Australian tropical fruit orchards are traditionally grown on flat or slightly undulating land. This is primarily because of the costs of harvesting and tree management – a large expense given our high labour costs. In Thailand however, their good flat agricultural land is used for rice and vegetable production and the hillsides are reserved for fruit tree orchards. Obviously the low labour costs make this possible. Khun Pradoldej Kalayanamit, the largest lychee grower in Thailand with 8 lychee orchards, is also a mango, tangerine and strawberry grower. He told me he pays his workers 75 baht a day (about A$3.10) for a dawn to dusk workday and has about 10 full time workers per farm. The all year round jobs such as slashing, spraying, watering and pruning are all then done by hand at little expense to the grower.
I observed several methods of watering in Thai orchards. Several lychee farms, as well as some mango and longan orchards I inspected, dug a shallow pit around each tree on the drip line, which was then filled with water by buckets. Other orchardists in the Thaton / Fang area whose trees are often grown on 50 degree slopes, pump water to the top of the slope and simply let the water run down the hill. Many of the more affluent orchardists used under tree irrigation, but used tall aluminium stand pipes (2 – 3 m) to spray high up in the tree. They claimed this spread the water further and also added humidity to the air at the important ripening time, when fruit can dehydrate quickly, if not watered sufficiently. All farmers watered regularly but in small volumes. While most agreed to my way of thinking that water application was most important during early fruit set when cell division and development were taking place and again on colouring of the fruit, few seemed to use practices to take this into account. The bucket brigade watered “when the soil dried out” and I had little faith in flooding from the top of the hill. However the farmers with a regulated and controlled system (under tree irrigation) most often explained they watered for one hour every three days. Couple this with an 80 litre per hour microjet, and each tree only got about 200 litres per week! I regularly give my trees between 750 – 1000 litres per week, but in one single application, increasing this to 1500 litres per week during the rapid fruit enlargement just prior to harvest. Tests carried out in Australia several years ago indicated that water stress on bearing lychee trees had little bearing until the last 4 weeks before harvest, when fruit failed to develop to any size, and a lot of fruit was dropped by the stressed tree. As this does not seem to be a common problem to the Thai growers, there must be some other factors at work in Thai orchards. Further investigation is warranted on this apparent inconsistency.
As is the case in Australian orchards, fertilising of lychee trees was dependent very much on the soil types on which the trees were growing and the weather and rainfall statistics for the area. To grow trees successfully, free draining and not overly rich soils were needed, so that the supply of water and nutrients could be more or less controlled, especially in the all important pre-flowering time. All Thai farmers used a complete N-P-K fertiliser, with the most common one observed being a 15-15-15 mix. Application time was late March – early April when fruit was at pea size, with the rate being 1 kg per metre of tree height. Most farmers also used a foliar spray once a week for 3 weeks before panicle emergence. These rates were increased significantly for the few growers with orchards on the flat land, especially if they were on river flats.
While the use of fertigation is becoming increasingly popular in Australian orchards, I only saw one instance of this practice in Thailand. This was at the huge Boonrawd orchard near Chiang Rai in Northern Thailand. Owned by a major brewery in Thailand, money was not a limiting factor, so that recently sourced overseas technology was rapidly integrated into the whole farming enterprise. Here a 10-52-17 mix at 2500 parts per million was applied in two applications totalling 3kg. The first application was made just before the rainy season and the second during the rain. It was interesting to note the poor crop on these trees, which the owners attributed to the adverse weather conditions. My own experience however, would suggest that applying fertiliser both before and during periods of heavy rain would be counter productive, with the fertiliser being washed away or carried so far down into the sub-soils as to be unavailable to the shallow rooted lychee trees.
In summary then, Thai farmers operated under a similar belief to Australian growers, that is you fertilise to produce bigger and better fruit, rather than bigger trees. Fertilising both before and after fruit set is now widely practised in both countries, in the expectation that after harvest when trees are nearly drained in regard to available nutrients, the wet weather will result in only one or at the most two post harvest flushes, so that trees are kept smaller and in a fruiting rather than flushing state.
The use of organic fertilisers, though only practised by a small number of farmers at present, is, according to one grower I spoke to in Lamphun in Chiang Mai province, increasing rapidly. He uses a system called EM (essential micro-organisms) that he buys in from Japan. The make up of this liquid is kept secret by the Japanese, but is claimed to be a mix of soil health promoting organisms that replace the need for any fertiliser application. This product is mixed in to rice husks, animal manure and whatever other biodegradable product is available, has molasses poured over it and is then left for three days covered with hessian bags. There was obviously some reaction taking place, as this mixture was very warm to the touch, even though it was in the shade of a large shed. This is then used as fertiliser at the rate of 10kg per tree 3 times a year. Neem oil mixed with the EM is also used as an insecticide whenever necessary. The farmer claimed he produced the biggest and best fruit in his area and was rapidly convincing more and more of his fellow growers to switch to his methods. Unfortunately I could not see any of his fruit because he had already completed his harvest and neither could I see his trees as his paddock was too wet! Perhaps some follow up visits may be appropriate when I am next in that area.
In Australia at present, getting trees to flower regularly and heavily takes up most discussion whenever lychee growers get together. This is especially a problem on the hotter and wetter coastal regions, rather than on the cooler Tablelands region where I grow these delicious fruit. Flower induction is brought about by a combination of two factors – the point of growth of the tree and the weather. The first of these we can try to control, the second we cannot. The ultimate is to have your trees just starting a new growth cycle as the cold weather starts. This means having buds around the 1-3 mm size with the arrival of cold weather (< 15 degrees C) during the night, and in the low 20’s during the day. Buds bigger than 3mm will result in either all new growth or a mixture of leaf and flower and if the trees are not in a growth cycle and are dormant, they will likely stay dormant until the warmer weather arrives again and then be vegetative. Farmers in Thailand have similar problems and have developed several methods to ensure they have good flowering at least 9 years out of 10. These are cincturing, the use of potassium phosphate and the use of potassium chlorate, calcium chlorate or sodium chlorate. This method requires further investigation in the warmer growing areas of Queensland where flowering can often be irregular. Initial attempts at this practice have proved unsuccessful in Queensland in the one large scale trial that was conducted. However on talking to the grower involved in this, I believe the timing, so critical in this exercise, was not correct. While not being necessary on my own farm where I can more easily control growth, such a process needs to be revisited on coastal orchards in Northern and Southern Queensland. Already several growers in these areas to whom I have spoken, or who saw the process themselves when I took a group of growers to Thailand in May, 1999, have decided to put the process into practise on small areas of their own orchards for evaluation.
Depending on tree vigour and water availability, lychee trees can continue growth cycles well after the desired one or two flushes following the post harvest wet season. This dramatically increases the chances of trees being in a growth or hardening off stage with the onset of colder weather, resulting in little or no flowering. This was a particularly bad problem in the Chiang Rai province of Thailand.
Cincturing and Potassium Phosphate
This is a method also practised in Vietnam and China, where trees are ‘ringbarked’ to stop all vegetative growth. Each tree in an orchard has a narrow cut made around each branch after the tree has divided into the 4 – 6 branch stage. This cut must be very precise as far as depth is concerned, because if it is too shallow nothing is achieved and too deep and the branch dies. This is why individual branches and not the whole trunk is cinctured – better to lose one branch rather than the whole tree. The cut must go down to the cambium layer and no deeper. This has the effect of stopping the trees growth, with all its energy put into repairing the damaged section. Once this repair has been made, the tree switches back into a growth cycle. The Thai farmers, with assistance from their agricultural advisers, have found that if they cincture their trees in October each year, the exact date depending on their area, the trees will take around two months to repair themselves and then start a new growth cycle just in time for the new Thai winter, so that flower initiation occurs in January. Chiang Rai Horticultural Research Station set out to find an easy solution for growers of large orchards where cincturing was not realistic.
Researchers there have found the use of the chemical potassium phosphate goes a long way to solving this problem. The chemical is applied through a misting machine at 5000 parts per million at 7 day intervals for 2 or 3 times, about 6 weeks before anticipated cold weather (and flowering). This has the effect of hardening off any flush on the trees in only 2 or 3 weeks, much shorter than the normal 5 – 6 weeks and putting the trees into a dormancy stage – exactly what you want. Then with careful manipulation of water, you can induce flowering at the right time. A fellow lychee grower in Sarina has already put this process into effect on his own property, because when he arrived home from Thailand with me, he found his trees covered in a brilliant flush. He immediately applied potassium phosphate, the flush hardened off quickly and his trees are now flowering well. The process seems to work well and further research is needed into its causes and long term effects. Growers now have some hope of generating flowering on trees that are overly vigorous at the wrong times in the year, trees, which dutifully flowered 6 weeks later, and then set fruit. I ate about 2 dozen of these fruit when I visited his home (he would not let me eat too many, because they were making him a fortune, being out of season) and we then inspected his nearby orchards where the chemical had been applied at the usual time. These trees were covered in the most beautiful flowering you could imagine and he was expecting a crop of around 50 tonnes (A$165 000). All the longan orchards in Thailand used this chemical, although no one else mentioned the out of season application to induce flowering.
Opinions varied as to the best way to apply the chemical, with most farmers preferring the ground application method. One farmer I visited in Chiang Mai province physically raked all the litter and mulch out from beneath his trees before applying the potassium chlorate. He did this to aid absorption of the chemical into the ground. The litter was then raked back into place. However the results seemed to be worth the trouble. His 1000 five year old trees had a magnificent crop of fruit, which he estimated at 75 tonne, worth A$250 000. In Chiang Mai I had the privilege of having dinner and a long discussion with two Thai horticultural advisers. They were private consultants working mainly in Cambodia, who informed me that both calcium and sodium chlorate were both just as effective as potassium chlorate in this process, but claimed foliar application was more effective than ground application. Their recommended spraying rate was 50g per metre of canopy (ie a 3m tree requires 150g), six weeks before expected flowering. This matched exactly the rates given by the Chiang Mai farmer discussed above, who claimed to use 150g per tree on his trees of 3 to 4 metres. (They also showed me pictures of high density apple orchards in Cambodia with 36 000 trees per acre. They were harvested like sugar cane and simply left to reshoot from the stump). The use of these chemicals in promoting flowering in lychees is now just starting to be investigated in Thailand. One large grower in Thaton tried it for the first time this past year and did not notice any appreciable difference in these trees compared to his others, as they all flowered well anyway. This year he is going to apply the chemical earlier to see if he can induce an early flowering and has promised to keep me informed of the results. Should such a process be as successful in lychee as it appears to be in longan, the potential for further development would be enormous.
This process has been occupying the thoughts of Australian growers for several years now, as the Canopy Management Research team, with funds from the Australian Lychee Growers (ALGA) and the Horticultural Industry Research Development Council (HIRDC) have looked for ways to control canopy size in lychee trees, while maintaining production. For this reason, I was particularly interested to see how growers in Thailand pruned their trees to keep them manageable. The major point I gained from many growers with whom I spoke about this was prune immediately after harvest and heavily. This was best illustrated with a visit to a small orchard at Mae Sai in the Golden Triangle area. His pruning theory was to remove all upwardly growing branches immediately after harvest, leaving his trees in a hollow mushroom shape. The trees then flush heavily for 2 flushes, at which time they are cinctured to prevent further flushes. He claimed figures of 200kg per tree on a regular basis, however I visited his orchard just after harvest and could not see this for myself. I did see his pruning taking place and may attempt his method on some of my larger trees in the near future. Other growers pruned the top out of their trees one year and the sides the next, claiming this was less stressful on the trees than a full prune each year. From what I have seen both overseas and in Australia, I would suggest that pruning, whether it be light or heavy, doesn’t really matter as long as it is done straight after harvest and the trees are encouraged to flush heavily after that. The trick is to manage to stop them in time to provide a period of dormancy before flowering should commence.
Harvesting, Transporting and Processing the Fruit
While some similarities were evident in the Thai harvesting exercise, there were a great many differences. Thai farmers only picked from sunrise to around 10am, but whether this was to promote shelf life as is the case in Australia, or to meet deadlines for transport was not explained. Once in the packing shed the differences were considerable. The Thais use no machinery – all work is done by hand, mostly using imported Burmese people at around A$2 a day. The fruit panicles are roughly graded and split or damaged fruit removed. The fruit is packed still on the panicle into 10 kg boxes, but not refrigerated. The whole process must be completed before 12:30pm, when the fruit is loaded onto a truck to be taken to the nearby depot, where it is loaded aboard a larger truck that leaves for Bangkok at 1:00pm. Here it arrives at the markets in the early hours of the morning, where it is sold that day. There is no need for refrigeration facilities due to the rapid turnover of the fruit. Thai people adore lychee – they are no sooner on the shop shelves than they are walking out the door, so that new stock is required each day in large quantities.
Thai supermarkets also have a very low mark up on local fruits, so that they may compete with the hundreds of street vendors also selling fruit. This of course helps to ensure rapid turnover and fresh product each day. A visit to Talad Thai, the newest and largest Fruit and Vegetable Market in Bangkok, confirmed this. Despite the huge range of fruits available, it seemed every buyer there made sure they had lychee on their list. At 250 baht per 10kg box (farmers were getting between 17 and 19 baht per kilo) the fruit was very inexpensive by Australian standards, but the supermarkets were still retailing them at only 30 to 35 baht per kilo.
Fruit rejected at the farms as not suitable for fresh sale is sent to one of several canneries in the lychee growing areas. On a visit to such a cannery on the outskirts of Chiang Rai, I witnessed this lower grade fruit being processed into canned fruit, boiled down into syrup for the canned product or processed into juice. Nothing was wasted. The wage structures in Australia would preclude such an operation on a seasonal fruit being set up here. Instead our reject fruit is dumped on the ground to rot and be used as mulch – one of the prices we pay for growing a seasonal crop in a rich industrialised country