Water and Soil Management for Water Conservation in a Watershed - Water and Agriculture: Sustainability, Markets and Policies - page 292

activity in OECD. Therefore, it is very important to study on WRC in arable lands
beneficial to the prevention of damages due to heavy rains during summer season in
Korea, having paddy rice as the predominant crop.

Table 1. Change in land use (area: ha)

Cultivated land

Year Total Forest (%) Others (%)

Paddy field (%) Upland (%)

1990 9,927,369 1,345,280(13.5) 763,532(7.7) 6,476,030(65.3) 1,342,527(13.5)

1995 9,926,838 1,205,867(12.1) 779,390(7.9) 6,451,885(64.9) 1,489,696(15.1)

2000 9,946,074 1,149,041(11.6) 739,724(7.4) 6,422,128(64.6) 1,635,181(16.4)

2004 9,961,738 1,114,950(11.2) 720,684(7.2) 6,400,301(64.2) 1,725,803(17.3)

Source : Ministry of Government Administration and Home, Ministry of Agriculture and Forestry, Forestry Administration, 2005.

Water in soil was separated into water (Wi) coming into underground soil from rain
or irrigation and water (Wo) above the soil surface. The Wi and Wo of paddy fields and
non-paddy fields such as upland, grassland, and orchard were calculated by using two
different methods. One was a 'water balance' method and the other a 'water rechargeable
pore space' method. The results are shown in Table 2 (Jung et al. 2002). Rice paddy
fields had much smaller WRC in the soil than above the soil surface under flooding
conditions during the months from June through September, when torrential rains occur.
But the WRC in non-paddy fields was larger in-soil than above the soil surface.

Arable land area, as mentioned earlier has decreased as a result of the expanded
market opening for agricultural products, and the growth of the other industries except for
agricultural sector. Thus, the reduction of cultivated land has influenced the WRC of
agricultural land as in Figure 2, which shows the change in WRCs of agricultural land
with a change in arable land area. WRC reached the peak in the latter half of 1980s, and it
has been decreased since then. It implies that the potential risk of flooding increases with
the reduction in WRC. Actually, damage by storms and floods at a similar precipitation
level were observed to be greater since the early 1990s, with paddy land diminishing.

Table 2. The WRC by land use type in 2000
(million tons)

WRC
(Wi+Wo)

Land use Wi Wo

Paddy field - 2,378.4 2,378.4

Upland 353.4 214.9 568.3

Grassland 60.1 110.0 170.1

Orchard 123.5 113.2 236.8

Total 537.0 2,816.5 3,353.5

Sources: ASI, 1986 and 1991; NIAST, 2000 and 2002; MAF, 2002.