In the wet zone, ricelands are situated mainly on terraced slopes and narrow inland valleys of the highly dissected middle peneplain. Production constraints Sustainability problems have begun to surface in recent years, especially in the highly productive areas of the dry zone. Increasing costs, reducing profits, flat or declining yields, and micronutrient deficiencies are observed. Drought in rainfed areas and water shortages in irrigated areas are more frequent than before in the dry zone. As a result, the area grown to short-duration varieties has increased considerably.
Seasonal flooding is a regular occurrence in the coastal plains of the wet zone.
In the wet zone where ricelands are situated in the valley bottoms, low solar radiation is the major limiting factor for high yields. The geographical location of the dry zone ensures favorable air and soil temperatures as well as adequate solar radiation for rice cultivation throughout the year. Although salinity and alkalinity are reported, only minor soil chemical problems are encountered on soils of the dry zone. In poorly drained ultisols of the wet zone, P and K deficiencies, and Fe toxicity are common. Peaty and acid sulfate soils are found in the coastal plain.