Cultivation

Cultivation

    Soil
    Dioscorea can be grown in several types of soils. Light or sandy soils require heavy irrigation and fertilization whereas heavy clay soils restrict tuber growth and harvest and often create water-logging. The bet yields are obtained in medium loam and in deep soils which are rich in organic matter. In red, soils, the best growth has been observed for both D.floribunda and D.composita. It tolerates wide variation in soil pH, but highly acidic and highly alkaline soils should be avoided.

    Climate
    The different species of Dioscorea are found growing in different climates, but while D.floribunda and D.composita are more suited to the tropics, D.deltoidea is reported to be a suitable species for temperate locations. It grows well in the temperate regions of Kashmir and Himachal Pradesh.

    Land preparation
    The field should be ploughed and harrowed several times, leveled properly and drainage channels should be made. Since yams have a high requirement of organic matter of good tuber formation, a recommended quantity (20-25 t/ha) of FYM is incorporated at the time of land preparation. A spacing of 45 x 30 cm for a 1-year-old crop and 60 x 45 cm for a 2-year-old crop in D. floribunda is found to be optimum under irrigated conditions. For planting, deep furrows are made at 60 cm distance and sprouted tubers are planted in furrows at 5 cm depth. After sprouting is completed, earthing up is done, utilizing the soil from the ridges. D. composita and D.deltoidea are reported to give higher yields at spacing of 60 x 30 cm and 30 x 70 cm, respectively.

    Propagation
    The yams can be propagated either by seeds, rhizome pieces or stem-cuttings. In India, commercial plantations are raised from tuber-cuttings. Seed progeny is variable and takes a longer time to start yielding tubers, compared to plants raised from tubers. The choice of propagating material will depend on the cost of planting and the prevailing climatic conditions of the region.
    a)Propagation from tuber pieces
    This crop grows best from tuber pieces. Tubers or rhizomes are divided into approximately 50-60 g pieces for planting. The growth of plants is slow and the yield lower if smaller pieces are used for planting. There are 3 types of pieces (1) Crowns (stem end), (2) Medians (middle portion) and (3) Tips (distal ends). Crowns produce new shoots within 30 days of planting, while the others take nearly 100 days to sprout. Besides, the crown portion contains less diosgenin compared to the median and the tips, hence the later can be used for the extraction of alkaloids and the former can be used for propagation. But, if there is a shortage of planting material, the median and tips can also be used for planting.
    In order to avoid the rotting of tubers (before sprouting), only healthy tubers should be selected. The healthy tubers must then be dipped in benlate fungicide (0.3%) for 5 minutes followed by dusting the cut ends with 0.3% benlate powder before planting or storage.
    Before planting the tubers directly in the main field, they should be stored in a moist, well-areated rooting medium until shoot growth commences. The benlate-treated tuber pieces should be kept in raised beds in the shade, covered with sand and watered daily. After 30 days the sand may be removed and the sprouted crowns taken out and planted in the field. The median and tip portions are again covered with sand and watered regularly. Subsequently, after 60-75 days when they have completely sprouted, they can also be planted in the field.

    Season of planting
    The tuber pieces can be planted either in February-March or June-July. In Karnataka, February-March planting is better. For medians and tips, it is better to plant from the middle of January because they take more time to sprout compared to the crowns. The new sprouts will grow vigorously during the rainy season which commences from June.
    b)Propagation by seeds
    Propagation through seeds is much more successful in D. floribunda and D. composita, as compared to the other temperate species. The seed has a wide membranous wing that can be removed without affecting germination. The seeds can be sown either in raised beds in the shade (with a mixture of loamy soils and FYM) or in polythene bags (filled with sand, soil and FYM; 2:1:1). The planting depth should not be more than 1.25 cm and frequent watering of the beds is essential. The seeds germinate within three weeks and are ready for transplanting in 3-4 months. The seedlings should be supported immediately.
    The best season for transplanting the seedlings to the field is just before the start of rains, i.e., in June in South India, but in North India, this can be done at any time except during the winter.

    Seed production
    Since dioscorea is a dioecious plant, female and male plants should be grown close to obtain the seeds. Under South Indian conditions. Excellent seed set is noticed. Flowering starts from August and the seeds mature from December to February. The pods turn brown and dehisce along with the upper margin. The harvested seeds should be stored in airtight plastic bags where they will remain viable for 3-5 years.
    c)Propagation by stem-cuttings
    D. floribunda can be propagated by stem cuttings with 80% success. The vines should be raised from 50-100 g tuber pieces in the green house. One or two month-old vines are taken and cut into single node cuttings, each with one leaf. They are planted in sand-beds keeping the leaf blade above the sand. Before planting, the cuttings should be treated with 100 ppm 2,4-D and 0.1% benlate for 4 hours. The beds should be watered regularly, after rooting the cuttings are transplanted to polythene bags and produce about ten leaves in a period of two months.
    Propagation of D. floribunda can also be done by air-and ground-layering. Application of NAA at 100 ppm was found to be most effective for getting 80-90% rooting.

    Provision of support
    The vines need support for their optimum growth, as this exposes the maximum number of leaves to sunlight. The system tried successfully at Bangalore consists of 2 m-high, stone pillars spaced 9 m apart in the field. Galvanized wires (Nos.6 and 8) are used on the boundaries and the interconnecting wires can be of 12 gauge thickness. The vines are supported on coir ropes tied to the wires and pegged to the ground by wooden stakes.

    Manures and fertilizer
    A well decomposed FYM of 20-25t/ha is applied while preparing the land. Yams respond very well to fertilizer application. A fertilizer dose of 300 kg N, 150 kg P2O5 and 150 kg K2O/ha, has been found to be optimum for a one-year-old crop of D. floribunda. The entire quantity of P should be applied as a basal does, while N and K are given in four equal split doses at bimonthly intervals commencing from 2 months after sprouting. For D. deltoidea, for a 4-year-old crop, the recommended fertilizers under Kashmir conditions are 40 kg N, 80 kg P2O5 and 60 kg K2O in split doses at an interval of one month from the time of planting in the first year and the same quantity in the second year. In the third year, only N at 30 kg/ha has to be applied in two split doses. For increasing the tuber yield and diosgenin content, the application of S, Ca and Mg has also been recommended.

    Irrigation
    The crop needs irrigation frequently during summer months. An interval of 4 to 5 days in summer and 7 to 10 days in winter is desirable for the proper growth and development of this crop and for economic yields.

    Interculture
    In the initial stages, yam plantations require more frequent hand-weeding than in the later stages. Chemical herbicides have also been tried, but are not recommended commercially. Studies have revealed that it is feasible to intercrop medicinal yam with short duration crops like cowpea, cluster beans and kidney beans, where irrigation is available. This practice not only minimizes the growth of weeds but also gives additional returns. Apart from this, intercropping also helps in reducing the requirement of nitrogen as these crops are leguminous.


Last modified: Friday, 22 June 2012, 5:34 AM