With average estimates of 53 t/ha, tomato yields in Vietnam
were high when compared with those of Thailand (20 t/ha) and
Tamil Nadu, India (25 t/ha). Yield not only varied across countries,
but also within the countries, as indicated by high standard deviations.
For Thailand, the coefficient of variation (CV) was nearly
100%. This finding confirms those of Huat et al. (2013) who studied
tomato yields under tropical conditions on the island of Mayotte
(Indian Ocean). The greater yields in Vietnam could in part be
explained by the widespread use of grafted seedlings against soil borne
diseases (31% of the farmers had adopted it), the use of
plastic mulches to control weeds and to maintain soil moisture, and
careful management including pruning, irrigation and fertilizer
application. The length of the growing period for tomato also was
longer in Vietnam than in Tamil Nadu and in Thailand, where
production was less intensive. Most farmers in Thailand tended to
plant tomatoes on the same plot of land without alternating it with
a crop from outside the Solanaceae family. The use of plastic
mulches or drip irrigation systems was less common in Tamil Nadu.
Moreover, it was also common for farmers in Tamil Nadu to prefer
growing low yielding open pollinated varieties rather than hybrids,
as the open pollinated varieties had better market appeal in terms
of taste, acidity and appearance; this contributed to crop yields in
Tamil Nadu being less than half than achieved in Vietnam.