Agriculture Reference
In-Depth Information
40
Compost
Mixed
Farmer practice
Nil control
30
Compost
application 1
Compost
application 2
20
10
0
0
2
4
6
8
10
Crop number
Fig. 7.10
The mean proportion of the soil as water stable aggregates > 2 mm for each treatment
over the cropping sequence at the CROA vegetable-compost field trial
treatments was degraded with less than 25 % of the soil as water stable aggregates
> 0.25 mm and less than 2 % of the soil as water stable aggregates > 2 mm. This re-
sult largely reflects the influence of tillage on soil structure. The tillage in this study
was done by rotary hoe which is a fairly aggressive tillage implement and is the
standard practice for vegetable production in the Sydney basin. The results illustrate
very well how the longevity of the benefits of the compost application to soil struc-
ture can be undermined by aggressive tillage which accelerates the breakdown of
organic C and also physically pulverises the soil (Chan et al.
2007a
,
2011a
). It thus
seems from these results that a minimum tillage regime may help extend the longev-
ity of the benefits to soil quality that come from compost application.
Another soil physical property that is important to crop growth is soil strength
or resistance to penetration, as it affects the ease with which roots can grow and
explore the soil for nutrients and water. This property was measured to a depth of
45 cm in the experiment plots after the harvest of capsicum using a penetrometer
(Rimik
®
) as described in Chan et al. (
2006
). The mean penetration resistance for
each treatment in the experiment presented in Fig.
7.11
where the effect of the com-
post on soil strength is very apparent down the whole 45 cm profile for both the full
compost (125 dry t ha
−1
) and the mixed (62.5 dry t ha
−1
) treatments. The compost
applications reduced the penetration resistance of the soil, which has implications
for effective root growth and crop access to nutrients and moisture in the soil. It is
