Biological farming - Soil Essentials: Managing Your Farm's Primary Asset - page 82

(h) Organic additives
There are a large range of specialist organic additives available on the market, most
of which claim to improve soil, plant and animal health significantly. The point to
remember before using these products is to get the soil basics, such as soil nutrient
balance and soil physical characteristics, right first. As many of these products can
be very expensive per hectare treated, it would be wise to try a small trial area to
assess any economic benefit before treating large areas. Lifting soil health and
productivity from a relatively low level as in a damaged soil should be done in
stages, and generally the organic additives are best used later in the improvement
sequence for best results. Another important point is that many of these products
are based on living organisms, and, if spread in the field when conditions are not
suitable, such as hot dry weather, the organisms may not survive at all, or at best be
severely depleted in numbers and not give the benefit hoped for. Any label
instructions should be followed closely for best results.
(i) Weed control
In organic farming, weed control is done by crop or pasture management to reduce
weeds that would affect the following crop, cultivation rather than chemical
control, and techniques such as f lame weeding. In horticultural cropping,
cultivation in conjunction with hand weeding is often used together with
mulching. Newer techniques becoming available are cultures of soil organisms that
can target specific species such as grasses and not damage the crop being grown.
Again, an organic farmer will manage soil according to what is growing on the soil,
which may significantly inf luence the need for weed control for future crops.
(j) Bioextraction of heavy metal contamination
Over time, previous land use techniques have left a legacy of soil and water
contamination by herbicides, pesticides (including the very stable organo-chlorides
such as DDT) and heavy metals such as arsenic, cadmium, lead and mercury.
There are many examples where large areas of land, such as in Iowa and California
in the USA, are severely damaged to the point that it is questionable whether
farming should continue on such land. It should be remembered that if the soil is
poisoned, the crops and livestock growing on that soil can be poisoned. If they are
then used for human food, they can poison us as well, as we are at the top of the
food chain.
Some chemicals can be taken up in significant quantities by specific plants,
and if these plants are grown as a crop and harvested, soil levels of the chemical
can be reduced. If the contaminated crop is then processed, the chemical(s) can
then be recovered for use, or responsible disposal elsewhere.