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Ginger Growth Stages
Figure 6.3 Sketch map of ginger-growing stages. 1. Germinating stage. 2. Seedling stage. 3, 4. Flourishing growing stage. 5. Rhizome dormant stage.

Germinating Stage

The germinating stage starts when the dormant bud begins to sprout to the opening of the first leaf (Figure 6.4). This takes about 50 days. The nutrition for germination and rooting comes from the stored nutrition in the rhizome bud. So the size and nutrition of seed set has great influence on the growth of seedlings in subsequent stages.

Ginger Growth Stages

Figure 6.4 Germination process of ginger. 1. Sprouting stage. 2. Peel off stage. 3. Squama stage.

4. Seedling-forming stage.

The growing bud is very small in the germinating stage; only about 0.24 percent of the gross volume of the planting unit. But this period is the foundation of the henceforth growth. So it is necessary to select seed properly and create favorable conditions in order to produce good and strong seedlings (Zhao and Xu, 1992).

Seedling Stage: The seedling stage is from the first leaf opening to the stage at which the plant develops two tillers; a stage that is usually called "the three-ply forks" period, and it takes 60 to 70 days from planting. In this period, the nutrition is supplied by the seed rhizome at first, and is later absorbed and produced by the seedling itself. The growth consists of the primary shoot and root system. After seedlings come out of the soil, fibrous roots increase gradually and some small lateral roots are also produced, thus forming the main absorption root system. Under normal weather conditions, the primary shoots grow at the rate of 1 to 1.5 cm a day. At the end of the seedling stage, the dry matter of this shoot makes up about 66.8 percent of the whole plant. When the seedling period is over, most plants have two lateral tillers (primary tillers), therefore, it is called "three-ply forks" stage. The leaves grow slowly during the first 20 days of the seedling stage; one new leaf is produced every 3 to 4 days. A month later, the new leaves are produced quickly with the lateral tillers appearing and elongating, with about one to two leaves being produced every day. The leaves of primary shoot make up about 63.2 percent of the total at this stage, and the total leaves at the end of seedling stage make up 15.1 percent of the total leaves of the whole growing period.

The plant grows slowly in the seedling stage; the growing mass makes up 7.83 percent of the total. In this stage, in order to promote better growth, it is important to control weeds and give adequate care in order to make a sound foundation for the production of lateral tillers, rhizome formation, and enlargement.

Flourishing Growing Stage: The flourishing growing stage takes about 70 to 80 days from the "three-ply forks" to harvest. The plants in this period show quick growth. On the one hand, many tillers arise and leaf number and area increase sharply; on the other hand, the rhizome expands quickly. This period can be divided into two stages. From

"three-ply forks" to mid-September is the early flourishing stage, in which the plant still focuses on growth of the aerial shoot. Many tillers arise, the leaf area increases rapidly, roots grow continuously, and some fleshy roots are also produced. The rhizome has already formed, the rhizome branches producing fingers, but their growth is slow. After mid-September, the growth emphasis is shifted to the rhizome. At this time, the root quantity becomes stabilized, tillering speed decreases, and the leaf area reaches steady state. Photosynthates produced by leaves are mainly transported and deposited in rhizome. This stage is the rhizome-expanding stage. As to the growing conditions, the fertilizer and water availability should be maintained to promote plant development to form a strong assimilation system and ensure strong photosynthetic ability in the early flourishing stage. In the rhizome-inflating stage, maintaining the availability of nutrients and water are essential to prevent the premature senility of the stem and leaves that ensures a longer time for assimilation and development. Hence irrigation, fertilization, earthing up, and other measures to enhance the yield to the maximum should be practiced.

Rhizome Dormant Stage: Ginger cannot endure frost and is usually harvested before the first frost, which compels the rhizome into dormancy. When temperature rises again the next spring, it enters the next growing period.

Impact of Environmental Conditions

Temperature: Ginger originated in tropical Asia, and it prefers a warm, humid climate and cannot endure very low temperature. But by long-term cultivation, selection, and domestication, it has become adaptable to lower temperatures. Ginger can germinate below 20°C, but only slowly. The appropriate germinating temperature is 22 to 25°C. If the temperature goes above 30°C, germination is quick but the sprouts will be weak. In the seedling stage and the early growing stages, the suitable temperature is 22 to 28°C and that during the rhizome-enlarging stage is 25°C (Xizhen et al., 1998d). When the temperature drops below 15°C, ginger will stop growing and should be harvested.

Light: Ginger grows well under moderate light intensity. Studies have shown that the light compensation point of a single leaf is 20 to 30 ^mol m~2 * s_1 and its light saturation point is 660 to 820 ^mol m~2 * s_1. But the photosynthesis of the clump (whole plant) requires much higher light than that of a single leaf (Dewan et al. 1991, 1995, Xizhen et al., 1998c, 2000). It has been shown that the clump light saturation point has not been reached when the photon flux density reaches 1,180 ^mol m~2 * s_1. So higher light is required for the ginger clump in the field (Dewan et al., 1995, Kun et al., 2002, Xianchang et al., 1996).

The light intensity requirement of ginger varies in different growing stages. It requires darkness in the germinating stage, moderate light in seedling stage, and higher light in the actively growing stage. Ginger is not influenced by day length. It can form rhizomes regardless of long, short, or natural light conditions, although a natural condition is the best (Zhenxian et al., 2000).

Water: The ginger root system is poorly developed and grows shallow, so its waterabsorption ability is weak and the plant cannot endure drought. Under drought conditions, the plant becomes dwarfed, photosynthesis becomes weak and yield decreases. Moreover, more fiber may be formed in the rhizome and the quality becomes poor. Experiments have shown that the effect of soil humidity has a very significant effect on

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