6. Significance of paddy fields in the environment

#### 6.1. Paddy fields in local hydrological regime

Here, brief overviews of the cases of Egypt and Kazakhstan are introduced including the

Egypt is one of the typical countries that produce rice in dry area. It has a fast growing population with 82.5 million in 2011 leading to increased food demand. Almost all of water demand in Egypt is supplied by the Nile River, of which water is used extensively to irrigate crops including rice. Rice is one of the staple crops in Egypt and consumed 38.6 kg milled rice per person per year in 2009. Rice is grown in the summer on about 600,000 ha, mainly in the northern Nile Delta. The yield is quite high, about 9 t/ha in 2000, due to abundant solar energy

The area for rice is officially regulated by the government due to limited water resources, while farmers prefer cultivating rice for its higher profit. The areas for rice producing located in the northern Nile Delta have potential risk of soil salinization. Paddy cultivation has been functioning to leach out accumulated salts in the soil profile. Salt leaching in arable soils can be

In Kazakhstan, of which most of the land is classified as steppe or desert with annual average precipitation of 100–200 mm, wheat is a predominant crop in the northern part, whereas rice, cotton, fodder, and fruit are produced in the southern part in summer season. Its cropped area had increased due to rapid land reclamation mainly in the Syr Darya Basin since the 1950s to the 1980s, and the irrigated land became one of the big food supplying sources of the Soviet Union and Eastern Europe in that period. While rice occupies only 5–6% of the irrigated area, its water requirement is about 15% of the total irrigation requirement in that period. Most of the rice cropping area in Kazakhstan is distributed mainly in the Kzyl-Orda area of the Lower Syr Darya River Basin and some in the Ili River basin. The present total rice area is about 113,000 ha, which is equivalent to 17% of the total irrigated area. In the irrigated area in Kazakhstan, the crop rotation system is dominantly practiced with several rotation patterns,

In Kazakhstan, large-scale irrigated agriculture has been developed since the 1960s with crop rotation including rice. In the irrigation scheme, water is applied only to paddy fields, which consists about 30% of the total scheme, and paddy fields are continuously ponded. Basically upland crop is not irrigated directly, while water required in upland fields is supplied through much percolation from paddy fields. The efficiency of conveyance and distribution is quite low

Water requirement of paddy fields is around 3000 mm. Seepage from irrigation canals and deep percolation from paddy fields raise local groundwater table, and it functions as water source for upland fields surrounding the paddy fields. According to the study of the Tottori University Group, this water distribution system induces soil salinization (see [17]). In upland fields, salts accumulate during crop production with upwards water movement, while most of them are leached out when that field is cultivated with rice and flooded continuously for the

The large amount of water requirement for the large irrigation schemes, including much loss from the systems, needs much water diversion from the Syr Darya River, which is the main

supported by prevailing sub-surface drainage systems (e.g., [15, 16]).

and rice is grown usually in this crop rotation system.

due to not lined canals running through sandy soil.

rice growing season.

summary by GRiSP in the following [1].

and fertile alluvial soils.

152 Irrigation in Agroecosystems

Considering the limited availability of water resources, generally, it is reasonable to recognize that paddy cultivation in dry region is not realistic or acceptable in terms of sustainability of economics and environment in many cases. Actually, most of the paddy fields are developed in the humid region with much rainfall and much available water resources. It brings that paddy fields are suitable to humid condition. This is not wrong, while it simultaneously brings another question on significance of "suitability."

The Japanese paddy fields have been reclaimed and developed historically and recently improved much with large investments for advanced irrigation and drainage system (see [18]). With advanced farming techniques including the introduction of modern cultivars, nutrients, chemicals, machineries, and so on, they are proud of higher yield and productivity of rice production as well as the qualities. It needs, however, much lasting investments and labors to maintain the systems. They are always facing risks of flood and drought damages, and the cool and hot weather damages during rice growing season. There, the paddy fields and the system are maintained by everlasting human activities as hard as possible, which have developed the infrastructures, institutions, and interconnectedness in the society. This situation has been developed under the condition of climate and small-scale topography and river system, which are relatively controllable comparing with the continental conditions. Thinking over these history and present system, we can ask "Are the paddy fields in Japan suitable to its natural condition?" Some paddy fields in other regions can produce considerable yield without any hard investment, while its yield is not so high. This could be recognized as "naturally" suitable.

The point to be recognized here is just that the "suitability" of the paddy fields to the natural, and climate condition is not to be evaluated absolutely. It needs comprehensive conclusion, especially assessment in terms of sound hydrological cycle of the region or basin. Paddy cultivation and fields are to be arranged appropriately in the hydrological regime of the region. Then, consequently, we might find "suitable" and "sustainable" development of paddy fields in each region including dry area, which are to be located in right place in the local hydrological system.
