NCEA Level 2 Agricultural and Horticultural Science (90452) 2009 — page 1 of 5
Assessment Schedule – 2009
Agricultural and Horticultural Science: Describe how techniques used to
modify soil water content optimise primary production (90452)
Evidence Statement
Q
Achievement
Achievement with Merit
Describes how TWO soil
properties are changed by
drainage.
Example:
Drainage removes excess
water in pore spaces,
increasing the oxygen
content of the soil.
Removal of excess water
allows surface heat to move
down through soil instead of
evaporating soil water.
Increased biological activity
resulting from improved
aeration and higher soil
temperature.
Explains how changed soil
properties increase crop
yield.
Example:
Increased oxygen in root
zone allows for healthy
roots, and for functions such
as respiration for energy
release, and nutrient uptake
for incorporation into plant
tissues. This increases
growth and yield.
Tile / pipe drainage would
be used to remove excess
(gravitational) water,
throughout the paddock.
These tile / pipe drains
would link into main lines
that lead and drain into the
surface drains at the edge of
the paddock. The surface
drains must allow for the tile
/ pipe drains to drain to a
lower level.
Surface drains, while
relatively cheap to develop
and low in maintenance,
have limited effect. A welldesigned drainage system
involving surface and subsurface techniques is
necessary because the land
is flat and peaty; water will
not move readily to the
surface drains. The
exception will be on land
adjacent to the drains.
Achievement with
Excellence
ONE
(a)
(b)
Warm soil temperatures
encourage cell processes
such as photosynthesis and
breakdown of organic matter
to release nutrients by soil
organisms – both necessary
for new growth and yield.
By removing excess water
(waterlogging) from the
growing zone by tile / pipe
drainage, soil moisture
should be below field
capacity, allowing for free
movement of harvesting
staff, machinery, and trucks.
In doing so, regular
harvesting can occur,
enabling market demand to
be satisfied.
Despite the higher cost of
installation and difficulties
with maintenance when
compared with surface
drains, the key requirement
is to remove excess water
at the time of highest yearly
rainfall. Tiles / pipes work
from below rather than
relying on water moving
laterally with a crop
impeding its movement.
With tiles / pipes, it could be
expected that drainage is
more uniform over the
paddock. There will be no
ponding, as could be
expected from surface
drains on flat land. As a
result, soil aeration and
improved soil temperature
favour root activity, such as
nutrient uptake and cell
respiration. Collectively,
plant activity and growth
are favoured by drainage,
thus increasing crop yield.
Additionally, there are fewer
slugs, etc. favoured by wet
conditions, less soil splash
NCEA Level 2 Agricultural and Horticultural Science (90452) 2009 — page 2 of 5
causing crop
contamination, and better
traction by machinery in
paddocks. This results in
the ability to harvest high
quality crops on request.
In isolation, surface drains
would have minimal effect
on water content in the
centre of paddocks, while
tile / pipe drainage must
have an outlet at a lower
level in order to work
efficiently.
One grade only for the whole question.
Evidence can be provided in answers to either (a) or (b).
Describes TWO soil properties
changed by drainage.
A
Explains, by linking TWO
ideas, TWO ways in which crop
production is enhanced by
drainage.
Explains how the combination
of drainage techniques best
meets market requirements for
crops produced on the property
described.
M
E
NCEA Level 2 Agricultural and Horticultural Science (90452) 2009 — page 3 of 5
Q
Achievement with
Excellence
Achievement
Achievement with Merit
Describes how a soil’s
texture affects water
retention.
Example:
Soil texture, by virtue of
differing proportions of sand,
silt, and clay, has different
ratios of macropores to
micropores. Micropores aid
water retention, macropores
aid drainage.
Explains how trickle
irrigation provides an
efficient supply of water for
grape production.
Example:
Trickle irrigation has
droppers situated directly
above or alongside the
plant, so that only the plant
and its immediate root zone
are wet.
Soil texture affects aeration,
which encourages the
breakdown (oxidation) of
organic matter content,
reducing the soil’s ability to
hold water. Some organic
matter helps water retention.
Trickle irrigation is a low
pressure system with no
spray formation, thus
avoiding water loss via wind
movement.
Descriptions include:
Water budgets – obtaining
relevant climatic data for the
area. Data on rainfall and
evapotranspiration (ET) are
used to calculate when the
stress point (half available
water) is approaching, and
therefore when irrigation is
necessary.
Tensiometers – inserted into
ground to root depth.
Suction, caused by water
movement from tensiometer,
creates a reading on a dial.
Irrigation is required when a
predetermined value is
reached.
Comparisons of accuracy:
Water budgets vary in
accuracy, as they are
dependent on obtaining
accurate evapotranspiration
(ET) and rainfall data. While
rainfall data can be
accurate, the ET data are
often approximations, as
meteorological station data
taken 20 km away may not
apply to a given property.
Daily calculations are
tedious and may not be
made.
Tensiometers are more
accurate, as they measure
moisture levels in the actual
soil. Provided that the
ceramic tip is functioning
properly, there is little that
can go wrong, and the data
is easy to interpret.
TWO
(a)
(b)
Explanation of higher
quality seed:
Tensiometers are specific
to the soil in which soil
water is being measured.
Given that this is a high
value crop with a stipulated
requirement for large seed,
irrigation at flowering and
seed-filling is vital to seed
size – a major determinant
of quality. Substandard
crops – those with small
seed size – will not be
accepted by the niche
market.
One grade only for the whole question.
Evidence can be provided in answers to either (a) or (b).
Describes how soil or plant
factors affect soil water
retention, and how a water
scheduling technique is used.
Explains how TWO techniques
(trickle irrigation and water
budgets or tensiometers) help
to provide plants with readily
available water.
A
Explains how the use of
tensiometers provides higher
seed quality when irrigating the
crop than using water budgets.
E
M
NCEA Level 2 Agricultural and Horticultural Science (90452) 2009 — page 4 of 5
Q
Achievement
Achievement with Merit
THREE
(a)
Describes how TWO
features of mulching
minimise soil water loss.
Example:
A thick layer of organic
material such as straw or
compost spread over the
soil surface kills off existing
vegetation, resulting in no
soil water loss due to
transpiration by plants.
Mulch stops evaporation
from the soil surface
resulting in minimal water
loss.
The layer of organic
material will decompose into
organic matter whose
“sponge” effect helps retain
soil moisture. Plant process
of photosynthesis is not
limited by water availability
to roots.
Explains how mulching
helps crop yields.
Example:
Mulching layer kills off
existing vegetation by
eliminating light, resulting in
no soil water loss due to
transpiration by plants.
Removing unwanted plant
material reduces
competition for nutrients,
light, and water without the
need for mechanical
methods of weed control.
With no soil disturbance,
evaporation losses are
minimal, and so all
ingredients for
photosynthesis are
maximised, thereby
increasing crop yields.
Mulching insulates the soil
from extremes of
temperature, and in doing
so, plant processes proceed
at a faster rate, resulting in
higher yields.
Achievement with
Excellence
NCEA Level 2 Agricultural and Horticultural Science (90452) 2009 — page 5 of 5
THREE
(b)
Description outlines what is
minimal tillage – how the
reduced number of
machinery operations
results in less soil
disturbance and exposure to
drying conditions, eg wind
and sun.
“Minimum tillage”
Explanation outlines how
reduced exposure to drying
conditions results in less air
movement through the
sandy soil, and better soil
moisture retention.
Alternatively, the low organic
matter content of sandy soils
is maintained by reduced
soil disturbance, and aids
the soil’s moisture-holding
ability.
Comparison of techniques:
The difference in impact of
the techniques on crop yield
is not clear-cut, and it could
be claimed that there is no
significant difference in crop
yield. Essentially, any
difference in crop yield will
result from differences in
germination rates due to
moisture differences at the
time of seed sowing.
Because of the reduced soil
disturbance, soil moisture
levels under “minimum
cultivation” should be higher,
thereby aiding reliable
germination, producing
productive plants. Once
plants are established, the
impact of cultivation
technique is minimal, with
soil moisture being largely
determined by climatic
conditions on dryland
properties. Some residual
effects of higher organic
matter could be enhanced
soil moisture and possibly
fungal diseases, reducing
yields in seasons with high
rainfall.
Justification for use is mainly
on savings on time and fuel
rather than soil moisture
levels. However, on sandy
soils there is the potential for
crop yield to be higher.
One grade only for the whole question.
Evidence can be provided in answers to either (a) or (b).
Describes how use of mulching
or “minimum tillage” helps
maintain soil water levels.
Explains TWO aspects of how
mulching or “minimum tillage”
assists plant production by
modifying / utilising soil water.
Compares the effect of the
techniques on crop yields
though their influence on soil
moisture on dryland properties.
M
E
A
Judgement Statement
Achievement
Achievement with Merit
Achievement with Excellence
2A
2M
2E