is a common outside environment directly impinging on the intensive
farm system. The following are the important factors to consider when
evaluating irrigation land:
irrigation requires soils with suitable characteristics. The most
desirable characteristics are:
- the ability to
allow water to enter - infiltration
- high water
holding capacity - available soil water capacity
- good internal
- a high degree
of uniformity of soil type.
irrigation of a poor soil may be economical in the short run but can
be uneconomical in the long run. Such soils can lower long run
profits in a number of ways such as reducing maximum yield, requiring
expensive remedial treatments (eg gypsum application, deep ripping,
drainage) and resowing after surface crusting has caused emergence
more uniform the soil, the easier it is to manage. If it is necessary
to cut and fill, the soil should be examined to the depth of the
maximum cut to judge the likely effect on production.
available soil water capacity
means the process of water entry into the soil and adequate
infiltration is vital for successful irrigation. It is determined by
soil type and texture. Sandy soils have the highest infiltration
quality. Some clay soils such as black basalts, have a high short
run rate of infiltration because of cracking but this attribute
disappears during cooler and wetter weather. Although the topsoil is
of major importance in determining the infiltration rate, the nature
of the subsoil is also important.
drainage under irrigation is essential. It is achieved by careful
planning and consideration of the surface drainage in the land
preparation and by choosing a soil with good internal drainage.
gained on older developed irrigation areas clearly indicate that
subsoil drainage ultimately becomes necessary. Therefore, irrigation
land should be of soil types known to respond to subsoil drainage
with contours enabling the provision of mains and outfalls for the
disposal of both subsoil and surface drainage waters.
is common for the irrigator to experiment with watering systems
particularly on different soil types. Therefore, the valuer on
inspection, should not accept that all the land being irrigated is
suitable for irrigation.
should seek the expert advice from soil conservation, irrigation and
water authorities and use soil maps when determining the area of a
farm suitable for irrigation. The aim of irrigation, whether flood,
drip or spray is to supply sufficient water to the soil so as to
provide an optimum amount of moisture within the soil at the plant's
most obvious benefit is the increase in crop yield but to achieve
this on a more less continuous basis requires a highly skilled level
of management. All soils were not designed by nature to cope with a
continuous supply of moisture. Otherwise irrigation soils would have
the spongy nature of many tropical and subtropical soils which
regularly have to cope with copious rain. If the farmer imposes a new
moisture regime on many soils he/she needs to have a good knowledge
of what will happen to the moisture in the soil in the long run.
most important part in analyzing a sale of irrigated land is to
determine the added value caused by the availability of water to the
property through irrigation. Generally, in irrigation areas (such as
the Murrumbidgee Irrigation Area) there are a large number of
irrigated farms and the area is comparatively, densely settled.
farms on the Murray River in South Australia and Victoria. Therefore,
the other factors affecting value such as the availability
and reliability of power, transport, proximity to markets are
constant making it easier to isolate the added value caused by
irrigation. Sale analyses can show irrigated lands having a value
about ten times the value of equivalent dry land.
The added value is a function of:
- A lower risk to
the expected future income and benefits occasioned by irrigation. That
is, comparatively immune from the effects of drought.
- The ability to
utilize an intensive land use on an irrigated farm which would have
been impossible on a "dry" farm. For example, vineyards.
FACTORS AFFECTING THE VALUE OF IRRIGATED FARMS
well as the above, the following valuation factors are applicable to
the valuation of irrigation farms:
- the viability
of the irrigated land use in the district. this will often be subject
to fluctuations in demand from overseas markets.
- the response of
soils to long term watering for example, salt and pan problems may
simultaneous provision of channels and drains as distinct from channels
- provision of
access crossings over channels and drains
- the extent,
frequency and degree of the supply of water. can the allowable quota be
transferred to other parts of the property if required?
- the value and
character of the dry land adjoining. the concept of synergy
means that drylands abutting an irrigation farm are worth more than
large tract of land subject to irrigation for the first time will not
command as high a price as land in an established irrigation area.
First time irrigated or newly occupied irrigated areas (a “pioneer”
land use) are deemed risky by the general market whereas established
districts are "proven" or "safe". Further,
whether or not there may be degradation through a higher water table
is not yet known.
first 10 years of a new irrigation district are critical in proving
the viability of irrigation compared to adjacent dryland farming.
effective crop root depths
loss of moisture by evaporation and extraction
is called evapotranspiration. Upon the
completion of an irrigation application there is an appreciable
amount of water on the foliage that evaporates into the air. The
saturated surface of the soil evaporates at much the same rate as
does a free water surface. After that, the moisture loss from the
soil is by way of plant extraction. Crop factors are a general
measure of the behaviour of different types of plants in this regard
when compared to the evaporation from free water surface. Drip
irrigation is the superior method in this regard having the lowest
rate of evapotranspiration.
example of the use of the crop factor and the evaporation figure to
determine the total moisture requirement is as follows:
requirement = monthly figure of evaporation * the crop factor
the crop factor = .75 and monthly figure of evaporation = 15 cm:
requirement = .75 * 15 cm = 12cm
12cm is the amount of moisture which must be incorporated into the
root zone of the crop to achieve optimum growth, either by rainfall
or irrigation or a combination of both. Because some of the water
applied, particularly by spray irrigation, will evaporate before it
can enter the soil, it is necessary to apply an additional amount to
compensate for this loss. When climatic conditions of high
temperature, low humidity and strong winds occur, the calculated
amount should be increased by 20%. For conditions of low
temperature, high humidity and light winds the calculated amount can
be increased by 10%.
topography is necessary for good drainage. Some land may be above the
head of water and therefore, cannot be irrigated without pumping and
storage. Therefore, the valuer has to ascertain not only the area of
land allowable to be irrigated under the water licence but also
whether or not it is suitable for irrigation. An irrigation farm with
poor drainage will lose value over time through increased salinity
a rising water table.
costs are higher on irrigation farms compared to equivalent dry farms
because of the problems of access, moving equipment and manpower over
the property. That is, good access to all irrigated parts of the farm
cost of preparation is a factor of:
- The nature of
the land after clearing. For example, is it rough, undulating, or level?
- The type of
irrigation systems are levelled with a gradient of between 1:500 to
1:2000. The steeper grade is used for quick watering (for example, on
pastures) and the lower grade for systems requiring good drainage but
deeper and longer water penetration (for example, row cropping). The
degree of development is similar to the preparation of dryland for
cultivation although the clearing is more radical (eg no shade
timber). Further, the ground is ripped deeper but otherwise the
marginal cost of land prepared for irrigation is small.
work is quoted on the basis of the amount of soil to be removed. To
prepare a perfectly level site of 0.4 ha which is required to have
about 20 cm fall in 200 metres (ie 1:1000) requires the movement of
about 103 cubic metres.
dryland complements the primary land use of the irrigated lands.
Therefore, the adjoining dryland has more value than if it was used
as dryland alone. This is an important principle in rural valuation
and applies to other inferior adjoining lands. For example, adjoining
"rough" land used as "relief grazing" and lambing
paddocks complements good grazing and arable lands.
sprinklers and furrow irrigation are being steadily replaced by
undervine systems which use much less water.
channels to deliver irrigation water to farms are being replaced with
low pressure pipe main systems.
SCALE PRIVATE IRRIGATION SCHEMES
are very few private schemes in Australia and only one large private
scheme in Victoria. In this case, a company of adjoining landowners
was formed to divert water from a storage reservoir by pumping into a
large distribution channel passing through neighbouring properties to
the point of delivery. Such schemes are generally, uneconomical and
create a number of legal problems in relation to ownership and
maintenance. In NSW an example of a private scheme is the Moira
Irrigation Scheme situated between Deniliquin (NSW) and Echuca
(Victoria). It covers about 60 farms over about 10 000 ha.
EXAMPLE: THE WESTERN DIVISION OF NSW
in the Western Division of NSW is carried out at Bourke, Menindee and
the lower Murray-Darling near Wentworth, Euabalong and Hillston.
Smaller irrigation areas exist on the Barwon and mid Darling rivers
and on smaller streams such as the Narran, the Culgoa system, the
Warrego and the Bogan rivers. Although the western division is
predominantly a pastoral area there is a trend towards irrigated cash
crops such as sorghum, oilseeds and cereals.
crop and pasture irrigation fluctuated during the early and mid 20th
century with modern large scale irrigation becoming established over
the last decade or so. During and immediately following severe
drought in the mid 1960s irrigation blocks usually of about 160 ha
were developed on some grazing properties with frontage to permanent
rivers. Inexperience with irrigation, cost increases and poor prices
for livestock have either closed many of these blocks or forced a
change to cash cropping.
the mid 1970s experienced farmers from beyond the Western Division
conducted successful cash cropping irrigation enterprises. Broadacre
irrigation is largely concentrated at Bourke, Menindee, the lower
Murray-Darling near Wentworth, Euabalong and Hillston. Lesser areas
are found on the Barwon and mid Darling and on the smaller streams
such as the Barran, the Culgoa system, Warrego and Bogan. Isolated
small plots generally up to 20 ha are found around bores or ground
production, chiefly of citrus, vines for various purposes and
vegetables has enjoyed a more stable and successful history. The
lower Murray-Darling development was initiated by the Chaffey
Brothers in the 1890s. Smaller horticultural areas are found at
Menindee, Bourke and Hillston. Isolation and aridity offer the
irrigator both advantages and disadvantages compared with the more
traditional irrigation areas. Being arid, water requirements are more
important and and frequent. However, irrigation allows greater
control over the farm environment and therefore reduces risk.
has reduced the frequency of floods and cultural and harvesting
operations are less likely to be impeded by rainfall. Isolation
provides a buffer against a number of diseases and pests (eg for pure
seed production). However, freight costs are higher and the services
of both the government and agribusiness are more difficult to obtain.
the Murray and the Darling downstream of Menindee lakes have assured
water. Elsewhere irrigators do not have the advantage of headworks
to ensure water availability and therefore, large scale irrigation
has concentrated in safer areas.
lower reliability is compensated by less risk of heavy rain, floods
or mouse plagues that have caused severe losses on the Namoi,
Macquarie and Murrumbidgee-Murray areas in recent years. Long hot
summers results in high evaporation but the longer growing season
allows greater flexibility. Horticulturists particularly, can obtain
high prices for early or out of season produce.
the Western Division has been held in extensive home maintenance
grazing leases so that prospective irrigators have had to purchase a
large property to obtain agricultural land. There is very little
suitable freehold land available in the Western Division.
Bourke cotton is a cash crop of great importance. Irrigated grain
production of both summer coarse grains and winter cereals are also
important. However, the need for cartage of over 200 km to the Grain
Handling Authority (GHA) at Nyngan detracts from profitability.
wide range of vegetables have been grown by market gardeners and
broadacre farmers for both the fresh market and processing. Bourke
has great potential for high quality processed potatoes. There is
little pasture and forage production being mainly, sorghum, cereals
and lucerne for hay.
wheat is a major crop at Euabalong with smaller areas of sunflower
and grain sorghum. The total area fluctuates around 1 500 ha. The
Hillston area has some 4 000 ha of irrigation including about 500 ha
using bore water. Most land is under pasture but 1 200 ha of cash
crops are grown, 1 000 of which is sorghum.
irrigation farms and market gardens have been a feature of Menindee
for many years supplying both Broken Hill and capital city markets.
The total area is about 140 ha, half of which was planted to various
tree and vine fruits. New large scale flood irrigation currently
using 4 000 ha is laid out on the bed of Lake Tandou southwest of
Menindee where winter cereals, coarse grains and oilseeds are grown.
The concept of irrigation on lake beds or alternatively sowing crops
into mud left by receding lakes is creating more interest in the mid
and lower Darling.
most important Western Division irrigation area is the lower
Murray-Darling with about 15 500 ha in the shires of Wentworth and
Balranald. This exceeds the total of the remainder of the Western
Division. Fruit, vines and vegetables use about half of the irrigated
area. Grape vines occupy about 2/3 of this and citrus makes up most
of the remainder. There are interesting and promising developments
in avocadoes, normally only grown in the tropical coastal climates.
produce is sold mainly in Melbourne and to a lesser extent Adelaide
markets. Spray irrigation is used for most of the lower
Murray-Darling for fruit and vegetables. Furrow irrigation
predominates on all other Western Division irrigation farms. The
remaining lower Murray-Darling irrigation is devoted to winter cereals
and pasture and only small areas of summer crops. The
irregular nature of most Australian waterways has prevented the
development of large private irrigation schemes which are found in
the USA and nearly all irrigation uses water supplied by government
in most cases is by way of open channels carrying the water at a
level to irrigate by gravity. These channels are supplied from the
streams by diversion weirs to raise stream level for example, the
Goulburn Weir, Yarrawonga and Torrunbarry Weirs on the Murray.
murrumbidgee irrigation area
Murray Valley – South Australia
AND SALINITY PROBLEMS
land is irrigated, it is usually necessary to dispose of surplus
water. In the early years of the highlift irrigation areas, seepage
shafts or deep bores were used. The lessee would install a system of
tile drains through the area of his holdings affected by seepage and
these drains would enable the surplus water to gravitate to the
shafts and bores. This method of disposal of drainage water was
successful for a while but had limitations which necessitated the
provision of comprehensive drainage schemes.
typical drainage scheme consists of a system of main drains which
collect water from the lessee's tile drains and transport it to
receiving structures known as drainage caissons. From these the water
is pumped to evaporation basins on the river flats. They are
periodically flushed out in times of high river flow.
levels in the Murray have been increasing in recent years. One of the
major reasons for this is that surplus irrigation water raises the
level (water table) of the naturally highly saline ground water thus
increasing it flow into the river.
salinity levels (above 850 EC (electrical conductivity)
units) will damage a number of irrigation crops and over a long
period, trees and vines will die through saline toxicity. The use of
undertree irrigation systems lessens the effect of salinity on
plantings but the problem of surplus water disposal exists. The
Engineering and Water Supply Department (EWS) of South Australia in
association with the Commonwealth has funded research into ways of
combating these problems.