The objective of this research was to determine the water requirement of Alpinia purpurata (red ginger) to produce high quality inflorescences. A farm using overhead irrigation with impact sprinklers at 4.3 mm per hour for one hour three times per week proved superior to the drip irrigated three cultivars of Alpinia purpurata, red ginger, 'Eileen McDonald', and Ginoza No.__, were grown under different irrigation levels at the Waimanalo Research Station located in Waimanalo, Hawaii from August 1991 to May 1993. Five drip-irrigation treatments corresponded to replacement of 0.33 to 1.67 of pan evaporation.
Weekly samples of the shoots were monitored to determine the stages of growth and development of the plant. The stages of inflorescence development in chronological order were: inflorescence initiation, appearance of color at the shoot tip, swelling of the inflorescence, appearance of the inflorescence, and harvest of the shoot. The influence of water application rates was monitored by stomatal conductance, relative water content, total leaf area per shoot, inflorescence diameter and length, shoot diameter and length, number of expanded leaves, and number of inflorescences per clump. Seasonal trends were compared with environmental data collected by a weather station. The components of the soil water balance were determined.
The stages of inflorescence development were not affected by water application rates but were affected by the cultivars and seasonality. The average durations (weeks) for the appearance of color at the shoot tip, swelling of the inflorescence, appearance of the inflorescence, and harvest of the shoot were 20.8, 21.5, 23.2, and 26.4 respectively. The Ginoza cultivar took significantly longer from shoot emergence to all four stages compared to the other two cultivars. The Ginoza cultivar also produced the longest shoots, most number of expanded leaves, and shorter inflorescences than 'Eileen McDonald'. Shoots which emerged at the start of increasing temperatures and solar radiation (March and April) averaged shorter times to the four stages compared to shoots which emerged at the start of decreasing temperature and solar radiation (November).
The highest irrigation treatment produced higher quality inflorescences, but all treatments appeared to experience frequent water stress due to deep drainage
