ECOLOGICAL AND CULTURAL REQUIREMENTS OF GABI
Introduction
Gabi or taro is one of the most important root crops in the Philippines. Notwithstanding its widespread cultivation, this crop is commonly planted in areas not really suitable for its culture since traditional staples (i.e., rice and corn) and vegetables are given priority to occupy good production areas. Although gabi has the ability to grow in marginal and submarginal areas, it normally grows well and produces high yield when cultivated in more suitable areas favored with the right soil and rainfall needed by the crop.
Apart from the ecological needs of gabi, good growth and yield is better insured when appropriate cultural management is given to the crop, hence this digest has been prepared to give one an insight to the basic requirements in its culture.
Ecological Requirements
Soil
Gabi can be grown in a wide range of soil types either as upland (dryland) or lowland (wetland) crop. The term upland refers to gabi production under a non-flooded condition and does not necessarily mean growing in high elevations. Under upland culture best results are obtained on deep, well-drained loam soil. Under lowland cultivation, which is usually in low-lying areas with abundant supply of fresh cool water for irrigation, best results are obtained if the soil is alluvial. In either culture, soil pH ranging from 5.6-6.5 is reported to be best. Although gabi can be grown in water-logged areas, it does not usually grow well in these places because the temperature build-up of the water during hot days causes the plant to respire more.
Rainfall
Gabi is best adapted to a warm and moist environment. Evenly distributed rainfall is ideal especially for upland gabi. In areas with distinct dry and wet periods, planting upland gabi should be timed in such a way that the first four to five months of growth should receive a good amount of rain. For lowland gabi, as long as there is a continuous supply of fresh and cool water, rainfall pattern is not critical.
Temperature
A daily average temperature of 27-29C is ideal for gabi. Below 27C, yield is reduced. Likewise, above 29C the plants are stunted and yield is greatly depressed.
Cultural Requirements
Land Preparation
The method of land preparation generally depends on the culture used, whether upland or lowland. Upland fields for gabi production is prepared in the same manner as that for other crops like corn. The field is plowed and harrowed thoroughly to kill the weeds and pulverize the soil. When labor is scarce, one plowing followed by harrowing is enough as long as existing weeds are properly controlled. After the soil is thoroughly prepared, furrows are set. If flat planting is preferred, setts (planting materials) are planted without making furrows.
For lowland culture, the field is prepared in a manner similar to that of lowland rice. Existing weeds are first removed by cutting mechanically or by hand, then the field is plowed and harrowed both to puddle the soil and to flatten the area to ensure even distribution of irrigation water. When the field is thoroughly prepared, lines are drawn using a lining board or an ordinary string as planting guide.
Planting Materials
Planting materials are called setts. A sett is prepared from a plant or daughter plant, i.e., either sucker or rhizome. It consists of the upper 1-2 cm of the corm or cormel plus the lower 20-25 cm of the petioles. Best results are obtained with a sett size of 100-120 g. Smaller-sized setts can be used but maturity is delayed. Planting materials should be uniform in size but if different sizes of setts are used, plant together those that are more or less of the same size.
Cormels can also be used as planting materials but these are easily attacked by disease-causing organisms.
Planting Distance
The recommended planting distance is 75 cm between rows and 50 cm between plants in the row. Closer planting at 50 cm x 50 cm may be done but the size of individual corms gets smaller as planting distance becomes closer. Both of the above mentioned planting distances are applicable for upland and lowland culture.
Planting Method
Under upland culture, gabi can be planted in furrows or in flat beds (without any furrow) with the help of a bolo or a stick. If flat culture is preferred and irrigation is not possible, setts should be planted deeper (8-10 cm) during dry months and shallower (4-5 cm) during wet months. Mulch to conserve moisture and control weeds can be spread around the gabi plants. If labor is not a problem, planting can be made in holes about 15 cm wide and 20 cm deep. A sett is placed in one hole and is partially covered with soil. As the gabi grows the holes are naturally and slowly filled with soil.
In the lowland, planting is done in flat fields and setts are just inserted about 4-5 cm deep by hand into the puddled soil.
Fertilizer Application
It is important to determine first the nutrient status of the soil before planting gabi. If the soil is rich in organic matter, inorganic fertilizer may not be added. If the soil is rather poor, apply 30-30-30 kg/ha N, P2O5, K2O or more if necessary. Apply 1/2 of the total fertilizer requirements upon planting and the other half 2 months after planting. The same should be done for lowland culture but the field should first be drained of water before fertilizer application. Side dressing brings better fertilizer effect in contrast to broadcasting followed under upland culture. Under lowland culture, broadcasting is practical because there is sufficient moisture to dissolve the fertilizer at once.
Weeding and Cultivation
Gabi is especially sensitive to weed competition. In both lowland and upland cultures, the fields should be rid of weeds particularly during the first 8-10 weeks after planting. However, weed competition after this period should not be tolerated especially if plant canopy has not yet closed.
For upland culture, weeds can be controlled mechanically by hand weeding or by means of plowing the inter-row spaces during off barring and hilling up operations. Chemical weed control is good as long as the plants are thoroughly protected.
For lowland culture, it is enough that weeds are properly controlled. This can be done by regulating the water depth in the paddy.
One good way of controlling weeds in upland gabi is by planting intercrops. Legumes, especially mungo, is a good intercrop because of its short growing period and early maturation before the gabi canopy closes.
Pest Control
Insect pests like aphids, army worms, hornworms and grasshoppers attacking gabi plants can be controlled by spraying appropriate insecticides. For gabi disease like leaf blight, the application of fungicides is an effective control practice. For plants that show symptoms of virus infection, removing and burning the plants are good control measures.
Harvesting
Time of harvest depends upon the variety used although normally upland gabi matures earlier than lowland gabi. The best indication of maturity in gabi is the size of the corm. A physiologically mature gabi plant has leaves turning yellowish and petioles becoming short but this should not be mistaken for drought effect.
Source:
Root Crop Digest
Vol. 2 No. 3 1987
PRIS ISSN 0016-4325
ECOLOGICAL AND CULTURAL REQUIREMENTS OF YAM
Introduction
Ubi (Dioscorea alata) and tugui (Dioscorea esculenta), are the two most important yam varieties commonly cultivated in the Philippines. They are cultivated in small patches of land, oftentimes less than a hectare, particularly in some regions of the Philippines like the Ilocos, Southern Tagalog, Bicol, Central Visayas and Northern Mindanao. Yam tubers, which are often very expensive, are used mainly for food either as substitute for staples like rice and corn or as ingredient in some vegetable preparations and in various food delicacies.
Successful cultivation of yams requires some knowledge on the growing conditions and cultural requirements of the crop. Due to the inadequacy of information on yams in the Philippines largely because these crops have been neglected in the country for so long, this publication attempts to supply the needed information particularly on its ecological and cultural requirements.
Ecological Requirements
Vine Support
Yams are climbers hence their vines need stakes for better display of leaves. Plants that are not provided with stakes yield less than those with stakes.
Soil
Yams are upland crops and they should be planted in a well-drained field. Optimum yields are obtained from sandy loam and silt loam soil although acceptable yields are also obtained from clay loam soils, particularly those high in organic matter. Stony and highly compacted soil should not be planted to yams.
Elevation
Cultivation of yam is done usually at low and medium elevation. In general, yields of yam are reduced above 900 meters, although it is reported to be grown at elevations up to 2,700 meters.
Water
Although yams are relatively drought-resistant, they require ample moisture throughout their growing period, particularly from 14 to 20 weeks after planting when tuber bulking occurs rapidly. Irrigation should be provided in areas where the dry season is longer than 3 or 4 months and falls within the growing period of the plants.
Temperature
Yams require temperatures ranging from 25C to 30C.
Day Length
Yams respond to length of daylight periods. Short daylights tend to favor tuber formation while long daylights favor vine growth.
Cultural Requirements
Land Preparation
For a field that has been cultivated previously, two plowings and two harrowings are usually enough for yams. However, plowing should be made deep since yams need a deep loose soil.
The flat bed and the ridged bed types appear to be preferable to the other types of seedbed. When the latter is used, the ridges should be constructed one meter or 60 cm apart. In the case of sloping or rolling fields, construction of ridges should follow the contour to minimize soil erosion.
Preparation of Setts
In yams, setts are whole tubers or tuber pieces used for planting. For ubi, whole tubers and tuber pieces are used while only whole tubers are used for tugui. Setts weigh from 60 g to 250 g in the case of ubi and 100 g to 150 g in the case of tugui. As a rule, the bigger the sett used, the higher is the expected yield although the increase in yield for every unit increase in sett weight decreases.
Setts should be taken from healthy tubers of healthy plants. In ubi, tubers of appropriate sett size are not sliced while larger tubers are sliced into the desired sett size so that each sett has sufficient skin surface area. Thus in ubi, four types of setts are obtained and are named according to their positions on the tuber viz: head setts, middle setts and tail setts for the tuber pieces and whole setts for the whole tubers.
Cut sides of the setts are treated with ash or with fungicide and air dried. After air drying, setts are either pre-sprouted or planted directly.
Pre-sprouting of Setts
Because the emergence period of most freshly prepared setts in the field lasts from three to twelve weeks, it is desirable to pre-sprout the setts before they are planted. This procedure assures the emergence of setts in the field and minimizes expenses on weeding before sett emergence.
A shallow ditch is dug in a clear shaded area under trees, under bananas, or under a shed constructed for the purpose. Setts are placed side by side in the ditch. In cases where no ditch is dug, the setts are placed side by side on the ground instead.
Setts are grouped according to type. For setts cut from large tubers, the orientation is either skin up or crown sideways. Setts are covered with a thin layer of soil and are watered at least once a week until all have produced sprouts.
With sett pre-sprouting, it may be desired to stagger planting and land preparation since setts do not sprout at the same time. In general, whole setts and head setts sprout ahead of other sett types. Planting pre-sprouted setts can, however, also be done at one time.
1. Preparation of pre-sprouted setts for staggered planting.
To prevent sprouts from becoming too long, setts that have already sprouted are removed from the pre-sprouting seedbed and placed on a platform in a shady place. The process is repeated every week until the desired number of sprouted setts is obtained. The sprouted setts on the platform are not watered. Setts are planted before sprouts become very long.
The same procedure is performed for setts intended for the second and succeeding plantings.
2. Preparation of pre-sprouted setts for single planting.
The procedure followed in single planting is essentially the same as that used in preparing setts for staggered planting. The former is done only after most, if not all, setts have produced sprouts. By this time some sprouts which shall have grown quite long should be trimmed before the setts are planted.
Planting
The usual planting time for ubi is March to May and occasionally until June, depending upon the time the tuber dormancy is broken, as indicated by the sprouting of tubers under storage and upon start of rain in a particular area.
In staggered planting, the field is divided into four up to six sections - a section for a batch of setts ready for planting. The size of each section and the time each section is prepared is guided by the rate of sprouting of setts.
Mulching
In order to reduce soil temperature, conserve soil moisture and suppress weed growth, it is preferable to mulch the field planted to yams. Dry coconut fronds, corn stalks, rice straw and other similar materials may be used as mulch. If rice straw or similar material that rot readily is used, the mulch is made thick (about 10 cm) so that it will not rot completely within four or five months.
Weeding
The number of times an ubi field needs to be weeded depends upon the use of pre-sprouted setts, the application of mulch and the rate of weed growth. If non-pre-sprouted setts are used and the field is not mulched, three to five weeding operations are needed before the yam canopy covers the space between rows to partially suppress weed growth. If pre-sprouted setts are used and the field is mulched, at most only two weedings performed about two months apart are needed.
Handtools and animal-drawn implements are used to weed the field. While plants are still short and unstaked or if the stake structure allows their use, animal-drawn implements are used in an unmulched field. This requires that vines that cross the path of the animal be first removed and placed along the rows. However, if the plants have been staked and the stake setup does not allow use of animal-drawn implements or if the field is mulched, only handtools are used.
Replanting
Some amount of sett mortality can be expected, particularly in ubi when non-presprouted setts are used for planting. Thus replanting is done, usually about two months after planting.
Hills with no sprouts are checked to see if there are rotten setts which should be removed and replaced with new ones. Unsprouted setts that did not rot should not be replaced because they still can produce sprouts later.
Hilling Up
In the case of unmulched ridge seedbed, rain and handweeding operations often level down ridges. Thus, it is necessary to hill up at least once about two or three months after planting.
When the plants are still short and unstaked, animal-drawn implements may be used in hilling up. In this case, the vines that cross the path of the animal are first lifted and placed along the rows. When stakes are already set up and their presence do not allow the use of animal-drawn implements, handtools, usually shovels, are used.
Staking
Plants are staked before vines start crawling on the ground. The recommended stake length is one to two meters and a stake to every plant. Bamboo poles, wood, cassava stalks, talahib stalks or any similar material that can support the yam vines for at least seven months can be used as stakes. If cassava stalk is used, it is set up in an inverted position (top portion buried) so that it will not produce new shoots. There are various methods of staking, three of the more popular ones are as follows:
Training the Vines
The ubi vine twines to the right while that of tugui twines to the left. When vines start crawling on the ground, they are trained to climb their respective stakes. They are trained again when long branches start crossing the rows or when weeding and hilling-up operations using animal-drawn implements are about to be done.
Fertilizer Application
A hectare of ubi is able to remove about 128 kg nitrogen, 17 kg phosphorous and 162 kg potassium from the soil. This represents more or less its fertilizer requirements. In the case of tugui, no information is available regarding the amount of nutrients it can remove from the soil. However, like other yams, its fertilizer requirements is probably similar to that of ubi.
The level of soil fertility in the field and the amount of fertilizer that need to be added are first determined by submitting the soil samples to the Bureau of Soils for analysis. The assistance of the local Farm Management Technician should be sought regarding this.
Covering Exposed Tubers
As tubers elongate rapidly towards the end of the growing period of the plants, some tubers tend to heave, thereby causing them to be exposed to the sun. Heavy rains also expose the tubers. Exposed tubers should be covered with soil to prevent them from greening.
Harvesting
Ubi is ready for harvest when its foliage is already yellowing or drying up. In tugui, only the basal leaves turn yellow; the rest remaining green, even when new sprouts have already emerged from the base of the plant. The yellowing or drying up period of the foliage usually starts in late November and lasts until February the following year. In general, ubi matures ahead of tugui by about one month. Tubers, especially those intended for setts, are harvested at the later part of the period. Tubers intended for consumption or for the market are sometimes harvested earlier, even before foliage yellowing sets in.
A bolo or a similar handtool is used to dig around the tuber to loosen it from the soil. Then the tuber is lifted and clinging soil particles are removed. The vine is cut at the base.
For sandy soil, sturdy stick sharpened at one end is sometimes used to dig out the tuber. For clay soil and for varieties with deeply buried tubers, an ubi harvester devised at PRCRTC may be used. The harvester is used like a shovel. Whatever tool is used to harvest the tubers, it is important that care should be exercised so as not to injure them while digging.
After tubers are cleaned, they are collected and placed in rattan baskets or bamboo or wooden crates lined with soft materials such as banana leaves, paper or grass straw. Healthy and diseased tubers are placed in separate containers. The tubers are arranged in the container in two to four layers, depending upon tuber size, and a soft material that can serve as cushion is placed between layers and in the spaces between tubers in a layer. The container is then covered with paper or banana leaves and a string net is woven over the mouth of the container if the tubers are to be transported immediately to the market. No cover is provided for the container if the tubers are to be transported to a nearby storage place.
The tubers should be transported with minimum of jolting using a cart or a sled.
Source:
Root Crop Digest
PRIS Vol. 2 No. 4
1987 ISSN 0116-4325