving 1200 kg per hectare 11:12:19. The
potatoes that received poultry manure pellets were hardly affected by either
blackleg and blight. The potatoes grown on 11:12:19 alone were badly affected.
Inspection
of the soil these various potato crops were growing in showed little sign of
earthworm activity when compared to pasture, pome fruit orchards and a hop
field trial. While potato farmers acknowledge that the best crops are grown
coming out of pasture, very few growers now include a pasture phase in their crop
rotation. It is highly likely that the reduction in earthworms in cropland is
due not only to continual cropping and subsequent excessive tillage, but also
the soil compaction created during winter potato harvest. One simple solution
to the latter problem would be to harvest the potatoes in autumn, when the soil
is still dry and store them in sheds until needed. This would also allow the
sowing of a green manure crop to reduce winter soil erosion which is quite
dramatic when viewed from the air over the sea near river estuaries.
The
increase in calcium uptake as a result of the addition of organic manure to
potato crops is an indication that the potatoes will store better. One of the
most frustrating problems in recent years has been the poor quality of potatoes
grown under a conventional regime.
The
summer of 1992/3 was particularly wet in northern Tasmania and the tops of most
potato crops died off very early from the fungal disease, target spot. Two
crops, both grown on conventional fertiliser, were treated with foliar sprays
of liquid fish in one instance and dilute pig slurry in the other. Both crops
lived a good six weeks longer than the untreated crops and outyielded them by a
good margin. Both the treated and untreated crops received the usual fungicide
program.
We
believe that there is a potential to increase potato yields and quality by a
judicious mixture of organic and artificial fertilisers. This would allow some
land to be returned to pasture, which in turn would enable the humus level and
consequently the fertility of the soil to be built up. The pasture phase would
not necessarily require stocking with animals. A cow grass, or lucerne pasture
could be mowed and the dried, shredded material used as a substitute protein
source in place of pelletised poultry manure.
It
used to be that permanent pasture lasted for centuries. These days, many
farmers consider themselves lucky if “permanent” pasture lasts for a decade.
What has gone wrong? First, the pasture is regularly fed with superphosphate,
keeping the bulk of feeder roots close to the soil surface. This leads to very
shallow roots on the pasture grasses. Since the roots can only exploit what
they can reach, they must subsequently be continuously fed to maintain
production. The shallow roots also lead to a drought-prone condition and the
grazing animals readily pull the grass, roots and all, from the ground. This
leads to gaps in the sward that are repopulated by weeds, such as thistles.
A
further problem arises if urea is used to boost production. Any nitrogen in
excess of the crop’s needs is utilised by the soil micro-organisms. In order to
balance their diet, they consume the organic matter in the soil. This in turn
leads to reduced humus levels and fertility, necessitating increasing amounts
of urea to maintain the same grass yield.
Organically
managed pasture in good heart has deep roots and high organic matter levels.
Production is maintained longer in dry conditions and it resists invasion by
undesirable weeds. Water falling on it is more quickly absorbed and more is
retained. Fertiliser amendments, including lime, are needed only infrequently.
Converting
existing pasture to a more organic system is relatively easy. First, you need a
soil test (or tests) to establish the balance of calcium, magnesium, potassium
and sodium. Nearly always, the required balance can be achieved with dolomite,
or ordinary limestone. If potassium is deficient, amendment should wait the
outcome of a year, or two of conversion, as potassium levels can rise dramatically
in response to organic fertilisers. Probably the cheapest and simplest
amendment to use at this stage is fish emulsion. Very little (10-20 l/ha) is
required as you are feeding the soil microorganisms, not the grass. It is applied with a boom spray, or better a field
jet. On Flinders Island, the graziers call this a rooster tail because of the
shape of the spray. The field jet allows a coarser spray, less prone to wind
effects and doesn’t have the fine filters of a boom spray. If you do use a boom
spray, removing the filters will allow a faster application rate.
An
alternative to fish emulsion is pelletised poultry manure. Only 3-400 kg/ha is
required.
The
first effects of organic manuring observed by most farmers are preferential
grazing of the treated areas and an improvement in stock health. Digging a spit
of soil in treated and untreated areas several weeks after treatment shows
improved root depth, increased clover nodulation and better moisture retention.
After several years of such a regime, you will find it no longer necessary to
apply the fish emulsion, or poultry manure annually. You will have a
self-stoking cycle going.
The
period between amendments will vary considerably, depending on soil-type,
pasture species mix and what is being exported from the farm. Clover acidifies
the soil and promotes leaching of calcium and magnesium. The rate at which this
occurs is a function of the rainfall and proportion of clover in the pasture.
If milk is being exported, this will add to the calcium drain. Wool, on the
other hand, will reduce sulphur quicker. Much animal protein consists largely
of carbon, hydrogen, oxygen and nitrogen, all of which can be supplied from the
atmosphere.
Maintaining
pasture also requires management other than fertiliser inputs. Pasture
production and health are optimised when grass length is maintained between 25
and 150 mm. If this cannot be achieved with stock and fodder conservation, then
mowing paddocks that are long is required. Regular harrowing will also assist
aeration of the top few centimetres of soil and increase the rate of breakdown
of animal manure.
“They
are a savage, wicked brood… all experienced husbandmen… would unanimously agree
to extirpate their whole race as entirely in England they have done the wolves,
though much more innocent and less rapacious than weeds.” — Jethro Tull
Most
farmers have come to rely very heavily on herbicides for weed control. While on
the surface, chemical weed killers appear to provide many benefits, they are
also a two-edged sword. Some farmers have discovered that when soil humus
levels fall to a very low figure, herbicide residues in the soil are
reactivated to the detriment of the crops. Some herbicides are ineffective in
soils with too high organic matter levels. Given the manifold benefits of high
organic matter levels in the soil, it would appear to be a poor farming
strategy to limit them to maintain the effectiveness of herbicide.
In
the winter of 1994, Monsanto wrote to many farmers (including the writer)
offering a “free” cricket hat in return for buying their product and advising
farmers to use a mixture of Ramrod Flowable® and Stomp®
on their onion crops. A few weeks later, a letter arrived apologising for any
inconvenience this advice had caused; it was incorrect. The effect of this
mixture was not stated, but one imagines it was deleterious. Given the volume
of sales literature that crosses my own desk, it is not too hard to imagine
some farmers missing the second message, particularly since the letter was
headed “Roundup® and Your Free
Cricket Hat”, hardly designed to arouse the farmers’ attention to problems
caused by Monsanto’s bad advice.
Invariably,
some plants are resistant, or immune, to any particular herbicide. This has
given some weeds that were previously innocuous a competitive edge,
necessitating the use of yet another herbicide.30 As well, some herbicides, notably glyphosate, appear to
inhibit uptake of trace elements by crops. Above all, the observation I have made
on many farm walks is that organic farmers appear to have less weed problems than their conventional counterparts.
There
are several strategies adopted by organic farmers to control weeds. Probably at
the forefront, is the maintenance of a fertile soil. Many weeds are a response
to less than ideal soil conditions for crops. Dock and wire-weed, for instance,
are a response to compacted soil. Thistles are a response to under, or
overgrazing31 and to a
lesser extent, excess nitrate levels in the soil. Cape weed is a response to
low soil fertility. On my own farm, we had a one acre paddock of vegetables for
a couple of seasons, before returning the paddock to pasture. For the ensuing
four years, you could clearly see where the footpaths between the raised beds
had been by the number of docks in the paths. Gradually, the docks broke the
hard pan and in so doing, reduced their competitive edge and the grass sward is
now nearly uniform.
Victorian
farmer, Frank Chenowyth, farmed conventionally from 1954 to 1984. He was facing
mounting stock health problems and decided to devote the money he normally
spent on super to trace elements. Apart from a dramatic improvement in stock
health, he also noted the proliferation of desirable pasture species at the
expense of weeds without the necessity for resowing.
Tasmanian
dairy farmer, Joe Gretchman, takes a different tack. While most farmers have a
profound hatred for the toxic weed ragwort, Joe is “letting Nature take its
course”. He estimates that slightly less than 5% of the pasture is occupied by
ragwort plants, so the decreased yield caused by their occupying soil that
would otherwise be growing grass is negligible. Joe also pointed out that the
roots of the ragwort go down between one and two metres. They absorb nutrients
that the shallower pasture grasses cannot access and deposit them at the soil
surface when they drop their leaves. Of course it is essential that ragwort
that might end up in hay be removed.
When
Tim Marshall visited Queensland Bio Dynamic grazier and cropper, Alfred Haupt,
he remarked that the thistles looked as if they had been recently sprayed with
herbicide. Alfred explained that he flooded the paddock and left the water
until the clover was almost drowned. The thistles were less resistant to waterlogging
than the clover and expired.
These
examples were given to illustrate the wide variety of attitudes and strategies
adopted by different farmers. In organic farming, weed control is rarely
oriented toward the rather unrealistic goal of total elimination. Many weeds
can be kept to tolerable levels without resort to poisoning, or excessive
cultivation.
Cultivation
remains the primary method of weed control in cropping. It has been pointed out
that cultivation is responsible for much damage to soil structure and
contributes to soil erosion. However, organic farmers defend their preference
for cultivation to herbicides. They point out that organically managed soils
are more tolerant of cultivation since their structure is better than soil
under a conventional regime. As well, their crop rotations are generally more
diverse and almost invariably include a pasture phase which all contribute to
lower weed infestation rates.
Many
organic farmers use alley cropping to minimise soil compaction and increase
yields. This entails the creation of permanent raised beds with the tractor
tyres always in pathways between. The structure of the soil in these raised
beds is never compacted, reducing the need for excess tillage. Weed control
implements are chosen for their ability to minimise soil inversion. There can
be more than two billion weed seeds per hectare in the soil, some 15% of which
are capable of germination. Shallow, non-inverting tillage reduces the number
that germinate. Deep tillage to reduce hard pan is virtually a once off
operation immediately prior to the formation of the permanent raised beds.
Choice
of crop variety can play a role in weed control. Many organic wheat farmers
grow older, long-straw varieties in preference to the more recent short-strawed
varieties. These provide more shading at the soil level and this reduces the
ability of weeds to compete. While the conventional farmer perceives little
virtue in growing straw at the expense of grain, to the organic producer, straw
is a valuable resource as it is a source of organic matter to improve soil
structure. Since many organic wheat farmers also undersow the crop with clover,
this also reduces weed competition as well as providing nitrogen.
Conventional
wheat farmers are no doubt raising their eyebrows at these strategies, since
they also reduce crop yields. It is important to emphasise that the farmer’s
goal should not be yield at the expense of everything else. A grower losing 5
kg of topsoil for each kilo of wheat grown is living off his, or her capital.
No business can expect to survive in this circumstance. It was enlightening to
follow a dialogue between organic and conventional wheat growers at the 1990
organic agriculture conference at Adelaide University. The organic growers
reported little or no problems with fungal diseases, such as take-all and rust.
This was received with some scepticism by the conventional growers. The most
important point here is that organic wheat growers make incomes that are almost
identical to their conventional counterparts.32
While
at the 1990 organic agriculture conference in Adelaide, participants went on
several farm walks. One of the most interesting to me was a Bio Dynamic market
garden, where for the first time I saw a flame weeder. This device has an LPG
gas burner underneath a shroud that reflects the heat onto the soil and
emerging weeds. The weed seedlings are raised to a temperature of around 60°C
and this coagulates the protein in the sap, effectively killing them. The
grower said it cost $40/ha to flame weed compared to $70/ha for herbicide.
German farming implement designer, Bernward Geier, pointed out several aspects
of the machine the farmer was using that could be modified to improve its
efficiency.
New
Zealand vegetable producer, Marinus La Rooj also uses a flame weeder for
pre-emergence weed control. He places a small sheet of glass on the seed bed
immediately after sowing a crop. This accelerates germination under the glass,
so when the crop seeds emerge there he knows it is time to flame weed. On Marinus’
farm, post emergence weed control is with a tickle-weeder. This implement
consists of many flexible stainless-steel tines that vibrate as they are
dragged across the soil. Well-established crops, such as carrots, pumpkins,
lettuce and brassicas push the tines to one side and receive remarkably little
damage. Weed seedlings at the white-wire stage are dragged from the soil to
die.
Another
weeding implement favoured by organic vegetable producers is the brush-hoe.
This resembles a miniature street sweeper, the slowly rotating bristles
penetrating the soil to a depth of about 25 mm. This works on more established
weeds than the tickle, or flame weeders. The leaves are pulverised and left on
the soil surface to act as a mulch, reducing further weed seed germination and
reducing moisture loss.
A
friend establishing a vineyard trialed three approaches to weed control; weed
mat, hay over newspaper and herbicide. The hay and newspaper mulch was by far
the most effective, though also the most labour intensive. The weed mat was
much quicker to apply, but appeared to reduce the water-infiltration rate from
the drippers. Also, many weeds had their roots under the mat and grew outward
under the edges. The herbicide-treated rootlings were the least vigorous.
Mulching
perennial crops by hand is torturous and back-breaking and that is not a recipe
to delight the average farmer. However, there have been a number of implements
developed to shred mulch materials and deposit them alongside the crop. Typical
mulch materials are newspapers, straw and hay bales. Queensland cane growers
have remarked the results obtained by depositing crop trash in situ versus
burning. It has reduced nitrogen leaching, improved weed control, improved
water infiltration rates and moisture retention.
A
novel approach to mulching was taken by the Tasmanian Department of Primary
Industry. They developed a system whereby oats were sown into an onion crop.
The root system of the oats reduced the problem of soil washing in the winter
rain. Often, erosion in heavy rain is sufficient to remove immature onion
plants. In the late winter, or early spring, the crop was sprayed with a
selective herbicide to kill the oats. The dead oats acted as a mulch for the
onion crop, obviating the necessity for continual herbicide sprays that are
usually necessary.
A
more organic approach was that taken by the CSIRO and its use of sub-clover.
Under typical Australian climatic conditions, sub-clover is summer-dormant, so
summer maturing crops planted into a sward do not suffer from competition with
the clover. The clover takes off in the winter months to fix atmospheric
nitrogen and its residue acts as a moisture-conserving and weed-suppressing
mulch in the summer months.
Grazing
to control weeds in perennial crops is an effective way of achieving multiple
land-use. Australian Hop Marketers at Gunns Plains in Tasmania’s north west use
sheep to control weeds for much of the year. The hop vines are only grazed by
sheep when they shoot their young foliage in the spring. This period is only a
few weeks. For most of the year, the hops are either dormant, or too mature to
interest the sheep.
Like
their conventional counterparts, most organic farmers use traditional
cultivation equipment for weed control. Many weed seeds need light in order to
germinate and cultivating in the dark can reduce weed seed germination rates by
98% according to German research.33 Weeds such as fat hen, cleavers and chickweed were severely
checked. Others, such as toadflax and wild chamomile were stopped completely.
Conversely, if you want to stimulate weed seed germination to reduce the number
of seeds, it is best to cultivate in the middle of a bright sunny day.
Unfortunately, weeds that multiply vegetatively, such as couch grass, can
increase through night-time cultivation. This research opens many
possibilities, such as the development of light-proof covers for harrows that
would allow arable work to remain a daylight occupation.
While
hand tools are little used these days by conventional farmers, they have a
place on many organic farms. This is not because organic farmers are Luddites,
but because they are an economical alternative to power tools, large and small.
One such is the GR Wheel Hoe manufactured and marketed by Gundaroo Tiller. The
oscillating stirrup hoe is very efficient and because of its curved bottom and
vertical sides, allows working very close to plants without risk of damage to
roots. It is at least as efficient for weed control as a walk-behind rotary
hoe, much quieter and doesn’t consume any fuel.
Gundaroo
Tiller also market Eliot Coleman’s Gung Hoe. Eliot developed this hand-held hoe
during his thirty or so years of market gardening. He discovered that using the
hoe more like a broom, sweeping the blade through the soil, just under the surface,
was much more efficient than the chopping action of conventional hoes. This is
because chopping uses wrist muscles. The Gung Hoe approach makes more use of
the shoulder muscles, reducing operator fatigue. As well, the Gung Hoe is
angled precisely for optimum efficiency. Conventional hoe blades are at a 65°
angle, the Gung Hoe 70°. The blade is reduced in width to reduce friction and
the shank spot welded to the upper face of the blade for the same reason.
A
weed control system in development is the use of myco-herbicides. These are
plant pathogens, often fungi, and they are applied with regular spray
equipment. Most are highly specific, attacking only particular weeds. It
appears likely that combinations of myco-herbicides will be developed to more
closely imitate conventional broad-spectrum herbicides.
Many
living organisms generate natural toxins that could be developed for use as
herbicides, just as pyrethrins from Chrysanthemum species have been used to
poison insects. Such materials would have an advantage over myco-herbicides in
that they are not living organisms and therefore could not proliferate and
spread in the environment to attack non-target plants. They would also be less
affected by weather conditions that can inhibit the effectiveness living
organisms. One that was developed in the United States had its origins in the
Tasmanian Bluegum (Eucalyptus globulus) but has yet to reach Australia.
Also
in this vein, many plants produce chemicals that inhibit other plants living
nearby. They are called allelo chemicals and it is likely that these are
responsible for many of what organic gardeners call companion planting effects
and scientists call allelopathy. There are two approaches to utilising these
substances. While the production of allelochemicals is very common among wild
plants, this ability appears to have been unintentionally bred out of almost
all our cultivated species. Perhaps there is scope for breeding the ability
back in by cross breeding with the wild ancestors of our crop plants.
Alternatively, allelochemicals could be used to develop a new class of
herbicides. It is interesting to note that allelochemicals have a more potent
effect in soils low in humus and bacterial activity. This could explain why
weed competition is less of a problem to organic farmers.
A
New Zealand company, Waipuna Systems of Aukland, is pioneering the use of steam
weeding. Their steam weeder can be used in any weather and is effective almost
immediately, the results being directly comparable to glyphosate. The New
Zealand Crop and Food Research Centre carried out trials in 1993 that showed
all annual and some perennial weeds were completely killed. Dock and dandelion
took 40 days to recover.34
Other
emerging technologies include electrostatic discharge, laser and microwaves.
These are all similar in their effect to flame weeding with its limitations on
use in established crops. As well, their effectiveness is dependent on factors
such as the duration of exposure; they can be very slow. Perhaps they will
become more widespread as they are further developed.