CROP

- Harvest
- Rice farming systems

Harvest

Depending on the weather and the cycle of the varieties, it is possible to obtain from one to four harvests per year.

In tropical climates, rice is generally harvested twice a year. Sometimes, there are three harvests as in Vietnam and the Mekong Delta. Up to four harvests have taken place in China. The main harvest normally occurs between December and February.

In temperate and cold tropical climates (in high altitude areas), there is only one harvest per year - from September to October in the Northern Hemisphere and from March to April in the Southern Hemisphere.

Many factors must be combined to ensure a good harvest :
- Adequate temperatures (the zero-physiologic is 12°C for Japonica and 13°C for Indica);
- Enough water;
- Careful work.

The necessity of warm temperatures is not the major obstacle. Higher temperatures are only indispensable during the maturation period (at least 20°C for 25 to 40 days). Rice can bear seasonal variations of temperatures in Mediterranean regions, where winters can be cold, since water supply is regular and abundant during the growing period. In high altitude areas, adapted varieties can tolerate low temperatures (12°C in average) at night.

Productivity

- World average productivity: approximately 3,9 tons per hectare;
- National maximum productivity: nearly 9,5 tons per hectare in intensive irrigated systems (Australia);
- National minimum productivity: approximately 0,75 tons per hectare in traditional upland rice systems (Congo Republic).

In most regions where the upland system predominates (Africa and mountain areas in the Southeast Asia which are characterized by burned areas and long 8-to-15 year rotations) the yields are low, with the exception of Brazil (intensive mechanized systems). Land easily deteriorates if handling practices (rotations and no tilage) are not quickly adopted. On the other hand, even without intense mechanization, irrigation allows very high productivity as in Australia (9,5 ton per ha) and Egypt (8,7 ton per ha).

Rice farming systems

The rainfed lowland rice

- It grows over a compacted soil (mainly in Africa and Madagascar), in bunded fields able to retain between 0-25 centimeters (low level) and 25-50 cm (medium level) of water. Rainwater or a local reception tank, passing from one paddy to another by gravity, feeds this non-irrigated rice. The rainfed lowland rice is also cultivated in deep water (50-100 cm), therefore excluding semidwarf varieties. The risk of temporary drought and unexpected floods is the major concern in this production system.
- Fertilizer utilization is rare. Introducing this type of cultivation, often associated with direct seeding and transplanting, is difficult and yields are low.
- This type of rice system represents 25 percent of the total rice area and 17 percent of world production, ranking second after irrigated rice.
- This rice farming system is located in rural regions where populational density is high, often in the poorest rural and urban populations.

Upland or dryland rice (in mountains or plateaus)

- Land is prepared for planting and rice is dry-seeded. Lack of humidity and normally poor soil affect crops and yields are often very low;
- This ecosystem is found in Brazil (Center-West), Madagascar, India and southeast Asia. In Asia it is observed mainly near the river banks when the water goes down at the end of the rainy season. In some African and Latin-American countries it represents more than 50 percent of the total rice area;
- Upland rice represents approximately 13 percent of rice planted area in the world and 4 percent of global rice production.

Irrigated rice

- Land is prepared while wet. Water is held in little reservoirs. Transplanted rice is most common in Asia. Elsewhere, direct seeding is used more and more due to increased labor costs.
- In the transplanting system, seeds are pregerminated and grown in wet seed-beds for a period extending from 9-14 days in Madagascar to 40-50 days after sowing in Asia. The seedlings are then transplanted.
- In direct seeding, seeds are frequently pregerminated. They may be broadcasted by hand (in Asia), machine-drilled in puddled soil or drill-seeded into dry soil, or even spread over the water by airplane (as in the United States and Australia).
- Fertilization helps increase productivity, especially with semidwarf varieties or high-yielding varieties from the Green Revolution. Mineral, organic and ecological fertilizers are applied.
- Rice productivity may obtain 5 tons per ha during the rainy season and more than 10 tons per ha in the dry season, when adapting advanced technologies.
- Irrigated rice accounts for 55 percent of the world rice area and about 75 percent of world production.

Deepwater or flood-prone rice

- Water is 1 to 5 meters deep and is supplied by rivers, lakes or tides in river mouth deltas. Water depth may exceed 5 meters in some parts of Bangladesh, as well as in the Mekong, Chao Phraya and Niger deltas.
- Seeds are broadcasted in ploughed fields, normally unbunded, in regions where the water level rises quickly after the beginning of the monsoon.
- Traditional long tiller and few sprout varieties are cultivated. The plant elongates and floats as the floodwater advances, thus its name - "floating rice".
- Deepwater rice is found in south and southeast Asia (Bangladesh, Thailand, Cambodia, Sumatra), West Africa and South America.
- Productivity is low, mainly due to climate risks (droughts and floods) and the low production potential of cultivars grown with few inputs. Nevertheless, this ecosystem meets the needs of more than 100 million people, most of them living on small family farms.
- The construction of dams and other hydraulic projects has led to the transformation of some parts of Bangladesh, India, Thailand and Vietnam into irrigated rice areas.