Agriculture Reference
In-Depth Information
•
& Alms, 1999)
injection of air through various distribution channels including a hollow propeller shaft
recirculated water which is directed through a vortex nozzle held above a tank (Ingham
•
(www.soilsoup.com), venturi nozzles (www.composttea.com) or fi ne bubble diffusion
mats (www.growingsolutions.com)
suspension of compost in stirred, recirculated or aerated liquid (usually water) in a
•
fermentation vessel (Diver, 2001; www.symbio.co.uk/library/fi les/Xtractor%20bro-
chure%202%20x%20A3. pdf).
NCT has generally been made by mixing one volume of compost with between four
to ten volumes of water in an open container. The mixture is stirred as it is made up, then
it is left for at least 3 days at 15-20
o
C with minimal or no stirring (Brinton
et al
., 1996;
Weltzein, 1991). Compost teas can be made in quantities ranging from a few litres to
several thousand litres in a single batch depending on the size of the fermentation vessel.
Nutrients are often added to compost tea at the start of the production process. Recent
work has suggested that the addition of such fermentation nutrients can result in prolifera-
tion of human pathogens including
Escherichia coli
and
Salmonella enteritidis
, therefore
further work is urgently required to determine how to optimize the production process
without putting the manufacturer or user at risk (Ingram & Millner, 2007).
5.4
History of the use of composts and compost
extracts in crop production
Organic amendments, including composts and liquid preparations made from them, have
been applied for centuries for the purpose of crop nutrition and to improve soil quality, but
their use has declined since the advent of agrochemicals (van Bruggen, 1995). Interest has
been maintained through the organic sector, and in recent years the more general pressure
to reduce reliance on pesticides has created a renewed interest in organic amendments
relating to their potential for improving soil health and preventing or controlling pests
and diseases.
Some of the earliest research on the benefi ts of compost was carried out by Sir Albert
Howard in India during the early decades of the twentieth century. Howard, a botanist and
mycologist, pioneered an integrated approach to agricultural research and by observing
local farmers and carrying out basic research he became convinced that the benefi ts of
improved plant varieties could only be fully realized if the soil was also improved. The
use of 'manufactured humus' (compost) was seen to be essential in preventing disease
in plants (and animals) not just in the tropics, but around the world. In 1943 Howard
published his hugely infl uential topic 'An Agricultural Testament' (Howard, 1943) and
his ideas have formed the principles of the international Organic Movement which forbid
the use of artifi cial fertilizers (and other synthetic chemical products) and encourage the
use of composting.
Sprays based on compost extracts have been used for hundreds of years; there is evi-
dence that the Romans used compost teas and the ancient Egyptians used preparations
based on compost or manure extracts as long as 4000 years ago (Koepf, 1992). Interest in
compost extracts and teas waned when pesticides became available in the mid-twentieth
