NCEA Level 2 Agricultural and Horticultural Science (90452) 2007 — page 1 of 5
Q Evidence Achievement
Achievement with Merit
One
(a)
(i) Soil texture / structure: Sandy clay loam is prone to decreasing soil moisture content, hence the need for irrigation.
(ii) Plant ’s stage of growth: At this stage
(flowering and seed development), maize utilises the greatest amount of water.
(iii) Climate: From November onwards, evapotranspiration (ET) exceeds rainfall.
Correctly describes how
TWO of the three factors determine that irrigation is required at this time.
(b) Centre-pivot irrigation system
This consists of a galvanised steel lateral that rotates in a circle about a fixed point in a paddock. Water is pumped to the centre of the pivot, along the laterals and out of the sprinklers.
How the technique suits maize production
This system is high enough to go over the maize, and can travel on flat topography. It provides a medium-high water application rate (15 –75 mm / h) and uniform distribution.
There is limited damage to the crop by wheel tracks. Water use is minimised due to the efficient application, and not affected by wind.
Use of the system ensures that the maize crop is provided with its optimum water requirements throughout production without the soil becoming waterlogged. As a result, the crop will not experience water stress, and plant processes will function at their optimum rate, ensuring the crop produces a maximum yield.
(c) How irrigation at flowering / seeddevelopment stage increases crop yield
Maize needs an adequate supply of water
(7.5 mm) during the two weeks immediately before and after flowering. This ensures optimum rates of photosynthesis and nutrient uptake, leading to optimum cob and seed development. The number of flowers produced determines the number of seeds that can be produced and therefore pollinated. The more seeds pollinated, the higher the grain yield.
Along with warm temperatures, an optimum supply of water maximises growth-rates and even development of the crop. As a result, there will be higher maize yield.
Correctly describes a centre-pivot irrigation system.
Correct explanation.
Correctly explains how attributes of the technique best suit a tall crop by reducing physical damage and consequent crop loss.
OR
Correctly explains that regular water application means that the crop is not stressed, and plant processes critical to yield are optimised.
Achievement with Excellence

NCEA Level 2 Agricultural and Horticultural Science (90452) 2007 — page 2 of 5
Q Evidence Achievement
Achievement with Merit
Two
(a)
(i) Land-related factors

A sandy clay loam has a mixture of mainly sand and clay with some silt particles. It has medium levels of macro-pores to micro-pores, and therefore is generally free-draining in summer. However, when the soil is saturated, excess water cannot be absorbed and flooding occurs.

The flat topography also increases the likelihood of waterlogging.
(ii) Climate-related factors

From April –September, rainfall exceeds evapotranspiration (ET) and infiltration rate.
(b) How a surface drainage system removes gravitational water eg Gravity-fed open drains

Long rows of open ditches are dug out in a v-shape on paddock boundaries.
Excess water and water from larger pores is removed by the action of gravity over 2 –3 days after rain.
(c) How a surface drainage system maintains water levels at field capacity or below
After rain / irrigation, surface drainage will leave water only in the finer pores of the soil, which will not drain with gravity – this is field capacity. Water levels will subsequently gradually drop below field capacity over time.
(d) How the use of a drainage system could advance the time at which maize crops are harvested
Use of a drainage system improves soil aeration and temperature, allowing:
 better nutrient uptake
 aerobic organisms
 root and tissue development of the crop
 improved ability of the soil to carry stock or machinery.
Rotting of roots and the incidence of soilborne disease is reduced. A sound rootsystem results in increased plant process activity (water and nutrient uptake, photosynthesis), which increases plant growth.
Better plant growth will advance the harvesting time of maize.
Correctly describes ONE land-related and
ONE climaterelated factor that could cause the need for a surface drainage system.
Correctly describes the operation of a drainage system.
Correct explanation.
Correctly explains how drainage improves plant growth and thereby brings forward the harvesting time.
Achievement with Excellence

NCEA Level 2 Agricultural and Horticultural Science (90452) 2007 — page 3 of 5
Q Evidence Achievement
Three
(a)
Factors that reduce the availability of soil water include:
 the sand component of the sandy clay loam soil
 the higher levels of evapotranspiration
 lower rainfall.
(b) How strip tillage could improve maize production
Strip tillage causes less soil disturbance than other cultivation methods, as only 50% of the soil is affected. This reduces air movement and exposure to sun, which are both responsible for causing significant soil-water loss. Cultivation by strip tillage will allow air / water movement and extensive root-growth.
Increased root activity (nutrient uptake) must increase overall maize production.
Correctly describes ONE of the factors.
Achievement with Merit
Correct explanation.
Achievement with Excellence

NCEA Level 2 Agricultural and Horticultural Science (90452) 2007 — page 4 of 5
Q Evidence Achievement
Four Rank order
(1) C – Strip tillage
(2) A – Centre-pivot irrigation
(3) B – Surface drainage
This is the best order, but the presence of critical thinking in the candidate’s justification should be the driver of Excellence.
Strip tillage
Due to reduced working of the soil, there is less opportunity for soil water evaporation and therefore soil water deficit. Soil structure will be preserved, which provides good aeration, root-run and the ready entry of rainfall. It also increases the organic matter in the soil and reduces wind erosion. Strip tillage increases the soil temperature where the seed is being planted, therefore increasing the length of time available to the plant for growing.
This method is not a permanent technique and therefore is implemented only when necessary. Of the three techniques, it is the cheapest to implement. Strip tillage has been found to be more economical than conventional planting, as only 20% of the planted paddock has to be cultivated.
This technique is better than centre pivot irrigation and surface drainage because it allows an earlier sowing date so maize production can be maximised.
Centre-pivot irrigation
This would ensure that the water requirements of the maize crop were met throughout production, without soils becoming waterlogged. As a result the crop would not experience water stress and plant processes will function at optimum rates, ensuring the crop produces a maximum yield.
Centre-pivot irrigation would better meet the needs of maize plants than surface drainage.
Surface drainage
Due to Bellevue Farm having sandy clay loam soil, being relatively free-draining, and rainfall not exceeding ET during the summer months when maize is grown, drains are not required. They would only be useful in a flooding situation.
This method would not increase soil water content, as it is not effective during the summer months so will not contribute to a higher maize yield. Implementation of the other techniques would better ensure a highyielding maize crop.
Describes how
EACH of the techniques is used to modify the soil water content.
Achievement with Merit
Explains how
EACH of the techniques is used to modify the soil water content.
Achievement with Excellence
Justifies the rank order of techniques by explaining which best contributes to the production of a high-yielding maize crop.
The presence of critical thinking should be evident in the candidate’s justification of the selected technique.

NCEA Level 2 Agricultural and Horticultural Science (90452) 2007 — page 5 of 5
Achievement
3 x A
Achievement with Merit
Achievement plus
3 x M
Achievement with Excellence
Merit plus
1 x E