The most significant constraints to rice production in the Mediterranean climate areas includes: low
temperature, water scarcity, biotic stresses, unsatisfactory grain quality, high production costs and the
population’s concerns about the harmful effects of rice production on the environment.
As rice plants originate from subtropical and tropical zones, they are easily damaged by low
temperatures at any growth stage from germination to ripening. The cool weather and strong winds
during stand establishment in Mediterranean climate areas may cause partial stand loss and seedling
drift, which lead to poor crop establishment. In many temperate areas, the emergence rate quite often
does not exceed 30 to 40 percent of the planted seeds. Therefore, to achieve an acceptable crop
stand, rice growers usually use about 200 kg/ha of seed. This low rate of crop emergence is due
primarily to the effect of anaerobic conditions on germination occurring under low temperatures. To
avoid low temperatures during crop establishment stage, some growers end up with delays in crop
planting. However, a delay in crop establishment leads to the occurrence of reproductive stages of the
crop during periods of low temperatures during the autumn that causes the death of pollen cells at
meiosis stage and subsequent grain sterility. Poor crop establishment under Mediterranean conditions
could be overcome by developing new high-yielding varieties with good tolerance to low temperatures
during germination, better land leveling and water management.
Research on rice cropping systems carried out in Egypt has to face the great climate changes, and
the linked abundance of cultivated varieties, characteristic of the high latitudes-temperate areas where
rice is traditionally grown. Therefore, dynamic simulation models can provide a useful tool for system
analysis needed to improve the knowledge, the agronomic management and crop monitoring.
WARM (Water Accounting Rice Model) simulates yield of paddy rice (Oryza sativa L.), based on
temperature-driven development and radiation-driven crop growth. It also simulates; biomass
partitioning, floodwater effect on temperature, spikelet sterility, floodwater and chemicals
management, and soil hydrology. Biomass estimates from WARM were evaluated .The test-area was
Sakah, Kafrelsheikh (Egypt). Data collected from 2003 to 2012 from rice crop grown under flooded
and non-limiting conditions were split into a calibration (to estimate WARM model parameters) and an
evaluation sets. Plants were sampled during the life cycle from rice plots of two rice cultivars Sakha
101 and Giza 177, maintained at potential production, to determine some important crop variables
and parameters such as aboveground biomass (AGB), leaf area index (LAI), potential yield, specific
leaf area, and the date of the main phonological stages.
Results show that the model was able to simulate rice growth for both varieties. The assessment of
model performances has shown average of relative root mean square error (RRMSE) calculated on
AGB curves was above 50% for the calibration and 30% for evaluation sets. The modeling efficiency
(EF) is always positive and the coefficient of determination (CD) is always very close to 1.
Indeed, intercept and slope were always close to their optima and (R2) was always higher than 0.90.
The indices of agreement calculated for the evaluation datasets were better than the corresponding
ones computed at the end of the calibration, indirectly proving the robustness of the modeling
approach. WARM’s robustness and accuracy, combined with the low requirements in terms of inputs
and the implementation of modules for reproducing biophysical processes strongly influencing the year-to-year yield variation, make the model suitable for forecasting rice yields on regional, national
and international scales.
Shimaa A. Badawy
Department of Agronomy, Faculty of Agriculture, Kafrelsheikh University, Egypt.
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