Summary. Sustainable irrigation guidelines that maximise
profitability and minimise water losses and accession to the watertable are
required for the new Ord Sugar Industry. In addition, knowledge on crop water
requirements is needed to guide water allocation and costing policies for the
expanding Ord Irrigation Area where sugarcane is likely to be a dominant crop.
Field data indicating water requirements for sugar in the Ord Irrigation Area
are few and this paper deploys a modelling approach to extrapolate from
knowledge of water requirements in other parts of the world. The approach
links long-term climatic data with soil water characteristics of the main soil
type, with a cropping systems model, to develop indicative estimates of
irrigation water requirement and yield consequences for different management
options for sugarcane production in the Ord.
Analyses of the growth of 12-month old ratoon crops were conducted using the
APSIM–Sugarcane model with historical climatic data from 1960 to 1985
and either a deep (188 mm available water to 160 cm depth) or shallow (144 mm
of water to 120 cm depth) Cununurra clay soil. Under maximum attainable growth
conditions where crops were irrigated after half the soil water supply was
depleted, average sucrose yield ranged from 26.7 to 29.0 t/ha, and the
irrigation requirement (assuming 100% application efficiency) ranged
from 22.7 to 23.8 ML/ha depending on ratooning date. Soil water holding
capacity had a major effect on the number of irrigations and the interval
between irrigation for a given irrigation schedule but little effect on yield
or irrigation requirement. Varying the irrigation schedule by changing the
level of soil water depletion before irrigation and thus the irrigation
frequency, showed the tradeoff between yield and irrigation requirement with
the most profitable irrigation schedule depending on the price of sucrose and
the cost of irrigation relative to other costs. Most of the year-to-year
variation in irrigation water requirement could be explained by the highly
variable effectiveness in soil storage of rainfall which ranged from 44 to
93%. This study has provided insight and indicative estimates of the
yield and irrigation requirements for different irrigation management options
for use in the establishment of an Ord River sugar industry. These estimates
will be further refined as field data become available.
Forecasting daily net irrigation requirement maps of India using an ArcGIS toolbar
