The crop prefers light shade for good growth, but shade is not absolutely necessary. Jayachandran et al. (1991) investigated the effect of shade on the yield of ginger cv. Rio de Janeiro by growing plants under no shade (open) and 25, 50, and 75 percent shade. Shade was provided by coconut leaves spread on a pandal (shelter). At harvest (8 months after planting), the fresh rhizome yield was highest under 25 percent shade and lowest under 75 percent shade (20,093 and 10,778 kg/ha, respectively). The yield under open conditions was similar to that under 50 percent shade. Dry ginger recovery was highest under 25 percent shade (2,733 kg/ha).
Screening of ginger for shade tolerance was done with six cultivars (Maran, Kurup-pampadi, Himachal, Rio de Janeiro, Nedumangad, and Amballore local) under four shade levels (0, 25, 50, and 75 percent). This study confirmed the shade-loving nature of ginger, registering a significantly higher yield under different shade levels than under open, with 25 percent shade recording the highest value. The quality of ginger rhizomes improved when grown under shade. Based on the rhizome yield, the cultivars adapted to each of the shade levels were identified as Kuruppampadi and Himachal (0 percent shade), Nedumangad, Himachal, and Kuruppampadi (75 percent shade). Himachal was found to be adapted to all situations. Under natural shade of coconut, Amballore local showed better performance.
The response of ginger to different shade levels (0, 25, 50, and 75 percent) and mulching levels (7.5, 15, 22.5, and 30 t/ha) was studied by Babu (1993). The highest yield (22.8 t/ha) and dry matter production were recorded in a low-shade condition of 25 percent and at the mulch level of 30 t/ha. As the performance of the crop was better under shade than in an open situation, the crop was considered to be shade loving and suitable as an intercrop in coconut gardens (see Figure 5.6). The uptake studies showed that the fertilizer requirement for intercropped ginger in low shade levels will be 10 to 50 percent higher than that of a pure crop.
Ancy et al. (1993) studied Rio de Janeiro plants, grown under 0, 25, 50, or 75 percent shade (provided by dry coconut fronds) and supplied with fertilizers at 75, 100, 125, or 150 percent of the recommended rate of 75, 50, and 50 kg of N, P2O5, and K2O/ha. The volatile oil content was highest (2.19 percent on a dry weight basis) under 25 percent shade, and the NVEE content was significantly higher under 25 or 50 percent shade than under 0 or 75 percent shade. The rhizome fiber content was not affected by shade and fertilizer treatments.
Nath (1993) at Assam, India evaluated the effect of shade (provided by a pigeon pea crop) and rhizome treatment (1 percent formaldehyde) on rhizome rot caused by Pythium myriotylum using the cv. Tura. The highest yield was recorded in rhizome-treated plants grown in the shade for 150 days. The increased yield was mainly due to reduction of disease, as disease incidence was 45.8 and 41.3 percent respectively, in the control and rhizome-treated plants grown without shade and 19.4 percent in rhizome-treated plants grown in the shade. It is suggested that the temperature around the crop may have been reduced by shading and this could have ultimately suppressed the growth of fungus. Wilson and Ovid (1993) studied the effect of shade on growth and yield of ginger and observed that the average yield of ginger was highest (68.4 t/ha) under okra shade.
Ancy et al. (1998) noted that nutrient uptake increased with increasing fertilizer rate under all shade intensities but the response in terms of rhizome yield per unit increase in fertilizer rate was highest under 25 percent shade followed by 50, 0, and 75 percent shade. Dry rhizome yield was highest (3,415.25 kg/ha) under 25 percent shade with nitrogen, phosphorus, and potassium (NPK) at 150 percent of the recommended rate.
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 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. 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. 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 l4C 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). 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. 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.
E. V. Nybe and N. Mini Raj “Ginger Production in India and Other South Asian Countries” (2005)