Implications of Soil Biodiversity for Sustainable Organic Matter Management - Sustainable Management of Soil Organic Matter - page 356

diversity of species is enhancing soil functionality. Van der Heijden et al .
(1998) showed that plant productivity increases with increasing mycorrhiza
richness, and Tilman et al . (1996) showed an increased total resource
utilization (decreasing soil nitrate load) with increasing plant diversity. In
conclusion, both papers show that species provide functions and that
species diversity affects resource utilization in a system.
It was the aim of our investigations to evaluate soil quality in organic
farming systems. A major below-ground process is the decomposition
of organic residues which may be affected by farming systems. Combining
data from holistic measurements with community-level analyses, we
wanted to test the hypothesis that systems with a high diversity make better
use of the available resources.

The 'DOK' Field Experiment

The 'DOK' field experiment (biodynamic, bioorganic, conventional) at
Therwil (Switzerland) is maintained by the Swiss Federal Research Station
for Agroecology and Agriculture, Zurich (FAL, Reckenholz) and the
Research Institute of Organic Agriculture, Frick (FiBL) since 1978 (Mäder
et al ., 1999). It is an experiment with 96 plots in a Latin square. The
systems are managed according to biodynamic (BIODYN), bioorganic
(BIOORG) and conventional (CONFYM) agriculture (Table 5.2.1) and
receive farmyard manure (FYM) at a rate corresponding to 1.4 livestock
units ha −1 .
A conventional system with exclusively mineral fertilization
(CONMIN) and an unfertilized control (NOFERT) are also included. The
systems differ mainly with respect to fertilization and plant protection
strategy, whilst crop rotation (potatoes, winter wheat, red beets, winter
wheat, and 3 years grass-clover ley) and soil tillage were similar.

Table 5.2.1. Main differences of the farming systems in the 'DOK' experiment, yield of winter
wheat (average of the third crop rotation period 1991-1999), and pH and C org values from 1996
(different letters indicate significant differences for manured systems, P< 0.05).

Cropping
system

Mineral
fertilizer

Synthetic
pesticides

Winter wheat yield
(t ha − 1 )

pH
(KCl)

C org
(%) FYM

BIODYN Composted No No

b 4.1 b b 5.92 a b 1.65 a

BIOORG Rotted P, K 1 No

b 4.1 b ba, 5.62 a,b a,b 1.45 a,b

CONFYM Stacked Yes Yes

b 4.6 a

5.40 bc b 1.43 ab

b 4.8 a b 5.01 c

b 1.41 ab

CONMIN No Yes Yes

NOFERT No No No

b 3.0 c b 5.20 c b 1.31 b

1 Rock phosphate, K 2 SO 4 , when deficient.