Agriculture Reference
In-Depth Information
systems sometimes have higher pH levels in mildly acidic soils than their conventional counter-
parts (Alvarez
et
al
. 1993, Reganold
et
al
. 1993, Drinkwater
et
al
. 1995, Werner 1997, Clark
et
al
.
1998). During a long-term organic farming study in the Great Plains in Northern Colorado,
Daniel
et
al
. (2002) found that the pH levels in the alkaline soil decreased significantly over time
with organic production. Results from a long-term Swiss trial comparing biodynamic, organic
and conventional farming systems, the DOK (bioDynamic-Organic-Konventional) trial, dem-
onstrate that the utilisation of composted manure, common in organic systems, has a positive
effect on the content of organic matter and helps to avoid soil acidification (Fließbach
et
al
.
2001).
Biological actiity
High biological activity within the soil promotes metabolism between soil and plants and is an
essential part of sustainable plant production and fertiliser management. The role of soil
organisms is central to soil processes and fertility since they render available the elements in
plant residues and organic debris entering the soil (Alföldi
et
al
. 2002).
Earthworms and mesofauna
Earthworms have many positive direct and indirect effects on soil quality, both in terms of
their effects on soil physical properties and nutrient cycling. Furthermore, they are important
in soil organic matter turnover (Shepherd
et
al
. 2003). As a key species of soil mesofauna, they
are an appropriate indicator of soil biological activities as a result of their sensitivity to any
kind of soil disturbance (Stolze
et
al
. 2000). In a synthesis of relevant scientific results, Pfiffner
and Mäder (1997) compared organic and conventional farming systems and concluded that in
organically farmed soils, a significantly higher biomass and abundance of earthworms
occurred as well as a considerably higher diversity of earthworm species. These results were
also reported by Siegrist
et
al
. (1998) during a long-term field trial and by others (Gerhardt
1997, Whalen
et
al
. 1998). A possible reason for the abundance of earthworms in organic
farming could be that organic production depends more on a high, sustained supply of organic
substance from plant residues and manure than conventional farming, which can rely at least
partly on the mineral supply of nutrients. Organic rotations and particularly the inclusion of
grass leys, preferably of several years (>2 years), into farming systems tend to favour earth-
worms because of the beneficial effects of organic matter additions and leys (Rhône-Poulenc
1997, Neale 1998, Scullion
et
al
. 2002). However, organic farming systems rely more on
mechanical weed control and in certain crops, on intensive soil tillage as the use of synthetic
herbicides is prohibited. This can have negative effects on other key species of soil mesofauna
such as Collembola insects (springtails) (Krogh 1994).
Soil microorganisms
The soil microbial biomass serves as a labile source and an immediate sink of carbon, nitrogen,
phosphorus (P) and sulfur (S) in soils and performs critical functions such as nutrient trans-
formation and pesticide degradation. Additionally, microorganisms form symbiotic associa-
tions with roots, control plant pathogens and participate in soil formation (Shepherd
et
al
.
2003). In order to characterise soil microbial activity, parameters like total microbial biomass,
diverse enzymatic parameters, carbon turnover and mycorrhization (mycorrhizal soil fungi
build up symbioses between fungus and plant) are used. Generally, pesticides affect the popu-
lation of microorganisms and fungicides tend to inhibit or kill soil fungi, including mycor-
rhizae (Johnson and Pf leger 1992, Scullion
et
al
. 1998) which are particularly important in
organic systems. At the same time, however, the evidence for increased microbiological activity
under organic farming is mixed. Stolze
et
al
. (2000) reviewed European research results and
