3.1. Water management in paddy plot

Rice cultivation has some superiority on food production mentioned above. On the other hand, paddy fields, where rice is grown, need much water due to its flooding. The main reasons why paddy fields are flooded is that most rice varieties realize better growth and produce higher yields in flooded farmland than in dry field.

In most cases, the water layer of some centimeters in a field is established usually after transplanting of rice seedlings and maintained until few weeks before harvesting. The typical water management of paddy field with standard depth of flooding for each growing stage is shown by FAO [10], and it is summarized in Table 1 with supplemental explanation of GriSP [1].

Actual water management practices on water application and flood depth control are affected by field conditions including:

1. cultivar of rice,

produced in the area, of which water condition is fully or partly controlled by humans like

In the third category "flood-prone field," deep-water rice and floating rice are grown in the uncontrolled flood environments, suffering periodically from excess water and deep flooding, sometime with deeper flood of 100 cm for some certain part of the growing season. This covers

The last, forth category "upland," is a field where rice is grown under dryer conditions, without ponded water, and then it is not surrounded by ridges to keep water and not equipped with irrigation system. The area of "flood-prone" and "upland" is about 11 and 15

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

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

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

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,

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 advan-

in the arid zones are recognized as the typical artificially created wetland.

reasons for the expansion of them with definite advantages.

and the land used as paddy field can produce stable harvest.

tages promote expansion of paddy fields even in dry region or condition.

These challenges have created the artificial wetlands in dry region.

farmers.

about 15 million ha.

146 Irrigation in Agroecosystems

almost the same.

million ha, respectively [1].

2.3. Paddy fields in the dry region


In the improved paddy field with stable water supply and enough drainage capacity, independent water management practices of farmers are implemented, where the farmers can apply and drain water whenever they want and they introduce advanced techniques and materials.


Table 1. Typical water management of paddy field with standard depth of flooding.

Under these conditions, the field water condition including flooding period and depth is controlled considerably. For some periods, they drain water intentionally resulting in no submergence for some periods, which is to be called intermittent irrigation or flooding [11]. If this water management is practiced, water movement in the area would be accelerated, and it affects local hydrological regime.

4. Water management and water requirement of paddy fields

Water ponding in the fields requires much water. Water requirements of paddy fields compose mainly of transpiration of rice plant, evaporation from ponding water or soil surface, and percolation into soil profile. In some cases, requirement to reestablish water layer after intentional drainage and to implement flow-through irrigation for saving management labor or for

Paddy Fields as Artificial and Temporal Wetland http://dx.doi.org/10.5772/intechopen.80581 149

For planning and designing the irrigation facilities and the water use plan, water requirement is basically estimated base on evapotranspiration of rice field. The actual water lost in the field through other paths, including seepage into the deeper soil profile under the root zone part and run off or spill out into the drain through the field outlet, is often recognized as the "loss,"

Table 2 shows the total water requirements for one irrigation season reported by JSIDRE [12]. The total requirements range from 500 mm in Senegal to 3900 mm in Kazakhstan or 4500 mm in East Africa. This wide range is caused fundamentally by the significant difference in the seepage rates, which are estimated as none at minimum and more than 30 mm/day at maximum. The effects of water management on water requirements are to be regarded. Water requirement of paddy field in dry area is sometimes much and sometimes less than paddy field in the humid region. For example, as mentioned above, water requirement of paddy field in Egypt or Kazakhstan is relatively much, where consumption for evapotranspiration is large

with drier climate, while limited water availability constrains increased water use.

Table 2. Water requirement of paddy field per irrigation season [11].

4.1. Water requirements for paddy irrigation

control of temperature might be included.

rather than "requirement."
