Geoscience Reference
In-Depth Information
vegetables, because comparisons of whole systems might not compare like with like. To avoid environmental
influences, it is also important to use side-by-side farms. Data from a study by Reganold et al. (1993) are given in
Table 19.11
where only statistically significant differences are shown.
Biodynamic farms have better soil quality than neighbouring conventional farms. This is shown in larger SOM contents,
a more active and varied soil micro-organism population, especially soil mycorrhizae, more earthworms, better soil
structures, lower bulk densities, easier soil penetrability and thicker topsoil.
Differences in chemical properties are less clear-cut; nitrogen is often higher on biodynamic farms, but other nutrients
like calcium, magnesium and potassium may be higher on conventional farms, as may be expected from adding
chemical fertilizers. pH is often lower on biodynamic farms, as the decomposition of organic matter in the soil releases
hydrogen H
+
ions. It is mostly in physical and biological properties that biodynamic and indeed all organic-farm soils
are superior. Many believe that they will withstand climate change better, because plant roots penetrate deeper into
the soil in sustainable systems, and can therefore cope better with drought. More active mycorrhizal fungi mean that
nutrients, especially phosphorus, are solubilized more efficiently in times of stress.
Farming system
Type
Conventional
'High input' agriculture or 'chemical farming'
Alternative
'Conservation' or 'low input' agriculture
Organic agriculture
Biodynamic agriculture
Soil property
Biodynamic
Conventional
Bulk density (g cm
-3
)
1.07
1.15
Penetration resistance 0-20 cm (MPa)
2.84
3.18
Carbon (%)
4.84
4.27
Respiration (_1 O
2
h
-1
g
-1
)
73.7
55.4
Mineralizable N (mg kg
-1
)
140.0
105.9
Topsoil thickness (m)
0.23
0.21
Cation exchange capacity (cmol kg
-1
)
21.5
19.6
Total N (mg kg
-1
)
4,840.0
4,260.0
Extractable P (mg kg
-1
)
45.7
66.2
Extractable S (mg kg
-1
)
10.5
21.5
pH
6.10
6.29
large numbers of calcium ions. Natural vegetation and
crops are both influenced by calcium and pH.
Calcicole
plants are calcium-demanding and intolerant of
aluminium (sugar beet, barley,
Ceanothus
, arctic-alpine
plants in Britain);
calcifuge
plants need little calcium and
are tolerant of aluminium (potatoes, rye, rhododendron,
ling-heather).
CONSERVATION
Types of soil erosion
Soil erosion is the complex set of processes which remove
soil particles from the surface of soil profiles, and redeposit
