Abstract:
Protected cultivation offers several advantages for high-value crops such as salad
cucumber by providing a better-controlled environment, reducing pest and disease
pressure, and enabling year-round production. One of the main factors affecting
yield attributes in controlled environmental cultivation is the structural design
of the polytunnel. An experiment was conducted to evaluate the effectiveness of
two polytunnel designs using salad cucumber (Cucumis sativus L. var. Hanyan
CU-13502) as the test crop. The experiment compared two polytunnel designs:
an improved, naturally ventilated Design (T1) and a conventional design (T2).
Data on cucumber growth and yield, tunnel temperature and relative humidity,
disease incidence, and cost-benefit analysis were collected. Growth and yield parameters
were recorded from thirty replicates per treatment for 90 days from seed
germination. Under identical management conditions, T1 demonstrated superior
vegetative growth with a significantly higher number of leaves per vine and
greater above- and below-ground dry biomass compared to T2. However, time to
flowering, vine length, number of fruits per vine, fresh fruit weight, and total fruit
yield per vine did not differ significantly between tunnels. Despite similar yield
quantities, T1 produced a higher proportion of internationally marketable fruits
(dark green fruits without defects and diameter 4.0–3.5 cm), indicating superior
fruit quality. Disease incidence was significantly higher in T2, with 70% greater
prevalence of downy mildew and powdery mildew, which could be associated with
elevated temperatures hence reduced incubation period. Mid-day tunnel temperatures
were higher in T2 compared to T1, while relative humidity did not differ
significantly. Economic analysis indicated a benefit-to-cost ratio of 1.82 for T1
and 1.63 for T2, with the difference mainly attributable to construction costs.
Based on the results of the present study, the improved polytunnel design with
effective natural ventilation is recommended for adoption in the warm and humid
tropical areas of Sri Lanka to achieve superior product quality and reduced fungal
disease incidence in salad cucumber cultivation.
