Chemistry Reference
In-Depth Information
Resource capture and resource use efficiency
Greater grain yields of newer maize hybrids might have resulted in a concomitant increase
in resource capture and/or resource use efficiency.
In non-limiting environments, grain yield can be expressed as the result of intercepted
radiation, radiation use efficiency for shoot biomass production and harvest index [86].
Intercepted radiation did not consistently change in Argentinean maize hybrids released
between 1965 and 1993 [11], in accordance with the lack of a consistent trend with the year of
the hybrid release for shoot biomass. On the contrary, another study [40] reported
accumulated intercepted radiation increments for Argentinean maize hybrids released
between 1965 and 1997; which were attributed mainly to greater interception during the grain
filling period. Contrasting results between works could be related to period under study
and/or interaction between genotype and environment [87]. Nevertheless, grain yield
increments were attributed to a large extent to greater radiation use efficiency for grain yield in
both studies [11; 40]. The improved radiation use efficiency was not related to an improved
light distribution within the canopy, as a lower extinction coefficient was not evident with the
year of the hybrid release [40]. These results are in contrast to the more upright leaf habit with
the year of the hybrid release reported for US hybrids [31]. A greater radiation use efficiency
was also the main mechanism contributing to explain the greater shoot biomass of newer
Canadian maize hybrids [88]. A smaller decline in maximum leaf photosynthetic rate from
silking to maturity was the underlying process contributing to explain the greater radiation
use efficiency in newer Canadian maize hybrids [16;17; 89]. Maximum leaf photosynthetic
rates at silking, however, were similar among hybrids released in different decades [17].
In water and/or nitrogen limited environments, greater grain yields associated with resource
capture increments might have exposed current maize hybrids to more frequent nutrient or
water stresses. Nevertheless, as it was previously discussed, newer genotypes are more
tolerant to stresses than older hybrids. Grain yields of newer maize hybrids were greater
than those of older hybrids across
N levels
[31; 53; 90; 91]. Nitrogen use efficiency (the ratio
of grain production to soil available N) can be expressed as the result of nitrogen recovery
efficiency (NRE, the ratio of N uptake to soil available N) and nitrogen internal efficiency
(NIE, the ratio of grain yield to whole plant N uptake at physiological maturity). Nitrogen
use efficiency increased with the year of the hybrid release in Argentina during the 1965 -
2010 period [91; 92]. Nitrogen internal efficiency rather than greater N uptake largely
explained the greater N-use efficiency of newer maize hybrids than older hybrids [92; 93].
These results are in agreement with findings in Canada and US [94]. The greater N-use
efficiency in a newer than in an older Canadian maize hybrid was associated with a lower
rate of decline of leaf photosynthesis towards physiological maturity, under both high and
low N availability [17].
Water stress is one of the main limitations to crop grain yield worldwide; and it may reduce
maize grain yield by 12-15% in temperate regions [95, 96]. Grain yield of newer maize
hybrids was greater than that of older hybrids across
water regimes
during the grain filling
period [97]. Preliminary results of our group indicate that grain yield improvements in
