Irrigated lowland rice and rainfed lowland rice are characterized by a layer with low water permeability (‘plow pan’) in approx. 20 cm depth which is formed through intensive puddling of the soil. From an agronomic perspective, flooding of rice fields entails several advantages:
- less pressure from weeds and nematodes
- retaining water to buffer possible water shortages
- nutrient inputs through floodwater and sediments
- biological N2 fixation in aquatic systems
- easier tillage
- conservation of soil organic matter and fertility
- increased soil nutrient availability
- buffering of soil and canopy temperature
Basic facts about global rice production
- Rice is the most common staple food of the largest number of people on earth (3 billion people).
- Rice is grown on some 250 million farms. In Asia, it accounts for more than half of the agricultural harvested area in many countries and for 20-40% of total caloric intake.
- Worldwide, there are about 79 million ha of irrigated lowlands, 54 million ha rainfed lowlands, 11 million ha flood-prone areas (deep-water rice) and 14 million ha rainfed uplands (non-flooded rice).
- Growing rice takes a lot of water: 3,000-5,000 l per kg. Rice production consumes about 30% of all freshwater used worldwide. In Asia, flood-irrigated rice even consumes more than 45% of total freshwater used.
- By 2025, some 22 million ha of irrigated rice areas in Asia may face economic water scarcity (increasing costs for irrigation), an additional 17 million ha may confront physical water scarcity (supplies for irrigation simply dry up). Getting ‘more crop per drop’ (cf. Vince 2010) has thus become a major issue of rice production.