Agriculture Reference
In-Depth Information
early in the cropping sequence after compost application (Eldridge et al.
2014
). The
field trial results also showed some soil carbon sequestration benefits from the com-
post treatments relative to the farmer practice for the Sydney basin, being 38.5 %
higher for the third crop (Chan et al.
2008
). However, the benefits of compost in
this regard, could be extended with the adoption of a minimum tillage approach, as
rotary hoe tillage within the CROA experiment was relatively intensive.
7.3.2.3
Nutrient Cycling and the Environment
The experimental data from the CROA field trial also provides some valuable in-
sights into the sustainability of both the current farmer practice and the other trial
treatments in terms of the nutrient cycling for the important plant macro-nutrients
NPK and associated environmental risk. A partial mass balance was determined for
the phosphorus nutrient for each treatment in the experiment by Chan et al. (
2010
)
and this is presented in Table
7.5
. It is apparent in Table
7.5
that the farmer practice,
compost and mixed treatments as farming systems, are all loading the soil up with P
in excess to crop requirements, with only 6, 9, and 9 % respectively being removed
from each treatment in harvested crop produce. None of these systems are sustain-
able in the long term without adjustment, which in part reflects the problem of ap-
plying organic amendments at N fertilizer rates when they have N:P content ratios
(see Table
7.1
) that are much lower than the crop uptake N:P ratio. As such P can
accumulate in the soil over time, eventually posing a risk to water quality and the
environment. In some situations it might, therefore, be more appropriate to use crop
P requirements and soil available P levels as the criteria for determining compost
application rates.
An assessment of the relative environmental risk posed by the farmer practice
and compost treatments was done by Chan et al. (
2010
) at the end of the first five
vegetable crops by a simulated rainfall study and analyses of soil P and runoff wa-
ter samples. It was found that the compost and mixed compost treatment soils had
significantly lower levels of available P (Colwell and CaCl
2
) and total P than the
Table 7.5
Phosphorus inputs (kg ha
−1
) from inorganic fertilizer, poultry litter, and compost and
removal of P (kg ha
−1
) by the harvesting of vegetable crops for the different treatments for the
first 5 vegetable crops in the field trial. Numbers in brackets are the removal of P by harvesting
expressed as a % of total P inputs. (Adapted from Chan et al.
2010
)
Treatment
Inorganic
fertilizer
Poultry
litter
Compost
Total inputs Total removal
by crops
Partial
balance
kg ha
−1
Farmers practice
—low P
151.9
493.4
0.0
645.3
38.4 (6 %)
607
Compost
(125 t ha
−1
)—low P
0.0
0.0
487.5
487.5
43.4 (9 %)
441
Mixed (62.5 t ha
−1
)
—low P
151.9
0.0
243.8
395.7
36.3 (9 %)
359
Nil input control
0.0
0.0
0.0
0.0
11.9
− 11.9
