Agriculture Reference
In-Depth Information
leaf N contents and decreased curvilinearly with decreasing leaf N content below the saturation leaf
N content.
1.2.6 I
mproves
G
raIn
h
arvest
I
ndex
GHI is the ratio of grain yield to total biological yield. This index is calculated with the help of the
following equation:
grainyield
grain+strawyield
GHI =
The values for GHI in cereals and legumes are normally <1. Although GHI is a ratio, it is some-
times also expressed in percentages. GHI is an important trait in improving grain yield in cereals
and legumes. The term GHI was introduced by Donald (1962), and since then has been considered
to be an important trait for yield improvement in field crops. Donald and Hamblin (1976) discussed
relationships between GHI and yield, and concluded that this was an important index for improv-
ing crop yields. Fageria et al. (2011b) studied the relationship between GHI and grain yield in low-
land rice under greenhouse conditions (Figure 1.21). The relationship was significant and quadratic.
Sixty-eight percentage variation in grain yield was due to GHI. Similarly, the author also studied the
relationship between GHI and grain yield of lowland rice under field conditions (Figure 1.22). The
relationship was significant and quadratic between these two traits. Generally, GHI has positive asso-
ciations with grain yield (Rao and Bhagsari, 1998; Rao et al., 2002), and N is important for improving
GHI. Fageria and Baligar (2005) have reported that GHI is an important trait in improving the grain
yield of annual crops. N deficiency and N excess affect assimilate partitioning between vegetative
and reproductive organs in crops (Donald and Hamblin, 1976).
Thomson et al. (1997) reported greater seed yields of faba bean with higher GHIs. Morrison
et al. (1999) examined physiological differences associated with seed yield increases of soybean in
Canada within groups of cultivars released from 1934 to 1992. These authors concluded that the
increase in the seed yield with the year of release was significantly correlated with increases in the
harvest index (0.5% per year), photosynthesis, and stomatal conductance, as well as decreases in
LAI. They further concluded that present-day cultivars are more efficient at producing and allocat-
ing carbon resources to seeds than were their predecessors.
Snyder and Carlson (1984) reviewed GHI for selected annual crops and noted variations from
0.40 to 0.47 for wheat, 0.23 to 0.50 for rice, 0.20 to 0.47 for bunch-type peanut (
Arachis hypogaea
L.), and 0.39 to 0.58 for dry bean. The GHI values of modern crop cultivars are commonly higher
than old traditional cultivars for major field crops (Ludlow and Muchlow, 1990). Cox and Cherney
(2001) reported average GHI values of 0.50 for 23 forage corn hybrids. Miller et al. (2003) reported
20
15
10
5
Y = -2.0710 + 81.5122X - 82.8806X
2
R
2
= 0.6832**
0.60
0.20
0.40
0.50
Grain harvest index
FIGURE 1.21
Relationship between grain harvest index and grain yield of lowland rice. (Adapted from
Fageria, N. K., A. B. Santos, and A. M. Coelho. 2011b.
J. Plant Nutr
. 34:371-386. With permission.)
