Biological farming - Soil Essentials: Managing Your Farm's Primary Asset - page 80

The concepts of biological farming
(a) Soil fertility
Biological farmers will maintain or improve soil fertility using systems developed
by observing how this happens naturally without human intervention. These
principles are then used to farm the soil to produce the crops and animals required.
A lot of their success is based on managing the microbial life in the soil, using
crop rotations to best advantage, and managing soil water through building high
humus levels in the soil.
(b) Soil nutrients
Major soil nutrients such as nitrogen, phosphorus, potassium and calcium are
supplied from inputs such as animal manure, nitrogen from legumes, composted
plant and/or animal products, green manure cropping, fish meal and seaweed
products, and crushed rock minerals. Minor nutrients and trace elements are
supplied by mixtures of crushed minerals, wood ash and so on, and releasing
inorganic nutrients already in the soil using biological additives.
One very important soil nutrient is humus, and every effort is made to keep
humus content in the soil as high as possible. This is critical in maintaining soil
microbiology, and soil structure. Organic farmers will also do their best to recycle
soil nutrients, and, in a closed system, all products such as grain, meat, fibre and
the like, which is removed from an area, will eventually end up back on this area
for use by future crops. Humus has the ability to hold soil water and make soil
nutrients available to plants that would otherwise be locked up and unavailable.
(c) Crop rotations
Often a biological farmer will closely observe the soil, and based on these
observations will let the soil tell them when a change of crop is needed. This may
be based on current crop yield, plant species present such as indicator plants and
weeds, soil physical condition such as crusting or compaction, and soil biological
health. A decision will be made on the picture formed from all observations, and
not on one or two inputs only.
In terms of horticultural production (such as vegetables) the tried and proven
crop rotations developed over centuries are used. A very basic rotation is as
follows: manure the soil, heavy feeding crops (greens or leaf crops), then root
crops, then lime the soil and follow with legumes, then back to leaf crops. The
main thing is to balance plant nutrient needs, and not grow plants from the same
family more than once in the full rotation. The exact rotation use will vary with
marketing needs and climatic factors. For example, in cold regions, winter crops
are not particularly successful, whereas in the subtropics, crops can be grown all
year round.