and increasing its vitality, and provides a good environment for vigorous growth of plants. Temperature decreases and humidity increases as a result of shading (Table 6.13).
Only proper shading can make soil humidity and soil water content harmonize and meet the growing requirements of ginger. Insufficient shading is ineffective. If the shading is excessive, the shoot growth becomes lanky with weak stems and thin leaves and leads to a yield decrease because of deficiency of light. Two years of experiments showed that 50 to 60 percent of shading is suitable for better growth of ginger (Shaohui and Zhenxian 1998, Xizhen et al., 2001) (Table 6.14).
Shading Methods: The traditional shading in the north of China is achieved by inserting straw (also called "inserting shadow straw"); that is, making a sparse fence with millet straw. Usually, three to four pieces of millet straw are made into a bundle on the south side (east to west line) or the west side (north to south line) of the ginger line. The fence height is around 60 to 70 cm, and it is slightly slanted to the north or east (Figure 6.10). About 6,000 kg/ha straw is required. Millet straw can be replaced by corn straw. Mountainous areas can use locally available materials. For example, tree branches are usually used in Laiwu City in Shandong province (Figure 6.11). Stilettoed black plastic film, sun-shading net, and other materials are gradually became common after 1995; they all have a good shading effect (Zhao and Ku, 1992, Xizhen et al., 2001).
In the south of China, shading sheds called "put up ginger shed" are usually used. These sheds are erected after buds sprout. Bamboo or sticks 2 to 3 cm thick are planted on both sides of the farmland, and then little bamboo staffs 1.7 to 2.0 m high are bound horizontally, covered with grass or wheat straw, and finally fixed with ropes (Figure 6.12).
Figure 6.11 Shading mode of Laiwu ginger.
For such shading, 6,000 pieces/ha of bamboo staffs and about 5,250 kg/hm2 couch grass are needed.
Other Modes of Lowering Temperature and Holding Humidity: Traditional shading methods are labor intensive and costly. Detailed research on the photosynthetic characteristics of ginger in recent years indicated the existence of certain photoinhibition phenomena under high light stress, which is a photoprotective mechanism for growth and development. The photosynthetic rate and carboxylation efficiency have not increased with shading, but decreased as the shading intensity increased. The main effect of shading is not only reduction in light intensity, but obviously it also reduces the soil temperature and air temperature around ginger plants and increases the water content of soil by reducing evaporation. Shading is very important to ginger growth. Two effective methods were developed through many years' research that can replace the present shading methods.
Covering with Straw on the Ground: After the planting, a layer of 3 to 5 cm thick wheat straw or other straw is spread evenly on the surface of the ginger bed. About 300 to 4,500 kg wheat straw is required per hectare. This method can save manpower and cost, is easy to do and also has a better effect of decreasing temperature and holding soil water than shading above the ground. It has improved the field microclimate better and promoted plant growth and development and, therefore, the yield was higher. But straws are very light-weight and can easily be blown away by wind (Kun, 1999b).
Black Plastic Film Mulching: This method of shading is achieved by stretching a double layer of black plastic film tightly over the ridge to cover it after planting. If the ridge was covered with transparent film after planting in the beginning of April, then one layer of black plastic film covering should be layered over the transparent film in the beginning of May. The film must be inserted into soil with the back of a sickle, keeping about 15 cm between the trench bottom and the film. One width of film can be used to cover two rows (the width of film is 1.1 to 1.2 m) or four rows (the width of film is 2.4 m). The results of the experiment showed that the film mulch was better for reducing temperature and holding soil moisture than shading aboveground with straw or other materials (see Table 6.14). Plants grew stronger obviously (Table 6.15), and the yield increased by 8 to 30.2 percent, the cost reduced by 1,230 to 4,725 Yuan/ha (Table 6.16), the economic benefit markedly enhanced, and there were no problems of being blown away. Because of these benefits, plastic film mulching is being popularized among ginger growers (Xianchang et al., 1995, Zhifeng et al., 2001).
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