Soil relative humidity 80% 60% 40%

Figure 6.5 Effect of soil water content on ginger yield (Kun, 1999b).

the growth and yield of ginger. When the soil relative water content is in the range of 40 to 80 percent, the growth parameters such as plant height, tiller number, and leaf area increase with the increasing of soil humidity. If soil water is low and cannot meet the demands of the plant, the yield decreases drastically (Figure 6.5). But ginger cannot endure waterlogging either. Waterlogging affects the growth and development of ginger, and leads to ginger rot, which will lead to a severe yield reduction. So a supply of an optimum quantity of water in the growing season is important to guarantee better plant growth and higher yield

A ginger plant differs in its water requirements in different growth stages. In the seedling stage plants grow slowly and have little growth of biomass, so they need little water. But if the climate is hot and dry in this stage, the soil water evaporates quickly, the water metabolism of the plant is vigorous, and its transpiration rate will be high. So plants in the seedling stage are weak and unable to fight a drought. Thus, enough water should be ensured during this stage in order to avoid growth retardation. If water requirements are not met, the leaves often show the "roll up pigtail" symptom, plants grow slowly, photosynthesis is weak, and the yield will decrease drastically. During the active growing stage, the biomass is increased greatly; so the plants require more water. The soil should be moist and the relative water content should be kept to 70 to 80 percent.

Soil: Ginger is not very strict about soil texture and can grow well on arenaceous, loam, or clay soils; however, soil texture has a great influence on yield and quality. Loam soil is loose and with good aeration. It can hold water and nutrients. So it is beneficial for the growth of seedlings and the development of the root system. Therefore, the yield of the rhizome is higher and its quality is better when ginger is grown in loamy soil.

Ginger is sensitive to the pH of soil, especially in the active growing stage. The soil pH has a significant influence on the growth of aerial shoots as well as on the rhizomes (Table 6.2). Ginger is fond of slightly acid soil and can grow well in soils with a pH of 5 to 7. If the pH is more than 8, growth is retarded.

Mineral Nutrition: Because of the weak absorption ability of its roots, a ginger plant requires good soil nutritional levels. According to Kun (1994), the fertilizer requirement

Table 6.2 Effect of pH on growth and yield of ginger

Rhizome weight

Treatment Plant ht (cm) Tillers/plant Leaves/plant (g/plant)

for producing 1,000 kg fresh ginger is N (nitrogen) — 6.34 kg, P2O5 (phosphorous) 0.75 kg, K2O (potassium) 9.27 kg, Ca (calcium) — 1.30 kg, and Mg (magnesium) 1.36 kg.

The mineral absorption varies in different stages of growth. Generally, ginger plants absorb little fertilizer in the seedling stage as it grows slowly and the biomass production is small. During the active growing stage, the absorption rate and quantity increase greatly with the increasing growth rate and biomass (Xianming, 1961). It has been measured that the absorption quantity of N, P, and K in seedlings is 12.25 percent of the total absorption in the whole growing period and 87.75 percent during the active growing stage (see Figure 6.6). During the whole growing period, value of absorption of elements follow the order K > N > Mg > Ca > P (Xu et al., 1993).

Figure 6.6 The absorption of some minerals by ginger.

Time (Day/Month)

Figure 6.6 The absorption of some minerals by ginger.

Ginger is sensitive to N, P, and K nutrition. N is the important component of protein and the major element of chlorophyll. So it is closely related to photosynthesis and many other primary and secondary metabolic processes (Kun and Feng, 1999). K is vital to the functioning of many enzymes. It influences many metabolic functions and has a great effect on growth, transportation of photosynthates, and respiratory metabolism, besides being an ingredient of many organic compounds of plants. P also participates in many metabolic functions including nucleic acid metabolism and is closely related to growth, yield, and the quality of crops (Xizhen et al., 1998b). So the quantity of N, P, and K fertilizer has a great effect on the growth and yield of ginger (Table 6.3) (Xizhen et al., 1997a, b).

Ginger needs a balanced fertilizer application. If some nutrient element is absent, the growth and development of plants will be affected and the composition of the rhizome will be affected too, leading to a reduction in carbohydrates, protein, and volatile oil. If excessive fertilizers are used, the roots will find it difficult to absorb the minerals because of a too high ionic concentration and a too low water potential of soil. As a result, the growth of aerial shoots will be suffocated, photosynthesis will be weakened, and the yield will be reduced (see Tables 6.4—6.6).

In addition to N, P, K, Ca, and Mg, some microelements are also necessary for the growth of ginger. Kun had shown that 3.67 g B (boron) and 9.88 g Zn (zinc) are absorbed per 100 kg rhizomes. Xiaoyun (1993, 1994) concluded that the yield will be increased

Table 6.3 Effect of N, P, and K on growth and yield of ginger

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