Rodents are reported in many countries as a major problem and birds are sometimes serious pests. Amount and distribution of rainfall and poor soil fertility are the most serious physical constraints. In Asia, the monsoonal rainfall ranges from 1500 to more than 3500 mm. Rainfall is usually erratic during the monsoon season. In Africa, annual rainfall ranges from 1200 to 2000 mm where upland rice is grown.
Rainfall is frequently erratic in semiarid areas of West Africa.
Mean annual rainfall in Latin America ranges from 1400 mm in central Brazil to 4800 mm in Costa Rica. Dry spells frequently occur during the growing season in most of these areas, mainly in north and central Brazil. In South and Southeast Asia, more than half of the upland rice is grown in infertile soils. In most upland soils, P rather than N is the most common limiting nutrient. Physiological disorders result from major and trace element imbalances.