Agriculture Reference
In-Depth Information
Box 4.10 Use of a Soil Water Deficit to Implement Irrigation Scheduling
If soil monitoring is used, the profile water content is measured at regular
intervalsduringspringthroughsummer(automatedsystemsmayprovide
watercontentreadingsonanhourlybasis).Asindicatedinbox4.8,the
SWD
is
calculated as the difference between
FC
(inmm)andtheproilewatercontent
(inmm)oneachoccasion.Figure4.17showedtheseasonaltrendin
SWD
,
calculated in this way, in a nonirrigated block of vines growing on the clay loam
soil of table 4.3.
Whentheaccumulated
SWD
reaches a threshold value, which might be set
at the
RAW
plus half
DAW
to the depth of interest, the trigger point for irrigation
is reached. Figure B4.10.1 shows the effect of RDI, applied from fruit set to
veraison, in managing the
SWD
in the same vineyard as shown in figure 4.17 but
on a separate block of vines. Because there was little rain from January to March,
this period was suitable for applying RDI. The changes in
SWD
and timing of
irrigation are shown in the figure.
100
0
20
Bud break
80
Harvest
Veraison
40
60
FloweringFruit set
60
40
80
20
100
120
0
−
20
140
−
40
160
180
Irrigation
applied
−
60
−
80
200
Date
Figure B4.10.1
Changesinsoilwaterdeicit(
SWD
)duringoneyearforSauvignon
Blanc vines under regulated deficit irrigation in a cool-climate vineyard.
Withirrigation,the
SWD
waskeptinthereadilyavailablewaterrange(0to
39mm/60cmdepth)untilfruitset,theninthedeicitavailablewaterrange(39to
58mm/60cmdepth)uptoveraison.hetotalwaterappliedwas298mm.Rainfall
(solidline);
SWD
(dashedline).DatesareinU.S.format.(Originaldatacourtesy
ofDr.LilangaBalachandra,UniversityofMelbourne,Australia.)
(continued)
