Jayachandran et al. (1998) recorded that under artificial shade (25 percent), ginger yield was 11 to 27 percent higher than in open fields, and even under 50 percent artificial shade the yield was better than under open conditions. Under natural shade in coconut plantation, there was a 32 percent increase in rhizome yield.
Another experiment (Sreekala, 1999) to study the effect of shade on biomass production and partitioning of photosynthates in ginger cv. Rio de Janeiro confirmed the preference of the crop to low-shade levels registering better growth and yield. Different shade levels (0, 20, 40, 60, and 80 percent) influenced the quality of ginger rhizomes. Volatile oil was more under higher shade levels in general (60 and 80 percent) while nonvolatile ether extract was higher under 20 percent shade (see Table 5.4). Starch as well as crude fiber content was more in plants grown under open conditions.
The photosynthetic rate and related parameters of ginger measured at 6 months after planting using a leaf chamber analyzer indicated that photosynthetically active radiation on the leaf surface as well as stomatal conductance were high under open conditions. But the leaf internal carbon dioxide concentration as well as stomatal resistance was high under heavier shade levels (60 and 80 percent). The photosynthetic rate as well as the transpiration rate was higher in plants grown in the open. Although, at 20 percent shade, the photosynthetic rate was less, the yield was high. This might be because of the photo-oxidation that has taken place at high light intensities or due to the inefficient translocation of photosynthates in open conditions compared to 20 percent shade (Ancy and Jayachandran, 2000). Ajithkumar et al. (2002) studied the effect of shade regimens on the photosynthetic rate and stomatal characters using the cv. Rio de Janerio. They found that the highest photosynthetic rate was in plants grown in the open conditions, followed by plants grown under 20 and 40 percent shade. The photosynthetic rate, stomatal conductance, transpiration rate, stomatal index, and stomatal frequency were significantly reduced linearly with increasing levels of shade. The yield increase under 20 and 40 percent shade compared to the open condition is attributed to be due to the higher leaf area under these shade levels.
Sreekala and Jayachandran (2002) worked out the influence of shade on physiological parameters of ginger. They reported higher dry matter accumulation, leaf area index, net assimilation rate and crop growth rate under low (20 percent) shade levels. (See Chapter 2 on Botany for a more detailed treatment of this topic.)
Radiotracer analysis done using labeled 14C has shown that under low-light intensity, the photosynthates translocated efficiently to the lower portion, whereas in an open condition efficient translocation did not take place. Studies have shown that a crop can tolerate shade up to 40 to 50 percent. Thus, partially shaded coconut gardens can be exploited for increasing the area under ginger.
Another screening trial conducted in Kerala for shade tolerance with 13 cultivars of ginger and the same set of shade levels confirmed the shade-loving nature of ginger, producing the highest rhizome yield and quality rhizomes at 25 percent shade. Cultivar Valluvanad was selected as the best single variety for all situations. The cultivars selected as suitable for each of the shade levels were Jamaica, Valluvanadand, Kuruppampady (0 percent shade), PS-667 and Jamaica (50 percent shade), Valluvanad, Jamaica, and Jorhat (75 percent shade) (Sreekala and Jayachandran, 2001). The cv. Rio de Janeiro raised as a pure crop and as an intercrop recorded highest dry matter production as intercrop in 6-year-old coconut plantation when compared to 2-year-old plantation. It appears that relatively low temperature combined with low-light intensity contributes to the development of more chlorophyll in ginger plants grown in shade, leading to higher photosynthetic rates (Sreekala et al., 2001). It can also be due to better utilization of photosynthates, as its degradation due to photorespiration has slowed down, because of a decreased respiration rate at a lower temperature.
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