NCEA Level 2 Agricultural and Horticultural Science (90452) 2008 — page 1 of 5
Assessment Schedule – 2008
Agricultural and Horticultural Science: Describe how techniques used to modify soil
water content optimise primary production (90452)
Evidence Statement
Q
Evidence
Code
Achievement
Factors include:
 Soil texture – the proportion of clay,
sand and silt.
 Soil type – the proportion of
macropores to micropores.
 Soil structure – the ability of
structure to maintain porosity and
drainage.
 The level of organic matter present
in the soil.
 The number of drying winds
influencing evapotranspiration.
 The amount of rainfall received.
A
Describes TWO
factors that affect
the rate of soil
water loss.
A
OR
M
Describes soil
water content
between its stress
point and full
capacity as being
increasingly
available to
plants.
A
Describes how
the selected
technique is used
to measure or
predict when soil
water is close to
its stress point
and when it is at
90% of field
capacity.
Achievement
with Merit
ONE
(a)
(i)

(ii)
(b)
The type of crop and root depth
(crop use).
Describe
Irrigation to 90% of field capacity
means there is a high chance that all
irrigation water will be readily available
to plants (enough to meet plants’
needs).
Explain
 However, if irrigation takes the soil
to field capacity, then any rainfall
following irrigation may push the
soil water content above field
capacity, so water will be lost in the
form of gravitational water. As a
result, the benefits of any rainfall
are lost.

Plants do not have to expend as
much energy to extract soil water,
therefore more energy is available
for plant growth.

Possible context could be leaching.
A tensiometer is buried in the soil.
Suction of water from a tensiometer
into soil creates a pressure that is
measured on a dial.
A neutron probe is inserted into soil at
an appropriate depth. Readings from
the gauge / dial / meter indicate soil
water content in relation to its stress
point and field capacity.
Aquaflex tape is buried in soil at an
angle where soil water can be
measured at different depths. Readings
received by electronic equipment
indicate soil water content in relation to
its stress point and field capacity.
Explains how
water in excess
of field capacity
is lost to plants
and represents
a waste of water
resources
(efficient use).
Achievement
with Excellence
NCEA Level 2 Agricultural and Horticultural Science (90452) 2008 — page 2 of 5
Q
Evidence
Code
Achievement
ONE
(c)
Eg Rank order:
(1) B – neutron probes
(2) C – Aquaflex tape
(3) A – tensiometer.
Explanations could include
Although a tensiometer is buried, its
dial is exposed above ground and
subject to damage by machinery
and irrigation equipment. Many
would be required to monitor the
bean crop’s soil water levels, and
reading tensiometers presents
difficulties when they are located
amongst a leafy crop.
Neutron probes are used to record
and graph soil moisture values.
These graphs, along with
recommendations, are sent to the
grower. Accuracy is high, but there
is a cost factor to consider. Beans
are a high-value crop that is in the
paddock for only about four months;
therefore the cost of a neutron
probe specialist will be justified.
Aquaflex tape is buried in the soil
out of the way of any action that
could damage the tape. It is
normally laid at a depth deeper than
the shallow-rooted bean crop and
therefore could lack some accuracy.
The results are easily read by
growers, while costs per crop are
small given that the cost of the
permanently installed technique is
spread over all crops to be grown in
that paddock.
A
OR
M
OR
E
Evidence toward
A for Q 1 (b)
possible if new
information
describes how a
technique is
used to modify
soil water
content.
Award A if a new
water scheduling
technique not
used in Q 1 (b) is
described.
(d)
How techniques produce the
selected benefit
Reduced loss of fertiliser

The loss of soluble fertiliser
through leaching, due to
excessive irrigation and
additional rainfall occurs on
free-draining soils.

Knowledge of when the soil is
approaching field capacity will
allow for good decision-making
as to when to stop irrigation and
so avoid leaching of fertiliser.
Increased crop yields

Crops require freely available
water at key times, such as
flowering and seed formation.

Knowledge of soil water status
is critical in order that water is
present for photosynthesis and
nutrient uptake at the key
growth periods that affect yield.
M
Achievement with
Merit
Achievement with
Excellence
Evidence toward
M for Q 1 (b)
possible if new
information
explains how a
technique used to
modify soil water
content can
optimise primary
production.
Justifies the order
of techniques by
explaining why a
technique is more
suitable for the
grower to use
compared with
ONE of the other
techniques in terms
of predicting /
measuring field
capacity.
Requires:
 1 valid
comparison
between TWO
techniques, e.g.
damage by
machinery,
cost, accuracy.
Explanation of how
the selected
technique
produces benefits.
Must provide a
linkage between
knowledge of soil
water status and
leaching OR
humidity / moisture
reduction OR plant
processes.
NCEA Level 2 Agricultural and Horticultural Science (90452) 2008 — page 3 of 5
Q
Evidence
Code
Achievement
“Hump and hollow” is used on dairy
farms in high rainfall areas to drain
excess surface water, from areas
where water builds up, to troughs
lower down. It has a similar profile to
corrugated iron, with peaks 20 m
apart.
A
Describes how
excess water is
removed by the
selected
drainage
technique.
M
Evidence toward
A for Q2 (a)
available if new /
additional
information adds
to that answer.
Achievement with
Merit
TWO
(a)
Open drains are wide, mostly
boarded channels, which on sloping
land will intercept run-off (surface
water) and on flat land are used in
conjunction with tile drainage, which
directs water into open drains.
Tile drainage can be clay pipes or
plastic slotted pipes laid in a
channel 60 cm below the soil’s
surface. Excess gravitational water
drains downwards into and via pipes
to a lower-level drain.
(b)
Removal of excess water improves
milk production on dairy farms
 By increasing soil temperature,
which increases the rate of plant
processes. More pasture
consumed results in higher milk
production.
 A reduction in pugging means
more plant material will be
available for consumption,
resulting in higher milk
production.
Removal of excess water enhances
vegetable quality on vegetable
production units
 By discouraging the growth and
development of fungi, slugs etc,
which cause rot or chew foliage,
resulting in a loss of quality.
 Removal of excess water
increases root respiration,
providing energy for the growth
of healthy crops.
Removal of excess water helps
ripening of crops on cropping farms
 Poor drainage lowers soil
temperature, slowing plant
processes and growth rates,
resulting in delays in ripening.
Explanation links
the removal of
excess water to a
factor that impacts
on the aspect of
plant production
appropriate to the
selected technique.
Achievement with
Excellence
NCEA Level 2 Agricultural and Horticultural Science (90452) 2008 — page 4 of 5
Q
Evidence
Code
Achievement
A
Describes a benefit
that relates to how
the selected
technique assists in
the retention of soil
moisture.
M
Evidence toward A
for Q3 (a) available
for new / additional
evidence that adds
to the answer.
Achievement with
Merit
THREE
(a)
Mulching materials, eg straw:

Provide natural / artificial
surface cover.

Reduce evaporation of soil
water from the soil surface.

Kill vegetation that would
have absorbed soil water.

Decompose over time into
organic matter, thereby
retaining moisture.
Minimum tillage:
(b)

Leaves the soil structure
undisturbed, thereby reducing
air flow and evaporation.

spraying to kill vegetation
minimises transpiration /
losses.
Mulching materials help the soil
retain the moisture required for
photosynthesis and nutrient
uptake, both essential to plant
growth and development.
Production periods may be
extended, increasing overall
production.
Minimum tillage maintains soil
structure in light soils as the soil
is not subject to excess aeration,
or with oxidation of organic matter
that is normally low in lighter
soils. Maintenance of organic
matter will assist moisture
retention and nutrient returns,
providing essential inputs for
plant processes such as
photosynthesis, increasing
production.
Explains the link
between the
attribute of the
selected technique
and an essential
plant input /
process AND
increased
production.
Achievement with
Excellence
NCEA Level 2 Agricultural and Horticultural Science (90452) 2008 — page 5 of 5
Evidence
Code
Achievement
Achievement with
Merit
Achievement with
Excellence
eg
Rank order
(1) B – sprinkler Irrigation
(2) A – minimum tillage
(3) C – sowing drought-tolerant
crop varieties.
Sprinkler irrigation is the most
likely way of increasing
production levels, due to its ability
to provide water in the required
amounts at any time. As a result,
germination is assured and
fertiliser utilisation enhanced,
resulting in a doubling of yields,
improved product quality and the
ability to grow a wider range of
crops that have higher returns.
Although minimum tillage will
contribute to moisture retention,
soil structure and crop yield, it is
more effective at the time of
planting. It can influence only
water levels provided by rain, so
if not much rain falls, its influence
will be lessened.
Sowing drought-tolerant crop
varieties is not always possible,
as they are not available for all
plant species. While they may
survive in dry conditions, it does
not mean that they will produce to
the same level as crops receiving
regular irrigation.
A
OR
M
OR
E
Additional evidence
toward A for Q3 (a)
available for new /
additional evidence
provided to describe
minimum tillage.
Award A if a new
technique to
manage soil water
content is
described.
Additional evidence
toward M for
Q3 (b) available for
new / additional
evidence to explain
minimum tillage.
Award M if a new
technique to
manage soil water
content is
explained.
Justifies the order
of techniques by
explaining why one
technique is more
likely to increase
production in the
long term
compared with
ONE of the other
techniques.
Q
FOUR
Requires:
 1 valid
comparison
between TWO
techniques.
Judgement Statement – 2008
Agricultural and Horticultural Science: Describe how techniques used to modify soil water content
optimise primary production (90452)
Achievement
3A/M
Achievement with Merit
3M
Achievement with Excellence
1E
2M
plus
plus
2 other A / M
2 other A / M / E
Grades in brackets eg (A2) (E2) signal that evidence for another question in the paper has been recognised.