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Rural Industries Research & Development Corporation
Nutrition and Irrigation Management of Rambutan for Maximisation of Yield and Quality
by Chris WicksAugust 2002
RIRDC Publication No 02/106 RIRDC Project No DNT-26A
The rambutan (Nephelium lappaceum L.) is a large tropical tree that is a member of the Sapindaceae family along with Longan and Lychee. The rambutan is believed to be native to West Malaysia and the islands of Western Indonesia and as such prefers a tropical climate (within 15 o of the equator) on land below about 500m elevation. The climate should be warm and wet with few dry periods. The soil should generally well drained and slightly to moderately acidic.
In Australia the fruit has grown in popularity and a considerable area has been planted to Rambutan.
The rambutan industry was valued at $2.7 M in 1995 with the bulk of the crop being grown in North Queensland. The Northern Territory industry although smaller provides approximately a third of the value of the industry. In the Northern Territory, rambutan is an emerging tropical fruit crop and is profitable to grow with a market value in 1994 of $800,000 with an estimated 12,000 trees planted (140-200 ha). The majority of this development has occurred without a rambutan growing culture or knowledge.
Irrigation is a necessary part of production in the wet-dry tropics. In the NT, the dry season (May to September) is the main period during which irrigation is required. Irrigation rates and frequency varies from orchard to orchard. The wet season (October to April) although reliable in terms of total rainfall, is still a period in which irrigation is required due to in-season variability.
Previous work has developed an irrigation management strategy for rambutan production in the Darwin region. This strategy includes a droughting period in an attempt to improve flowering.
Delayed or poor flowering and poor fruit retention is of major concern to growers in the NT, who are able to exploit a market window which exists in November - December, prior to the onset of fruit availability in Queensland. Better control of flowering and fruiting through improved irrigation management would greatly facilitate income stability for growers in the NT and Queensland.
Another area of poor knowledge was in respect to tree nutrition. Much of the literature on fertiliser management of rambutan is practical in nature with few clear scientifically based experiments.
Previous work conducted in the NT produced in 1997 the most comprehensive guidelines of rambutan fertiliser requirements to date. That study suggested that in commercially productive rambutan grown the NT, the chief demands are for nitrogen, potassium and phosphorous.
The previous work conducted in the NT while excellent was still very basic in comparison to other tree crops grown in Australia. There was still lack of information on fertiliser management, in particular the effect of frequency of application during fruit development. This is something best established in the field. Thus there is much to be gained by monitoring growers with differing practices.
The aim of this project is to improve our understanding of nutrient and irrigation management in rambutan, with particular emphasis on management through the fruit filling stage. This should lead to improved yield and fruit quality with more efficient use of fertiliser and irrigation inputs and hence increased profitability. The monitoring and reporting components of the project are closely linked with industry participation hence the uptake of new findings will hopefully be rapid and lead to improvements in productivity.
In 1998 a large proportion of the rambutan growers of the NT were requested to take part in this project. In total, 14 growers replied in the affirmative. These grower’s properties plus the Coastal Plains Horticulture Research Farm (CPHRF) (managed by the NT Department of Business, Industry and Resource Development) were all selected for the Nutrition portion of the project. A sub-group of 9 grower properties plus CPHRF were selected for the Irrigation portion of the project.
The field methodology for the Nutrition Trial consisted of sampling soil and leaf from each property four times per year. Thus there were thirteen separate samplings. The sampling times were set so that significant tree behaviour (flowering, flushing, etc.) could be represented. At each sampling a methodology developed by earlier workers was used to reduce variability both in the field and in the laboratory.
The results of the laboratory analyses was then combined with yield data and other measures of tree vigour to develop for each nutrient a suitable range for levels in leaf and soil. The methods used to develop these recommended ranges involved using a various techniques proven in other crops.
The best method for proofing the new ranges is through linkage to improved yield. Unfortunately this was very difficult to do for this project, as the three years the project covered were mainly poor years.
The 1998 season was very promising until a cyclone crossed near Darwin in early December, causing a very large fruit drop with estimates of crop loss ranging between 30 and 75%. While in 1999 and 2000 there were some cold and dry spells just on and after flowering that limited pollination and caused the abortion of young fruit.
However analysis of other measures of tree and soil health and balance indicate a large amount of general improvement. This improvement was achieved through group discussions and one-to-one sessions. The growers were keen to be involved and openly discussed management practices. There were over twenty meetings with the growers group throughout the time of the project, which is something of a record for such a small group.
This project also showed that there are no significant reasons that fertigation cannot be used instead of broadcast (of granular fertiliser) to provide rambutan with its nutrient requirements. However there was no clear advantage either, so any decision made can be more readily made using economic or time-restraint criteria rather than tree vigour or yield.
The significant impact of the environment on this project showed yet again that not enough is known about the influence of the environment (and especially a harsh environment such as is found in the NT) on flowering and fruiting of rambutan. More work needs to be done in this area.
With regards to Irrigation Management this project was more like an extension exercise than a strict scientific study. On each of the ten properties selected, three trees of the same variety, age and vigour were selected to be the representative trees. At each of these trees (that were not always the same trees as those sampled for soil and leaf nutrition) a range of soil moisture monitoring devices were installed.
Each property also had a water meter installed in a lateral irrigation line. There were also rain gauges and temperature and relative humidity loggers installed at most of the properties.
All ten properties were visited once per week and the soil moisture measured and each monitor tree was also visually assessed for gross phenological behaviour (Flushing, Mature/Resting, Flowering, Fruiting). The Tinytalk II loggers were downloaded fortnightly. At each property the latest soil water readings were related to the grower. Wherever possible, the grower accompanied the researcher during the data collection and was introduced to the mechanics and theory of measuring and interpreting soil water status.
In the main, most growers were quite good at managing the water inputs provided to their rambutan tree. An analysis of actual inputs versus recommended inputs indicated that once the rain had finished in mid-April the growers were all close to the recommended level. However the level of inputs was still significantly (p=0.01) different from recommended. Most of the difference occurred during the stressing period. In 2000 the flowering was later than normal which could explain the higher inputs, however it is those very years of poor flowering that stressing is meant to be most beneficial A further analysis of water inputs and soil water content showed that there were a number of growers that were either under or over irrigating to a large degree. What was exceptionally worrying is the very low levels seen during fruitset and filling when the trees are most sensitive to water stress. A large fruit drop occurs every year in the NT rambutan industry mainly due to the hot, dry climate encountered during fruitfilling but this poor irrigation management may be contributing to this problem.
However even this problem had an excellent result – through the training and example of this project, seven growers now own and operate a tensiometer system. That was one of the main reasons behind this entire water management exercise.
Any further work in these areas is best conducted by the growers themselves in consultation with the Horticultural Extension staff of the NT Department of Business, Industry and Resource Development.
The main findings of this project are: A new critical range for rambutan soil and leaf nutrition has been developed.
Growers have successfully taken up soil water monitoring principles and practice.
Further work is urgently required on the influence of the environment on rambutan flowering and fruit retention under NT conditions A final conclusion of this project is that cultivating an open air of discussion and discovery amongst the growers was an excellent method of developing new strategies and facilitating the uptake of new technologies
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