Univanich Palm Oil Public Co. Ltd., 258 Aoluk-Laemsak Road, P.O. Box 8–9, Aoluk, Krabi 81110, Thailand.
*E-mail: john.clendon@univanich.com
1Highlands, New Road, Great Barford, Bedford MK44 3LQ, England.
The climate in Southern Thailand has a regular dry season, with 3 to 4 months of soil water deficit, and Univanich started commercial irrigation of oil palms in the late 1980s, installing over 600 ha of furrow irrigation. Research on irrigation commenced at the same time, and trials have compared irrigation methods, quantities of water applied, and interactions with fertilisers; the responses of different breeding materials are also being investigated.
A comparison of four irrigation methods (sprinkler, microsprayer, furrow and drip) showed no significant differences in yield responses, though there was a suggestion that drip might be superior to the other methods, and drip was also preferred on grounds of operating costs and ease of management. Some practical aspects of drip installation are discussed in the paper. At standard fertiliser rates, the response to irrigation levelled off at approximately 3mm rainfall equivalent (225 l/palm.day), averaging about 5.6 t FFB/ha.yr. There were significant irrigation x fertiliser interactions, and with increased fertiliser inputs, the response to irrigation was more or less linear, reaching 10 t FFB/ha.yr at 6.4mm rainfall equivalent (450 l/palm.day). Fertigation did not appear to give any advantage compared to manual fertiliser application. Irrigation scheduling was based on a calculated water deficit (rainfall minus pan evaporation); this was simpler than using porometer or tensiometer measurements. The yield response to irrigation depended on the severity of the dry season. The response in any one year was related to the water deficit in the first quarter of the year, and also to that two years earlier; a multiple regression explained 91% of the year-to-year variation in yield response.
As part of the Univanich breeding programme, several progeny trials have been duplicated with and without irrigation. In the first of these trials, some progenies appeared to be more sensitive to drought, and gave larger responses to irrigation, than others. This could give breeders the option of selecting drought tolerant material for planting in areas where irrigation is not possible, or irrigation-responsive material for sites where irrigation is intended.
