Agriculture Reference
In-Depth Information
80
Compost
application 2
Compost
application 1
Compost
Mixed
Farmer practice
Nil control
70
60
50
40
30
20
10
0
0
2
4
6
8
10
Crop number
Fig. 7.9
The mean proportion of the soil as water stable aggregates > 0.25 mm for each treatment
over the cropping sequence at the CROA vegetable-compost field trial
7.3.2.1
Physical Soil Quality
Soil structural stability is important for maintaining pore spaces in the soil to help
with soil drainage, aeration and crop root growth. The application of compost (and
its associated organic matter) at a high rate was found to greatly improve the soil
physical structure in the compost treatments of the field trial, resulting in a signifi-
cantly (
p
< 0.05) higher proportion of the soil as water stable aggregates which was
still evident in the third crop following the first application of compost (Chan et al.
2008
). The second application of compost similarly improved the soil structure in
the compost treatment soils relative to the farmer practice treatment soils (Figs.
7.9
and
7.10
) where the compost treatment had more than 50 % of its mass present as
water stable aggregates > 0.25 mm. Kremer and Hezel (
2013
) in another field trial
in Missouri also found that organic inputs including composted vegetative residues
had similar benefits for soil structural stability, increasing soil water stable aggre-
gates by up to 72 % compared to conventional farming systems.
However, the benefit of investigating soil structural stability over successive
crops can be seen in Figs.
7.9
and
7.10
where it is apparent that the structural stabil-
ity of the soil is gradually being degraded over time across all treatments including
the compost treatment. By the tenth crop there was little difference in the structural
stability of the soils across the treatments, and the structure of the soil across all
