Agriculture Reference
In-Depth Information
Flood and Furrow Irrigation
For flood irrigation, the mid-row area across to the mounded vine rows on each
sidecomprisesanirrigationbay.Waterlowingfromaheadchannelintothebay
coverstheentiremid-row.Suicientwatermustbeappliedforsoilatthefarend
of the bay to wet to a desired depth, which usually means that vines at the head of
the bay receive too much water. This uneven distribution is worse in long bays on
permeable soils—a problem compounded further by the presence of slight rises
andhollowswherewaterpondsandiniltrationisgreater.Laser-guidedgradingof
thelandwhenthevineyardisestablishedminimizesthisproblem.
In furrow irrigation, water is diverted from a head ditch into shallow chan-
nels,eitherononeorbothsidesofavinerow(igure4.30A),orsometimesinto
asinglemedianchannel(igure4.30B).Althoughfurrowirrigationsufersfrom
the same disadvantages as flood, both have the advantage of low capital costs and
permit the use of water that would be problematic for drip irrigation because of
suspended solids.
Furrow and flood irrigation are wasteful of water compared with drippers and
under vine sprinklers and are being phased out in most irrigated vineyards around
the world.
Monitoring Deep Drainage
Although capacitance or TDR probes can be used to monitor changes in soil water
content at depth, because water moves in response to a gradient in suction, grav-
ity,andosmoticforcescombined(notagradientinwatercontent),drainagecan
occur when changes in water content are small and undetectable by these probes.
Tensiometersplacedatthebottomoftherootzonearebestfordetectingdeep
drainage. As shown in table 4.2, the matric suction at the depth of the tensiometer
bulbisequaltothetensiometerreading(measuredinkPa)lesstheplacement
depthindecimeters(10-cmintervals).Amatricsuctionintherange0to1.0kPa
indicates that the soil is very nearly saturated and drainage is occurring.
heFullStopWettingFrontdetectorisanotherinstrumentcapableofdetect-
ingthemovementofawettingfrontatdepth(see www.fullstop.com.au) .he
FullStopdetectorisinstalledattwodepths—usuallyat0.3and0.5m—under
irrigated vines. A float rises when the matric suction at the funnel rim falls to 2
kPaorlessandabout20mLofdrainagewaterhascollectedinthereservoiratthe
base of the detector. Thus not only can the arrival of a wetting front be detected,
butawatersamplecanalsobecollectedforanalysis.AswiththeSoluSAMPLER
(seeigure4.24),NO 3 concentrations can be measured to check on any leaching
loss that might lead to groundwater contamination. Also, measurement of EC dw
(seebox4.11)atsuccessivetimesallowsanestimatetobemadeoftheamountof
drainage, provided that the depth of applied water and its EC are known.
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