Agriculture Reference
In-Depth Information
6000
5000
Y = 3667.15 + 35297.46X - 32654.09X
2
R
2
= 0.18**
4000
0.60
0.30
0.40
0.50
Grain harvest index
FIGURE 1.22
Relationship between grain harvest index and grain yield of lowland rice.
GHI values of 0.39 for pea (
Pisum sativum
L.), 0.37 for lentil (
Lens culinaris
Medik.), 0.41 for
chickpea (
Cicer arietinum
L.), 0.28 for mustard (
Brassica juncea
L.), and 0.38 for wheat grown on
loamy soil. Winter and Unger (2001) reported that sorghum GHI values varied from 0.39 to 0.45
depending on the type of tillage system adopted. Rice GHI values varied greatly among cultivars,
locations, seasons, and ecosystems, and ranged from 0.35 to 0.62, indicating the importance of this
variable for yield simulation (Kiniry et al., 2001). Rao et al. (2002) reported GHI values of soybean
ranged from 0.37 to 0.45 with a genotypic mean of 0.43. Rao and Bhagsari (1998) reported similar
ranges for GHI values for soybean grown in Georgia. Lopez-Bellido et al. (2000) reported that GHI
values for wheat varied from 0.41 to 0.45 (mean value of 0.44) depending on tillage methods, crop
rotation, and N rate.
The limit to which harvest index can be increased is considered to be about 0.60 (Austin et al.,
1980). Hence, cultivar with low harvest indexes would indicate that further improvement in parti-
tioning of biomass would be possible. On the other hand, cultivars with harvest indexes between
0.50 and 0.60 would probably not benefit by increasing harvest index (Sharma and Smith, 1986).
Genetic improvement in annual crops such as wheat, barley, corn, oat, rice, and soybean has
been reported due to improvement in dry weight as well as GHI (Fageria and Baligar, 2005).
Unkovich et al. (2010) reported that the GHI of crop plants has increased over time due to breed-
ing for higher yield. These authors also reported that the rate of GHI increase due to cereal breed-
ing in Australia is about 0.015 per decade, compared to about the 0.02 achieved in the United
Kingdom. Short-stature, modern crop cultivars have a higher GHI than their taller forebears,
although total dry matter production is most often very similar (Evans, 1993). A recurring theme
in GHI has also been a shortening of the vegetative growth stage of crop plants, providing propor-
tionately longer grain filling period (Siddique et al., 1989; Lopez Pereira et al., 2000; Unkovich
et al., 2010).
Peng et al. (2000) reported that genetic gain in rice cultivars released before 1980 was mainly due
to improvement in the GHI, while increases in total biomass were associated with yield trends for
cultivars developed after 1980. The cultivars developed after 1980 had relatively high GHI values
and further improvement in the GHI was not achieved. These authors also reported that further
increases in rice yield potential would likely occur through increasing biomass production rather
than increasing the GHI. Tollenaar et al. (1997) reported that the GHI values of corn were 0.41 at low
N rates (no added N) and 0.45 at higher N rates (150 kg N ha
−1
) across two hybrids. The GHI values
of 10 upland rice genotypes were influenced by N fertilization (Table 1.22). Overall, increases in
the GHI values were 19% at high N rates compared with low N rates. Similarly, Fageria and Santos
(2008) also determined GHI of 20 dry bean genotypes under two N levels (Table 1.23). The GHI of
these genotypes increased with the addition of N compared to control treatment. Overall, increase
