Maximum yield, Y max
At Ymax, grain yield is limited by climate and
genotype only, and all other factors are
nonlimiting. Y max fluctuates from year to year
(±10%) because of climatic factors. For most
rice-growing environments in tropical South
and Southeast Asia, the Y max of currently
grown high-yielding rice varieties is about 10
t ha -1 in the dry season (high solar radiation),
and 7–8 t ha -1 in the wet (monsoon) season,
when high humidity leads to greater disease
pressure and the amount of solar radiation is
smaller due to greater cloud cover.
Experimentally, Y max can be measured only in
maximum yield trials with complete control of
all growth factors other than solar radiation.
Important points:
Climate cannot be manipulated, but Y max
varies depending on the planting
(sowing) date.
Grow rice varieties adapted to prevailing
climatic conditions (i.e., select genotypes
with the highest Y max under a given
climatic regime).
Attainable yield, Ya
At Y a , grain yield is smaller than Y max due to
limited water and nutrient supply. In irrigated
rice, water is usually not a limiting factor
(except when the temperature of the irrigation
water is very high (i.e., geothermal influence)
or very low (i.e., at high altitudes), thus Y a
represents the attainable yield limited by