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Rural Industries Research & Development Corporation
Longan Improving Yield and Quality
by Yan DiczbalisNovember 2002
RIRDC Publication No 02/135 RIRDC Project No DAQ-251A (Longan)
The longan (Dimocarpus longan Lour) is a tropical fruit and member of the Sapindaceae family closely related to the lychee and rambutan. The longan tree can grow to 10 m in height and up to 14 m in width.
The origin of longan is still disputed with some authors limiting the area of origin to the mountain chain from Burma to southern China while others extend it to south west India and Sri Lanka (Wong and Ketsa, 1991). It is commonly grown in Thailand, Cambodia, Laos, Vietnam and Taiwan where it is a major commercial crop with strong intra and inter country demand. Hong Kong and Singapore are major outlets for longans. Trees were imported into Florida in the early 1900’s (Morton, 1987) and from there into Hawaii where it is grown commercially for export to mainland USA.
Emigrants of Chinese origin, in the late 1800’s or early 1900’s, most likely brought longans into Australia. Commercial plantings commenced in the 1970’s (Menzel and McConchie 1998). Twenty varieties have been imported into Australia and have undergone preliminary evaluation in the Atherton Tablelands region, west of Cairns (Winston and O’Farrell 1989). The longan industry in Australia with 34,000 trees in 1997 is distributed from northern New South Wales to Cape Tribulation in north Queensland (Anon 1998). Current plantings are reported to be in the vicinity of 45,000 trees and the annual production of 300-500 tonnes is valued at $2.0M (Neil Sing pers. Com. 2002). The main commercial varieties in Australia include, Kohala and Homestead (USA selections) Biew Kiew, Chompoo, Dang and Haew (Thai selections) (Anon 1998).
The Australian longan and rambutan industries, together with DPI, NT DPIF and RIRDC and other bodies have, over the last few years engaged in detailed assessments of industry research and development needs. Industry strategic plans have been developed for the longan industry (Anon 1998) and a commitment to support research has been made by the relevant organizations. The longan industry has identified nutrition and irrigation research as a priority issue.
The project aims were to monitor changes in longan leaf and soil nutrient status over three seasons, measure grower fertiliser inputs in relation to the above, assess the effect of nutrient status on productivity, monitor tree phenology in relation to climate and irrigation management and quantify longan water/irrigation requirements.
This report details the findings of three years of study from July 1998 to May 2001. Through this project longan researchers, extension officers, growers and associated industry organizations are able to access an improved understanding of the effect of nutrition on yield. Tentative leaf and soil standards were developed to use as a guide to fertiliser management.
The project was unable to identify any direct links between tree nutritional status, fertiliser inputs and yield. Its important to note that all commercial orchards surveyed had relatively high leaf nutrient status and no unfertilised trees were included in the study. This suggests that within the range of nutrient status observed other factors such as pruning practices and climate play a more important role in flowering and subsequent yield. Despite the lack of relationship between nutrient status and yield, the survey indicated that high leaf N levels (N 2.0%) during the period leading up to flowering should be avoided because it may be detrimental to flowering and hence subsequent cropping.
A guide to fertiliser requirements was developed using a nutrient budget approach where nutrient inputs are based on fruit production and removal and take into account additional nutrient loss via leaching, runoff and fixation.
As a result of the development of a nutrient budget, inputs can now be geared to production rather than based on an ad hoc approach. This allows for potential savings on fertiliser inputs, however, more importantly the nutrient budget approach has the potential to reduce fertiliser loss and hence contamination of ground waters.
Longan irrigation requirements during fruit filling were monitored at three sites and the crop factor (tree water requirements relative to evaporation) estimated as 0.83. Hence irrigation requirements can be calculated using a simple evaporation based calculation; Irrigation Requirements = canopy area (m 2 ) * Evaporation Rate (mm/week) * Crop Factor Growers are advised to monitor the above irrigation recommendations with readily available soil moisture sensing technology and where possible the addition of a water meter. These simple tools allow the orchard manager to fine tune irrigation inputs to their crop, season and soil type and minimize off-site effects.
As an outcome of the project longan growers should be encouraged to monitor fertiliser inputs in conjunction with regular leaf and soil analysis and yield records. In this way fertiliser inputs can be geared more closely to nutrient outputs. The following key points should be included in a monitoring system; Develop fertiliser input worksheets that can be easily transferred to spread sheet software packages.
Use of the tentative leaf and soil standards as a guide to current fertiliser management strategy.
Develop a fertiliser management spreadsheet based on nutrient removal through fruit and other loss factors and encourage its use among industry members.
Use the nutrient budget to develop a fertiliser program for the season, based on yield projections.
Recommend the use of fertigation to improve the efficiency of fertiliser application and use.
Gear fertiliser inputs to periods of maximum fertiliser demand (fruit filling).
Monitor longan yields in conjunction with fertiliser management records to validate the nutrient budget approach over a minimum of 5 seasons, to reduce the effects of climate and other management issues (eg. pruning) on yield.
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