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Irrigation
Maintenance of optimum soil moisture is essential for plant growth, yield and qual-
ity of fruits. Once a plant is properly established, it grows continuously during winter
months. It sets flower and fruit at every leaf axil that is produced. In general, 1.0 m^2
of leaves transpires 1.0 L H 2 O daily, but can rise substantially with increasing evapo-
rative demands. A papaya plant with 35 leaves, equivalent to approximately 3.5–
4.0 m^2 leaf area, can fix ca. 70 g of CO 2 and transpire ca. 10 L of water daily (Ming
and Moore 2014). For well-watered papaya plants, the crop irrigation coefficient (Kc)
is close to unity but may reach values of 1.2, as a result of the strong dependence
of canopy gas exchange, photosynthesis, water use and the solar radiation available
(Campostrini and Glenn 2007).
Yield is obviously related to the number of leaves produced and the amount
of growth added. Hence, water is required during the growing period for poten-
tial yield. Under low moisture conditions, floral sex shifts towards female steril-
ity resulting in low productivity (Ram et al. 1985a, b). Responses to water stress
include dehydration postponement through strict stomatal regulation, cavitation
repair and intense osmotic adjustment (Mahouachi et al. 2006). At the same time,
over-irrigation may cause root rot diseases. Thus, efficient water management is
required. Number of irrigations depends upon soil type and weather conditions
of the region. Protective irrigation is required in the first year of planting (Figure
7.1a). In general, irrigation to grown-up plants is given once in 7–10 days in winter
and 4–5 days in summer. In the second year, when the plants are ladden with fruits,
irrigation at fortnightly interval in winter and at 10 days interval in summer is
needed from October to May. Excessive moisture is more detrimental to plant than
moisture stress necessitating the effective drainage system, especially in heavy
soils under high rainfall conditions, to avoid plant mortality. Studies conducted
at Coimbatore have also indicated that papaya has high tolerance for heat and
soil moisture for higher productivity; however, moisture stress at fruit develop-
ment stage should be avoided. Total water requirement of CO-2 papaya under trop-
ics is estimated to be 1800–1900 mm and excessive depletion of moisture causes
reduced growth and yield. However, intermittent moisture stress induces deep root
penetration. Depletion of soil moisture also causes increase in N and Mg content,
while Ca content is reduced. Irrigation at 60% available soil moisture depletion is
found to be the optimum for papaya. Regular irrigation is an important aspect in
papaya cultivation, which helps in the growth, fruit development and high yield.
Moisture stress inhibits the growth and also promotes male floral characters. The
ring system of irrigation has been found very effective among different methods.
This system helps in preventing the collar rot (Figure 7.1b) as there is no direct
contact between the water and the stem portion. In low rainfall areas, where water
is scarce, sprinkler or drip systems of irrigation can be adopted for higher produc-
tion, saving water from 50 to 60%.