Ubi Farming

True yams (Dioscorea spp., Dioscoreaceae) are the third most important tropical "root" crop after cassava (Manihot esculenta, Euphorbiaceae) and sweet potato (Ipomoea batatas, Convolvulaceae).

They are climbing perennial vines with shiny, heart-shaped leaves, arising from large underground stems that are technically called tubers rather than roots. Like a potato, the tubers can be propagated by planting sections containing the "eyes" or buds; however, harvesting them is a laborious task because the tubers are deeply buried.

Ubi (Dioscorea alata L.) or yam is a vine which produces both aerial tubers called bulbils and underground tubers or roots. The bulbils weighing a few grams and to over a kilogram come out from the leaf axils three (3) months after planting. The underground tubers weighing one to six kilograms can be harvested six months after planting.

The ubi roots has 70 percent moisture and 28 percent starch. It also contains traces of fats, crude protein, sugar, crude fiber, ash and Vitamin C, B1 and B2.

Ubi is grown primarily for its roots or tubers. The tubers can be eaten boiled, baked, roasted, flakes, chips and can be processed into powder form. Dehydrated yam slices are used for the preparation of food such as ice cream, cakes, pastries and other dessert. The ubi skin or peeling can be used as a raw material for the manufacture of food coloring.

Recommended Varieties

1. VU-1 (BASCO UBI)
Yield : 18-20 tons/ha
Dry Matter : 28.80%
Starch : 21.25% (wet basis)
Protein : 1.55% (wet basis)
Maturity : 29 weeks
Skin color : brown
Cortex color : white with purplish flesh/tinge
Growth habit : green with purplish leaf veins, nodes and petiole ends

2. VU-2 (ZAMBALES UBI)-LA 167
Yield : 16.08 tons/ha
Dry Matter : 30.49%
Protein : 1.33%
Maturity : 29 weeks
Skin color : brown
Cortex color : purple
Growth habit : twinning
Foliage color : green with purplish leaf veins, nodes and petiole ends
Reaction to disease : Resistant to foliar fungal disease

3. VU-3 (LEYTE)-LA 100
Yield : 21.26 tons/ha
Dry Matter : 30.10%
Starch 20.96%
Protein : 1.52%
Maturity : 31 weeks
Skin color : brown with blackish tinge
Cortex color : cream to pink
Flesh color : white
Growth habit : twinning
Foliage color : green with light green veins, petiole ends

4. KINAMPAY VARIETY
Kinampay Variety is known for its sweet aroma and good taste and dubbed as the "Queen of Philippine Yams" which has smooth and round roots. Ubing Kinampay is classified into five (5) varieties namely;

Original Kinampay : reddish purple flesh
Kabus-ok : white flesh with large roots
Tamisan : reddish white flesh and sweeter in taste
Binanag : creamy-white flesh and elongated
Binato : big and hard root with whitish flesh color

Other local cultivars are Binalog, Ubsah, Appari, Negro, Alabat, Kameral I and Kameral II.

Soil and Climatic Requirement

Ubi thrives anywhere in the Philippines and in a wide range of soil types and elevation because it can tolerate adverse conditions such as droughts and pest infestations. However, it thrives best in sandy loam or silt loam fertile, well-drained soil and temperature ranging from 25°C to 30°C. Ubi needs ample moisture throughout the growing season.

The crop can be grown anytime of the year but for best results, planting should be done at the beginning or just after the rainy season when it can obtain all the moisture it needs for growth.

Cultural Management

Land Preparation

Tillage - Two plowings and two harrowings are usually enough for ubi for a field that has been previously cultivated. Plow deeply. Ubi needs a deep loose soil. Harrow along and across the length of the field to pulverize the soil.

Seedbed - Plant ubi on flat or ridged seedbeds. These are preferable to other types of seedbeds;

If flat beds are used, plant after the last harrowing.

On sloping or rolling fields, contour the ridges to minimize soil erosion.

Crop Establishment

Setts Preparation

About 20,000 to 27,778 setts are needed for a hectare of land. There are four types of setts: head, middle, tail and whole. The first three are prepared by cutting large tubers into pieces. The fourth type refers to the whole small tuber. Setts should be obtained from healthy tubers of healthy plants.

Slice large tubers into setts weighing from 60g to 250g. Do not slice tubers weighing less than 60g. Be sure that each setts has enough skin area. Treat cut sides of setts with ash or fungicide. Air or sun-dry the setts until cuts are dry. After drying, setts maybe pre-sprouted or planted directly.

Pre-sprouting Setts

Sprouts emerge from setts about 2-3 weeks after planting. Pre-sprouting the setts before planting is recommended to minimize weeding expenses before sprout emergence.

For a pre-sprouting bed, dig a shallow ditch in a shady area or clear the ground in a shady area by removing stones, weeds and debris.

Plant setts cut from large tubers either skin up or skin sideways. Whole tubers measuring 60 to 250g either crown up or crown side ways should be planted. Then cover the setts with a thin layer of soil. Water the pre-sprouting bed at least one a week until most of the setts have sprouted.

Preparing Pre-sprouted Setts for Planting

With pre-sprouted setts, planting may either be staggered or done at one time.
Staggered Planting

The following activities must be performed in all batches of planting:

1. Remove from pre-sprouting bed setts that have emerged to prevent sprouts from growing too long.
2. Place the sprouted setts on a platform in a shady area.
3. Repeat the process every week or every two weeks until the desired number of sprouted setts for one batch of planting is obtained. Plant before the sprouts become too long to transport or before sprouts start wilting.

One-time Planting

The procedure of sett preparation is essentially the same as that fro staggered planting. One-time planting is done only after most of the viable setts have produced sprouts. At this time, sprouts of some setts are already very long. Cut along sprouts before transporting setts to the field for planting.

Planting

Planting is done from March to June. However, planting time for ubi depends upon the time tuber dormancy is broken and the start of rain in the area.

1. Non-sprouted Setts

Plant setts in the seedbed at a distance of 1m x 50cm or 60cm x 60cm. Plant the setts 10cm deep during the rainy season and 15cm during dry season, especially if the field will not be mulched. Setts can be planted in any position

2. Pre-sprouted Setts

Plant the setts at the start of rain if it is not possible to irrigate or mulch the field. Plant the setts in the seedbed at a depth of 10cm and a distance of 1m x 50cm or 60cm x 60cm. Be sure to orient the sprout upward in planting.

Divide the field into four to six section and if staggered planting is applied. Each section is intended for one planting batch. The size and the time to prepare each section depend upon the rate of sett sprouting.

Mulching

Mulch the field to reduce soil temperature, conserve soil moisture, increase organic matter content of the soil and suppress weed growth.

Use dry coconut fronds, corn stalks, rice straw and other similar materials in mulching. See to it that these materials are free from weed seeds.

Mulch the field just after planting. Make the mulch thick if rice straw or any material that rot easily are used.

Weeding

With non-sprouted setts and without mulching, 3-5 weedings are needed. With pre-sprouted setts and with mulching, only two weedings at 2-month intervals are needed.

While plants are still short and unstaked or if the stake set-up allows, use animal- drawn implements to control weeds in an unmulched fields. Vines crossing the path of the animal should be lifted and placed along the rows before plowing.

Use handtools to weed the field once plants are already staked and the stake set-up does not allow the use of animal-drawn implement or if the field is mulched.

With non-presprouted setts and without mulching pre-emergence herbicides applied within one week after planting, maybe used to control weeds.

Staking

Place a stake for each plant before vines start crawling on the ground. Stakes should be 1-2m long. Bamboo, wood, cassava stalks, talahib stalks, or any similar materials that can support the ubi vines which can be used as stakes for at least seven months. If cassava stalk is used, it should be set up in an inverted position (young end down) to prevent the stalk from producing new shoots.

Training Vines

Ubi vines twines to the right. When vines start trailing on the ground, train the vines climb their respective stakes. Also, train the vines again when branches start crossing the rows, especially when weeding and hilling-up operations by using animal-drawn implements.

Nutrient Management

A hectare of ubi can remove about 128 kg nitrogen, 17kg phosphorus and 162 kg potassium from the soil. Collect soil samples from the field first before applying fertilizer and submit for soil analysis to the Bureau of Soils and Water Management.

1. Inorganic Fertilization - The recommended amount of fertilizer should be split into two, one half to be applied about one month after emergence (or one month after planting of pre-sprouted setts) and the other half about 2 months after the first application. Apply the fertilizer following the band method and placing the fertilizer about 10 cm away from the plants.


2. Organic Fertilization - Use of compost which is a mixture of decayed organic matter from plant parts and animal manure. Mix the compost with the soil during land preparation or place the compost just below the setts during the planting.

Harvest Management

Ubi is ready for harvest when its foliage is already yellowing or drying up. For most varieties, the drying up period of the foliage starts in late November and lasts until January the following year. Tubers intended for sett production should be harvested at the later part of the drying up period. However, tubers for consumption or for selling in the market should be harvested earlier, even before foliages dries up.

Harvesting ubi in sandy soil, use sturdy sticks sharpened at one end to dig out the tuber, remove soil particles that cling to the tuber and cut the vine at the base. For clayey and varieties with deeply buried tubers, use ubi harvester developed by the Philippine Rootcrops Research Training Center.

Prior to transporting, separate healthy tubers from diseased ones. Tubers should be arranged in a container in such a way that rubbing of tubers inside the container can be prevented. Place tubers in rattan baskets or in bamboo or wooden crates lined with soft material such as paper, banana leaves or straw. Arrange 2-4 layers of tubers in the container, the bigger the tubers the fewer the number of layers. Place soft material between layers and between tubers in a layer to serve as cushion.

Storage

Tubers need to be stored in a bam while they are not yet marketed nor consumed whereas tubers intended for setts need to be stored until planting or replanting time. Storage structure for ubi should be shaded and adequately ventilated. There are three methods of storage:

1. Barn storage - tubers are tied to vertically arranged poles held together by sturdy horizontal poles. Durable tying materials like rope are use din tying the tubers to the poles. The vertical poles are arranged about 50cm apart.
2. Platform storage - large tubers are placed in one layer on raised platforms constructed in the shed. Small tubers are arranged in 2-3 layers.
3. Shelf Storage - Tubers are placed on several decks of platforms instead of just one deck.


References: Agriculture and Fisheries Information Service-Department of Agriculture, Elliptical Road, Diliman, Quezon City 1100, April 2004; photo courtesy of www.aracaria.com.au

Rubber Farming and Production

Rubber is a material having varied industrial, technological and domestic uses. It has high export potentials and is rated as one of the most profitable agri-industrial ventures in the country.' The prospects of the natural rubber industry in the Philippines can be gauged by the domestic and export market requirements, Despite the threat of synthetic rubber, the market for natural rubber still remains healthy and attractive due to an ever increasing demand for rubber products. Added to this , is the unique technical properties of natural rubber making @ suitable for varied purposes and well favored compared to synthetic rubber. Therefore, the natural rubber industry will continue to be of greater importance.

CLIMATE, SOIL AND CLONE SELECTION

In general, rubber is grown within the geographical zones lying 10 degrees to 15 degrees on ether side of the equator. Warm humid climate with temperatures ranging from 20 to 35 degrees centigrade is required and an annual rainfall pattern that is fairly distributed and without morning rains is best needed by the crop.

Rubber is suitable in a wide range of soil types provided that drainage, soil reaction and soil depth are not limiting. Slightly rolling lands with deep surface soil are ideal for rubber growing. Rubber can be planted in steep slopes provided that contour planting is observed. Well-drained flat or level lands maybe good also for rubber. Soils planted to rubber in the Philippines is moderately to slightly acidic (pH ranging from 4.5 to 6.5) on the standard scale.

Clone selection should be given importance in order to have a successful rubber plantation. Optimum yields cannot be attained even with a favorable environment I the clone used is not of high yielding variety.

In most plantations, RRIM 600 occupies at least 70% of the area. The remaining 30% is planted to any of the following: PB 330, RRIM 712, RRIM 703 and PB 235.

NURSERY MANAGEMENT

Raise seedlings in nurseries for almost a year before transplanting to the field. This technique is more economical and convenient than direct planting.

Prepare germination beds. The length depends on the number of seeds to be sown. The width should be about one (1) meter for convenience in cultivation. Use fine river sand as germinating medium for minimum root damage when the seedlings are pulled out prior to transplanting. Aged sawdust or dried cogon can also be used.

About 2, 000 seeds can be sown per square meter of germination bed. Overcrowding of seeds can cause distortion of the roots which may cause difficulty during pricking. The seeds are closely laid on the surface with the top of the seeds on the level with the surface of the medium. They start to germinate in one week time. Continue watering until all viable seeds have germinated. Generally, survival rate from seeds to seedlings ranges from 80% to 90%.

During the months of August to October, rubber seedlings can be easily obtained from fresh, large, heavy and shiny seeds. For rootstocks, seeds of Tjir 1 are ideal because of the vigorous seedlings produced. Other clones are recommended for use except for PB-86 which produces albino seedlings.

Germination in seedbeds shall be done. It takes seven (7) days before transferring them to the polybag nursery, if green budding is going to be employed or in the ground seedlings nursery for brown budding. In which, after six (6) months, the seedlings are to be budded for 35 days and bagged afterwards. After a period of 4-6 months in the polybag nursery, the seedlings can be planted to the field.

Fertilize the seedlings with balanced fertilizer mixtures starting on the first month after planting of pre-germinated seedlings. Apply 10-15 grams per seedling or one teaspoon per application of NPK fertilizer mixtures, in two or three split dosages. Broadcast the fertilizer about 10cm away from the base of the plant.

PLANTATION ESTABLISHMENT / DEVELOPMENT

The maintenance program of the existing production area will basically involve the following major activities: fertilization, disease and pest control, ring weeding, cogon wiping and lining. Said maintenance program will give due consideration to: attainment of the highest possible yields, minimization of the loss/destruction of trees due to pests and/or diseases, and proper development of tree girth size.

For areas to be developed yet, the following practices shall be followed:

LAND PREPARATION

Plow and harrow the field which was previously planted with annual crops. If cultivation is needed, a tractor or an animal-drawn plow can be used. Plowing twice in cross direction during summer to expose and dry the rhizomes of weeds.
PLANTING DISTANCE

The avenue/hedge system is most suitable for hilly areas (10 m x 2 m). The rectangular or square method (4 m x 5 m) is recommended for flat or slightly undulating areas. For cash cropping and intercropping purpose, 2 m x 10 m or 2 m x 3 m x 21 m are recommended.

CONTOUR LINING/TERRACING

For hilly lands, the practice of contour lining/terracing is recommended. To minimize soil erosion, cutting of planting terraces is necessary. Cut the soil 20 centimeters in front of the line of the planting row back into the hillside to give a width of 40 to 150 centimeters with a backward inclination from the horizontal of 2.5 centimeters per 30 centimeters.

HOLING

A few weeks before transplanting, prepare the holes to condition the soil for quick growth of young shoots. The size of the hole depends on the nature of the soil and the planting materials to be used. In most cases, around 60 centimeters is being practice. Back filling is done at about 5 centimeters above the ground level.

PLANTING

Budded planting materials with at least two fully developed leaf whorls are recommended for field planting. In planting, remove carefully the bottom of the polybag using a sharp knife before placing the planting material in the hole. Make a vertical cut on the polybag starting from the bottom up to its upper surface. Fill the hole with loose soil until 3/4 full before pulling out totally the polybag. Tamper the soil around lightly with a wooden pole until about 2 inches of the ground surface is fully covered.

COVER CRIO ESTABLISHMENT

The three most common cover crops are Pueraria, Calopogonium and Centrosema. These are established either before or after field planting of rubber.

During the unproductive period, small growers can grow cashcrops. These can be planted between the rows of rubber to generate supplementary income such as cereals, legumes, vegetables and selected perennial crops.

REPLANTING

Replace vacant or dead hills with planting materials of similar age with that of the original stand for uniformity.

THINNING

This should be done during the third year to eliminate the less vigorous trees. This is the time when the branches and shoots start to close in.

FERTILIZATION

To produce high quality rubber, supply the crop with a balanced amount of essential nutrients, Nitrogen (N), Phosphorous (P205), Potassium (K20) and Magnesium (Mg). Nitrogen is commonly needed during seedling stage. This nutrient is essential for cell production for an increased growth and development of vegetative parts. Phosphorous is essential for cell division and development of growing tissues. Potassium (K) nutrients are needed especially by mature rubber trees. Bark regeneration is encouraged for a positive response to latex yield. For latex flow stability, Magnesium (Mg) nutrients are required.

For young rubber trees, (3 to 12 months after transplanting), the use of 65 grams of complete (14-14-14) fertilizer per tree is recommended. During the second year, 125 grams of 14-14-14 applied every six months is sufficient. From third year onward, higher rates can be applied yearly depending on the needs of the tree.

Fertilizer is applied on the soil layer within the 7.5 centimeters depth range. Distance from the base may range from 15 to 40 centimeters depending on the age and size of the tree.

Average fertilizer recommendation per tree are as follows: Nitrogen - 40 grams; Phosphorous 40 grams; and Potassium-30 to 135 grams.

PRUNNING

Start prunning the side branches that developed within the height of 2.75 meters above the point of scion stock union three weeks after planting until before tapping.
PESTS AND ITS CONTROL

Control of termites, root-feeding grubs and bark borers can be done through the use of recommended insecticides by pouring the diluted solution in the infested area. Sucking insects such as mealy bugs and aphids on the other hand, are controlled by spraying with soap emulsion especially if the infestation is heavy and spreading.

Rats and wild pigs destroying germinating seedlings and young plants can be controlled by baiting, trapping, hunting or by setting a barbed wire fence with wire netting about one meter high.

DISEASES AND ITS CONTROL

Diseases, particularly those caused by fungi, may infect rubber from seedling stage to maturity. Rubber diseases and their control are as follows:

1. Bird's Eye Spot (Helminthosporium hevea) Control: weekly spraying of Dithane M-45 (10% solution of 6 tbsp/4 gal knapsack sprayer) on fully expanded leaves.

2. Collectotrichum Leaf Disease and Anthracnose (Collectotrichum gloeosporoides) Control: spraying the expanding leaves with Vitigran Blue, Daconil, or Cupravit at the rate of O.2% or 2. a.i. per lt. of water (IO-Il Tbsp/4gal.) at least 4 rounds at weekly intervals.

3. Pink Disease (Corticium salmonicolor) Control: Bordeaux mixture (Lime, 0.36 kg; copper sulfate, 0.18 kg. or 0.4 lb., water, 15 lt. or 4 gal.) is sprayed on the infected parts but not advisable for trees in tapping.

4. White root Disease (Rigidoporus lignosos) Control: Regular inspection of tree. Those with foliar symptoms should be dried up and burned. Adjacent trees should be treated by carefully removing the earth from around the collar and the first 15 cm of the lateral roots. Cut and burn any infected wood. Application of Fomac 2 is also advised.

5. Stem Bleeding - There is no known control measure.

6. Black Stripe (Phytophthora palmivora) Control: Regular application of Aliette, provided the disease is detected early enough. For newly established diseases, a mixture of 10 gms per lt. of water at 20 ml per tree is applied every four days of tapping. For serious infection, a mixture of 20 gms per liter of water is used.

Apply fungicide by brushing with a 5-cm paint, brush to cover the entire infected area above the tapping cut and a strip just below the cut. Generally, a band 5-10 cm above and 2.5-5 cm below the cut is satisfactory.

7. Moldy Rot (Caratcystis fimbriata) Control: Moldy rot is spread by tapping knives or tappers' clothing. As a preventive measure, disinfect tapping knives after each tapping in the infected area by immersion in a fungicidal solution. The most effective chemical to control moldy rot is Benlate (Benomyl) at O.5% (5-6 tbsp. per 4 gal) applied four times at weekly intervals.

8. Brown Bast = Flow of latex in diseased bark finally stops due to coagulation of latex within the vessels. This cannot be controlled when coagulation has set in. Occurrence of brown bast can be prevented through proper tapping techniques and management.

TAPPING SYSTEMS AND BARK MANAGEMENT

In tapping, a thin shaving of bark is removed from the lower surface of the grove to open the latex vessels in the bark. The barks are blocked by plugs of coagulated latex The latex vessels are concentrated in the soft bark and the innermost layer of the hard bark, In tapping , therefore, the bark should be removed as close as possible to the cambium to serve the greatest number of latex-bearing vessels. However, the cambium should not be damaged so as not to hinder future tapping operations. The following tools are needed in tapping rubber trees: tapping knife, collection cup, vine cup holder and metal spout, a container for coagulant or anti-coagulant, and a basket for scraps.

Normal tapping system for rubber has an intensity of 100%. This is the s/2.d/2 tapping system. Intensive tapping has a tapping intensity of more than 100%. Since tapping intensity depends on the length of the tapping cut and the frequency of tapping, intensive tapping involves either an increase in the length of the tapping cut or tapping frequency or both. This system can be applied in old trees which are to be replanted within 10 years.

The system of double-half circumference cut to form a V-cut tapped once in two days is applicable on trees which are to be felled within two to three years. For areas to be replanted within a year, the multiple cut system or slaughter tapping method is recommended

The recommended standards for opening a rubber plantation for tapping are:

I. At least 7O% of the trees has reached the standard girth.

2. For hall circumference alternate tapping (s/2.d/2; half spiral, tapped every second day), trees should have attained a girth of at least 50 cm at 150 centimeters from the union. The girth is measured at the height of the lower end of the opening cut on the first panel.

A cut from "high left" to "low right" cuts a greater number of latex vessels per unit length of tapping cut than if the cut is made from "high right " to "low left ". For budded trees with thin bark, tapping is cut at an angle of 30 degrees to the horizontal. Normally, tapping is done over a period of two to three days. The oxidation of latex in the tree is governed by transpiration, hence tapping should be done early in the morning when transpiration is low to obtain high yield.

COLLECTING SYSTEM

Contamination of rubber latex must be avoided in order to maintain absolute cleanliness during tapping and collection of latex. Latex should be collected three hours after tapping the last tree in a block and placed in a clean plastic pail because the longer it stays in the cup, the higher the number of microorganisms that are introduced from the dirt and bark particles present in the tapping cut, spout. and collection cup. Containers made of plastic or non-corrosive metals should be used for this purpose. They should be cleaned and thoroughly washed after each use. If empty oil or kerosene cans are used, they should be painted with Epicote to prevent rusting. Containers used for latex collection should never be used for other purposes.

YIELD STIMULATION

Ethrel is the stimulant which is usually used in rubber due to its availability and satisfactory effect on rubber trees. Application can be done every two (2) months with a rest period of two (2) months coinciding with the wintering of trees. The stimulant is applied at a width of about 2.5 cm immediately below the tapping cut. This is usually done by slightly scrapping a strip of bark wider enough to be consumed in two months, e.g. 4 cm (I 1/2 inches) on alternate daily tapping.

The use of ethrel may necessitate reduction in tapping frequency, e.g. s/2, d/3, 67% half spiral every third day and s/2, d/4, 50% half spiral every fourth day. Application of complete fertilizer of high potash content is recommended at least once a year since ethrel stimulation results in excessive drainage of essential nutrients due to increased latex yield. Application rate must be based on yearly soil/leaf analyses.

Technology-advanced plantations advocate start of the ethrel application commencing from the eleventh year of tapping to avoid a faster decline in yields.

PRODUCTION PROCESS

Pre-Coagulation and Anti-Coagulants

Normal pre-coagulation occurs if collection and transportation are delayed. Abnormal pre-coagulation occurs during rainy days, wintering period and in newly opened young trees and high cut tapping. Normal pre-coagulation can be avoided or minimized by the addition of anti-coagu-lants such as ammonia and sodium sulfite
.
Pre-coagulation is manifested by lumps in latex cups. Clots in the latex, coagulation during transport and fermentation bubbles in the co-agulum.

Dilution, Standardization and Bulking

The separation of fine sand particles and dirt from field latex by straining alone is not practical due to the high viscosity of the latex. To facilitate separation of fine sand and dirt, the fluidity of latex must be increased. This is done by diluting it with water. Allowing the diluted latex to stand in property constructed tanks causes' sand and other fine particles to settle.

Since the quality of field latex varies considerably from field to field, the latex in a plantation must be brought daily to a certain standard by diluting the latex to reduce the dry rubber content (DRC). Generally, a 1: I ratio of water to field latex is used. The bulking tanks which are usually cylindrical with a conical bottom should have a drain tap below the level of the outlet to the coagulating tanks. Diluted latex settles in IO to 30 minutes. The latex flows from the opened outlet cock into a container if coagulation is done in pans or into a gutter which leads to the coagulating tanks. In plantations where there are no facilities for bulking and settling, it is essential to run diluted latex through a sieve to remove the line dirt particles and pre-coagulated lumps. Unless there is pre-coagulation, there is usually no need to sieve if bulking and settling are done properly.

COAGULATION

To bring the latex into a state suitable for coagulation, dilution is essential. Coagulation of the latex is carried out in aluminum coagulating tanks or wooden tanks lined with aluminum. Coagulating tanks are convenient for large plantations. The most commonly used tanks are 3 meters long, about 90 centimeters wide and 35 to 45 centimeters deep. it is important to provide slope on the bottom of the tank (l cm per 60 cm length) towards the drain to facilitate the flow of serum and wash water. Normally, the tanks are designed to contain 75-90 partitions. Both separate sheeting tanks which can produce separate 75 to 90 globe of coagulum and continuous tanks which can produce long continuous sheets are used.

For small plantations, rectangular aluminum pans having a capacity of 4.5 liters or halved kerosene cans may be used. Min-coagulating tanks capable of holding 36 liters of diluted latex to produce 8 sheets can also be used.

Although many substances can be used for coagulation of latex, only acetic and formic acids can be used as they are the only recognized standard coagulants. In practice, the acid required is computed and the solution is prepared by diluting it with water at the rate of 10 milliliter acid to one Liter.

While the acid is added, the latex should be stirred with aluminum or wooden paddles. Stirring should be done carefully to avoid internal bubbles and reduce internal surface foam to a minimum. A considerable amount of foam is produced with the mixing of diluted acid and latex. This should be removed with a. smooth wooden board or aluminum skinner to avoid the surface pitting of the sheet when the coagulum is rolled. The tanks or pans are then left as such without disturbing for complete coagulation.

When coagulation is complete, the tanks or pans should be flooded with water and left until machining starts. Since coagulum having all desirable qualities is very soft, it is easily deformed by careless handling. Excessive handling of the coagulum should be avoided as much as possible. In case of coagulation in tanks, a chute conveys the coagulum from the tanks to the sheeting battery. The coagulum can be floated directly from tanks. In other cases, it is to be lifted and placed in the chute, when pans are used for coagulation, the coagulum should be detached at the edges and carefully lifted from both sides of the pan.

MILLING

Hand or power-operated machines can be used for milling coagulum into sheets. One end of the coagulum is hand kneaded and passed through the first machine three or four times, the spaces between the rolls slightly decreasing each time. After this, the sheet is finally passed through the machine with grooved rolls whose nip is adjusted to give sheets of 2.5 mm thickness.

To handle large sheets, it is desirable to use a battery of rollers with set spacing. The sheets should successively pass from one machine to another. During machining, the water must be sprayed liberally over the sheets to remove the serum, excess acid and other soluble impurities. Sheeting machines are usually provided with water spray. In case this is not provided, the sheets are placed in a washing tank, and washed well in running water. The sheets are cut into a uniform length on a cutting table.

Source: DA, photo courtesy of www.panoramio.com