SEDIMENT TRAPPING BY TERRACED PADDY FIELD ON SLOPPING AGRICULTURAL LAND
<p>Terraced paddy field is not only important for rural food security,</p> <p>but also for trapping sediment in the slopping land. The aims</p> <p>of this research were to quantify the amount of incoming and</p> <p>outgoing sediments and to study sediment movement behavior</p> <p>during harrowing and fertilizing under traditional irrigation of</p> <p>terraced paddy field system. This study was carried out at Keji</p> <p>Village, Semarang District, Central Java during two cropping</p> <p>seasons, a wet season 2003/04 and a dry season 2004. A paddy</p> <p>field with eight terraces was selected. The terraces were flat,</p> <p>different in size and descending to the river. Sediment samples</p> <p>were taken at harrowing and fertilizing activities. The results</p> <p>indicated that at harrowing, outgoing sediment was higher than</p> <p>incoming both during the wet and the dry seasons. About 0.53</p> <p>and 0.27 t ha-1 day-1 of soil were eroded during harrowing in the</p> <p>wet and the dry seasons, respectively. However, a week before</p> <p>and after fertilizing, both in the wet and the dry seasons, the</p> <p>amounts of incoming sediment were higher than the outgoing</p> <p>one. In the wet season, the amounts of incoming sediments were</p> <p>three to four times higher than the outgoing one, both a week</p> <p>before and after fertilizing. During the wet season, about 0.31</p> <p>and 0.34 t ha-1 day-1 of sediment was yielded a week before and</p> <p>after fertilizing, respectively. During the dry season, the incoming</p> <p>sediments were ten times higher than the outgoing one.</p> <p>On an average the sediment yields were about 0.07 and 0.08 t</p> <p>ha-1 day-1 a week before and after fertilizing, respectively.</p> <p>Terraces having greater areas deposited more sediment than</p> <p>those with smaller sizes. During a week before and after first</p> <p>fertilizing, the total amounts of incoming sediments were 6.44</p> <p>and 1.19 t ha-1 for the wet and dry seasons, while that of</p> <p>outgoing sediments were 1.89 and 0.14 t ha-1 for the wet and dry</p> <p>seasons, respectively. This indicates that terraced paddy fields</p> <p>are not only producing rice, but also providing environmental</p> <p>service in term of sediment trapping. This external service</p> minimizes sedimentation in the downstream.