Key Words and Phrases: - eCommons@Cornell - Cornell University

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In large plantations in Barbados and Jamaica, yam production is largely mechanized (Jeffers,
1990). Af~er harrowing, subsoiling and furrowing, ridges are made about 1.70 m apart and yam sets
are spaced 0. 75 to 1.50 m on top of the ridge. Yams are also sometimes planted in trenches or pits
(30 x 30 x 30 em) filled with good soil. This practice is common in many South Pacific island
countries (Coursey, 1971).
E. Taro and Tannia:
For lowland taro the soil is thoroughly puddled after soaking for several days. Cormels are then
planted in the drained soil, either on the flat or on small ridges (10 em high). Shallow flooding after
establishment will enhance growth and hasten maturity (Ghosh eta/., 1988). For upland taro and
tannia, the field is generally plowed to incorporate compost or manure, followed by harrowing and
sometimes ridging or mounding.
Research on Tillage Practices
Tillage practices for root crops have not been thoroughly investigated and most research has
been of an empirical nature to determine the best tillage practices for a particular soil. Still, Vine
(1980) reported that cassava responded more to particular soil conditions rather than to a particular
tillage practice. Little research has been conducted to define the optimum soil characteristics, such as
bulk density, soil penetrability, infiltration rate, etc., for the various root crops.
Moreover, these
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physical soil characteristics, which are affected by tillage practices, are seldom determined. Thus,
most researchers conclude that root crops need a light or loose soil, but that the best method of land
preparation 'depends on the soil type, topography, vegetation, climate and the degree of
mechanization or other agronomic practices used (Seixas, 1976). In light soils (Lal, 1985) or in newly
cut and burned forested areas, very little cultivation is usually required, while in heavy or compacted
soils, root crops respond favorably to plowing and harrowing, and under certain conditions to
subsoiling or· ridging.
I. Effect of tillage on soil characteristics:
The main objective of tillage is usually to loosen the soil and incorporate weeds, crop residues,