Agriculture Reference
In-Depth Information
Table 7.2  Minimum water allocation as a percentage of total water available to the manager
Growth stage (Lorenz et al.
1995 )
Minimum percentage
allocation
Recommended soil water
potential Ψ (kPa) for the
implementation of RDI
Budburst to flowering
9 %
> −30
Flowering to fruit set
6 %
> − 10
Fruit Set to veraison
35 %
− 80
Veraison to harvest
36 %
− 80 > Ψ > − 200
Harvest to leaf fall
14 %
> − 200
Dormancy
N/A
> − 30
1948 ). The reader is directed towards the seminal work of the FAO (Allen et al.
1998 ), the ASCE (ASCE 2002 ) and the ITRC (Burt et al. 2002 ). In these methods,
a reference (or the pan evaporation) is related to the grapevine water demand using
crop based coefficients throughout the growing season. The difficulty in using these
methods is the need to adjust the coefficients for site specific conditions such as the
use of mid row swards, the density of planting or the ratio of exposed undervine
bare soil. Typically, these methods are used for the creation of a water budget in or-
der to evaluate soil water depletion, and therefore identify what fraction of the soil
water reservoir the plant is extracting (Table 7.1 ). Water budgets can be “truthed”
using a range of commonly available soil moisture monitoring equipment over the
depth of the grapevine rootzone. Alternatively, irrigation can be driven directly us-
ing soil moisture sensors and the definition of thresholds based of the various soil
fractions (Table 7.1 ) for a given soil texture. Of particular interest of growers oper-
ating in regions where irrigation water is scarce yet necessary, is water budgeting on
the basis of the available water (such as water allocated via a commercial irrigation
scheme and dam water) rather than that required in order to ripen the crop. The
minimum water allocations are summarised in Table 7.2 (Beckingham et al. 2004 ).
Deficit irrigation strategies were developed to manage the growth of the canopy,
based on the hypothesis that smaller canopies intercept more light, leading to better
quality fruit with no or little impact on fruit yield (Kriedemann and Goodwin 2004 ;
Smart and Robinson 1998 ).
Two irrigation strategies are currently the subject of much research, namely Reg-
ulated Deficit Irrigation (RDI) and Partial Rootzone Drying (PRD). More strategies
have been suggested in the literature, such as Stress Deficit Irrigation (SDI) but are
not yet widely adopted.
Regulated Deficit Irrigation
Applying deficit irrigation after berry set and until veraison limits shoot growth
without limiting the number of berries per bunch, as this is determined at berry set
(Hardie and Considine 1976 ). Berry size at harvest is however reduced as berries
undergo a phase of cell expansion both before and after veraison (Coombe 1973 ).
Search WWH ::




Custom Search