Agriculture Reference
In-Depth Information
Table 10.1. Factors affecting crop growth and development and their sensitivity to
water and nitrogen deficits.
Growth Rate
Development (Duration)
Mass
Expansion
Phasic
Morphological
Principal
environmental factor
affecting the process
Solar radiation
Temperature
Temperature,
photoperiod
Temperature
Degree of variation
between genotypes
Low
Low
High
Low
Sensitivity to water
deficit
Low-Stomata
Moderate-Leaf
wilting and
rolling
High-Vegetative
stage
Low-Grain filling
stage
Low-Delay in
vegetative stage
Low-Main stem
High-Tillers and
branches
Sensitivity to nitrogen
deficiency
Low
High
Low
Low-Main stem
High-Tillers and
branches
Source:
Ritchie and Alagarswamy (2002).
process of estimating total biomass using crop growth rate and duration and parti-
tioning that biomass into harvested components. Separating growth and develop-
ment processes also allows a distinction between sources and sinks of assimilate
(i.e., photosynthetically produced carbon) within the various plant organs. A plant
can be exposed to source or sink limitation during its growth cycle, where “source”
refers to the production of organic matter by photosynthesis, and “sink” refers to
the assimilation of that organic matter in tissues. The assimilates are stored in roots
or elsewhere if the sink demand is less than source supply, as the aboveground plant
parts cannot grow faster than the sink demand. During seed development, stored
assimilates become available to augment daily grain fill demand.
Table 10.1 summarizes the environmental factors that influence crop growth and
development and the sensitivity of these processes to water and N deficits. In the
next sections, we discuss the three major processes—growth, development, and
yield and yield components—important in simulating crop yield.
Crop Growth
Net photosynthesis is simulated in functional models using radiation use efficiency
(RUE), which assumes that daily biomass production is directly proportional to inter-
cepted photosynthetically active radiation (IPAR), a concept introduced by Monteith
(1977). Model simulations need to consider variations in the RUE proportionality
constant over the time interval measured (hourly, weekly, or seasonal), the form of
biomass measured (aboveground, belowground, or specific plant part), and the type
of radiation measured (i.e., total solar or photosynthetically active radiation).
Accurate leaf area index (LAI) estimates are crucial for models based on IPAR.
Since LAI is the ratio of plant leaf area to the average ground area covered, it can
change dramatically over the growing season until a full plant canopy has developed.
