The word that fits in the blank is "tariff".
A tariff is a tax that a government imposes on imported goods. By imposing a tariff on imported coffee, the Ugandan government makes it more expensive for local customers to buy coffee from other countries. This gives local coffee growers like Dabasso an advantage because they can charge a lower price for their coffee and still compete with imported coffee. Therefore, Dabasso counts on the fact that the Ugandan government has placed a tariff on imported coffee because it makes it easier for him to compete.