2.3. Paddy fields in the dry region

Paddy fields are found even in dry region, where rainfall effective to rice growth is not expected. They fundamentally cannot be cultivated without irrigation, where consequently rice is grown in fields with surrounding ridges to keep water. They are generally to maintain 5–10 cm of water, and usually puddled and rice are transplanted. The paddy fields reclaimed in the arid zones are recognized as the typical artificially created wetland.

Paddy fields in the dry region are irrigated and require much water to maintain flooding, since ponding water evaporates much into the atmosphere and seeps much into the soil profile that is generally much sandier compared with the paddy field in the wet regions. Basically in the dry region or dry condition, water availability is limited, and consequently the development of paddy production or paddy fields that requires much water is not preferred. Even with this constraint, actually there are many paddy fields in those conditions. There must be some reasons for the expansion of them with definite advantages.

First, the people in the dry region like the taste of rice. Second, rice contains much nutrients compared with wheat and maize as main cereal crop. Calorie per grain weight of rice is larger than wheat and maize. Protein of rice is less than them, while its quality of rice is better than others for human health. Maize contains much lipid, while its contents of rice and wheat are almost the same.

In addition to the advantage of rice in terms of the nutrients of the grain, land productivities of these crops are quite different. The weight of grains harvested per area of rice is almost 1.5 times of wheat. Furthermore, rice can be cultivated every year continuously in the same field, and the land used as paddy field can produce stable harvest.

Rice has another advantage of grain including its easiness for cooking and longer preservation. Although paddy cultivation, however, needs much labor in terms of time and efforts to maintain the field and its surrounding ridges and to perform water management, its advantages promote expansion of paddy fields even in dry region or condition.

These challenges have created the artificial wetlands in dry region.
