Agriculture Reference
In-Depth Information
1989). In this case, the source (photosynthesis by leaves) may be the limiting factors. In other words,
the photosynthetic capacity of a plant will not be able to properly fill the large number of grains
produced per unit area or plants.
In legumes, the yield is mainly expressed as the product of pods per unit area or per plant, seeds
per pod, and seed weight. Grain yield in legumes can be computed by using the following equation
(Fageria, 2009):
Grain yield (Mg ha
−1
) = number of pods × number of seeds per pod
× weight of 1000 seeds (g) × 10
−5
Based on the above equation, Fageria (1989) calculated or discussed the yield of cowpea using
the following yield components: number of pods per unit area or m
−2
= 155; number of seeds per
pod = 7; weight of 1000 seeds = 140 g. Putting these values of yield components in the above equa-
tion, the yield will be
YieldMg ha
(
−
1
or metric ton ha
−
1
)
=×××=
155
7141
00
−
5
15
.
Studies have reported mechanisms of high grain yield in super-high-yielding rice (Xiong et al.,
2013). It was reported that in several field studies, some super-high-yield rice cultivars produced
6.4-20% higher grain yield than ordinary rice check cultivars (Wang et al., 2002; Wu et al., 2007).
The high grain yield of super-high-yield rice was attributed to large sink size (Wu et al., 2007;
Zhang et al., 2009). The sink size can be increased by increasing the panicle number per unit area
or spikelet number per panicle or both (Ying et al., 1998). It was also reported that super-high-yield
rice had increased biomass production, high leaf area index (LAI), during the grain filling period,
longer leaf area duration, a higher photosynthetic rate at the single leaf level, slower leaf senescence,
and the tolerance of photoinhibition as compared to ordinary rice (Chen et al., 2002; Katsura et al.,
2007; Lin et al., 2002; Wang et al., 2005, 2006, Zhang et al., 2009).
1.2.1.1 Plant Height
Plant height is the distance from the ground level to the tip of the tallest leaf for seedlings or juvenile
plants. For mature plants, it is the distance from the ground level to the tip of the tallest panicle,
ear, or head in cereals and branch legumes. Short and sturdy culms, more than any other character,
favor lodging resistance. Lodging is the permanent displacement of the stems from their upright
position. There are three types of lodging: breaking of the stem, bending of the stem, and rolling, in
which the whole plant is uprooted from the ground and falls over (Fageria et al., 2006). A tall crop
variety has greater bending moment than a short one because of culm height. Early lodging of long,
thin culms disturbs leaf arrangement, increases mutual shading, interrupts transport of nutrients
and photosynthates, causes grain sterility, and reduces yield (Jennings et al., 1997). Further, strong
winds and rains during reproductive and grain filling stages of growth can cause lodging in annual
crops. Lodging during the grain filling growth stage can reduce grain quality.
A short and sturdy culm also promotes favorable grain-to-straw ratios, adequate N responses,
and high yield capacities. Increased N application is essential for higher yields, but causes elonga-
tion of the lower internodes, making the crop more susceptible to lodging. In addition, planting date,
row spacing, and seeding rate affect lodging in soybean (
Glycine max
L. Merr.) (Willmot et al.,
1989) as well as plant height, branch production, and basal pod height. A marked increase in har-
vest index and grain production per day has been associated with reduced plant height and earlier
maturity (Evans et al., 1984). The heritability of dwarfism in cereals is high and is easy to identify,
select for, and recombine with other traits. While yield gains due to the introduction of dwarfing
genes into cereals have been remarkable, little evidence exists for concomitant improvements in
photosynthetic rate, crop growth rate (CGR), or kernel weight.
