Irrigation systems are generally gravity-fed from streams that form from melting and precipitation upstream. The cool climate of Bhutan presents both a constraint and an opportunity. Most rice soils are loams or sandy loams. Zinc, however, may be a limiting nutrient in southern Bhutan. Insect pests are most serious in the humid low-altitude zone.
Weeds are a constraint to rice production throughout Bhutan.
In the high and mid altitudes, the most serious weed is Potamogeton distinctus. Weeds of rice in the low-altitude zone have not been surveyed systematically. Cropping patterns are constrained by temperature, rainfall, irrigation water availability, food preferences, and market opportunities. In areas where irrigation is available, farmers grow rice followed by wheat. In a few limited areas, two crops of rice are grown.