• Abstract and Figures
• Public Full-text

熱 帯 農 業(Japan・J.Trop.Agr.)27(4):244-258,1983 Land Use Strategy in Tropical River Basin from the Viewpoint of Soil Conservation* -Watershed Management in Lampung Province , Indonesia- Masahiko TOMITA**, Masaru TOYOTA***, Hajime TAKENAKA**, Mitsukata SuzuKI****, K. E. S. MANIK***** and B. ROSADI***** **Faculty of Agriculture , The University of Tokyo, Tokyo 113 ***Faculty of Agriculture , Niigata University, Niigata 950-21 ****Institzcte of Agricultural Engineering , University of Tsukuba, Sakuramura Nihari-gun, Ibaraki 305 *****Fuculty of Agriculture , University of Lampung, Province Lampung, Indonesia Abstract Significant developments of Lampung agriculture have been caused by the artificial improvements of regiomal ecosystems due to the recent large-scale hydrological construction. But the agriculture at the region is so stable and sometimes suffers drastic damage because these artificial improvements have not yet been accustomed to the nature and human life of the region. So, after some consideration on regional agro-ecosystem and present condition of watershed, a simula tion model for watershed management was developed and adapted to the Seputih river basin. It is resulted that in order to maintain the stability of regional agriculture and hydro-facilities some improvement should be made as written in Section 5. The rivers flowing through Lampung carry many suspended soil particles which eventually enter canals as sediment and close water passages. Rainfall is the first agent to produce soil erosion which makes river water turbid. Therefore, appropriate management of watershed is essential for the conser vation or the improvement of regional agro-ecosystem. 1. Agro-Ecosystem in the Province of Lam season, so that dry farming exceled in traditional pung agriculture. These are the typical characteristics (1) Geographical aspect of Lampung Pro of tropical area. vince (2) Agriculture in Lampung Province of Lampung is located in far south There are 430, 000 ha of dry farms (for rubber, part of Sumatra Island. Micro-landf rom of south- coconut, palm, coffee, clove, pepper, cassava, etc.) ern part of the Sumatra, is divided into 4 types, and 260,000 ha of paddy fields in Lampung i, e., mountain, peneplain, river and coastal plain today. However more 490,000 ha of primeval according to Kaida,1) and the central greater forest are lying for the objects of agricultural part of Province of Lampung belongs to the development besides 300, 000ha of reserved forest peneplain in this classif iccation. A heavy rainfall and 340, 000 ha forestry-use area.2 around 1, 900 to 3, 200 mm per year erodes the ) The agricultural development in Lampung can accumulation of volcanic ash soils and contributes be divided into three stages. Stage I is before to shape micro-landf orm. Large rivers flowing the 18th century, and upland cultivations of through Lampung, Way Seputih, Way Sekam- kapok, banana, cassava, cereals and rice prevailed pung and Way Tulangbawang, originate from under shifting cultivation. Stage II is the 19th the Barisan mountains and flow down eastwards century, and shifting cultivation prevailed in most through the peneplain and coastal plain to the parts of the peneplain, while coffee, pepper and Java sea. Annual rainfall of Lampung is enough rubber plantations were newly developed. Stage for rice planting, but most of it occur in wet III is the 20th century, then goverment promo- * Received 22 December 1982 . ted transmigration to Lampung and constructed TOMITA et al.: Land Use Strategy in Tropical River Basin from the Viewpoint of Soil Conservation 245 Tabe 1 Basin land use and SS of river water tion). The harvesting area of Lampung are shown in Table 1. The area of paddy field (under waterlogged conditions) dominates, but is still small in comparision with the total paddy area of the Indonesia. The other main crops of Lampung are upland rice, cassava, coffee, clove, pepper and soybean. National policy and economy impact the agri- cultural development of a country. But, one of the direct factors of the agriculture develop- ment is environmental conditions for the plant growth. Plant growht is affected by light, fertil- ity of soil, and water. From the viewpoint of hydrology, either excess or shortage of water influences plant growth and agricultural develop- ment. The typical conditions and land use of excess and shortage of water in Lampung are * no data as land use map , but it eeems that about 10% of catchment is used for dry farming in ac- as follows ; cording to observaiion, (i) Excess of water results in waterlogged ** sub-basin No . equal to Block No. in Tank Model conditions. The sites under these conditions are, Simulation e. g., humid lowlands of the central Way Jepara, the river mouth of Way Seputih, and the alluvial irrigation systems for settlements, one of which site of the Barito river in Kalimantan. Farm was the huge irrigation canaal of Way Sekam- lands hardly exist in these sites because there pung which was constructed in 1935. exist no drainage canals except the Way Jepara In 1977, the total population of Lampung short-cut. reached 3.7 million (2.8 % of the total popula- (ii) In Tropical region it has considerable tion) and the population in rural villages was rainfall around 2,000 mm in the wet season but 3.1 million (85 % of the total Lampung popula- not so much in the dry season. The shortage Table 2 Type of irrigation system for lowland rice fields in Lampunp 246 熱 帯 農 業27(4)1983 of water in the dry season restricts the Lampung of irrigation system agriculture. In the scant rainfall area, they chose Every plant species repeats its growth cycle drought resistant crops such as cassava that is in each generation. The accumulated biomass of generally grown in the peneplain. Other crops a plant species increases as the succession ad- which require more rainfall like tea are grown vances, but the regrowth of the species declines on the hill and mountain slopes which are gradually and finally ceases completely, which favored with rainfall. In spite of the shortage is called •gclimax plant growth•h from the view- of water both farmers and national economy point of succession. When the generation reaches require rice production in paddy fields. An the climax condition, it is called climax ecosys- irrigation system is then a prime tool for this tem. And, when the first generation is repeated purpose. And, the planning of an irrigation by artificial harvesting, it is called agro-ecosys- system depends basically on the location of the tem. Naturally, agro-ecosystem produces a new water sources available. Because Lampung lo- biomass increment in each generation which cates in the peneplain and can not gather enough climax ecosystem does not. In extensive concept, rain water within its catchment area, water the elements involved in the agro-ecosystem are should be carried through canals from the out- crops cultivation and social conditions such as side. Therefore, the development of canal net- economy, policy and human organization. The works also results in the agricultural develop- relation between these elements in the agro- ment. ecosystem of Lampung was studied according to According to the whole Lampung survey of the approach of R. P. Hart.3) And the ecosystem hydrological condition and its support engine- of farm lands as an subsystem in such system ering of paddy field, irrigation systems for the is shown in detail in Fig. 1. This is an agro- paddy fields in Lampung are classified into the ecosystem in limited or physical concept. As to following seven types ; I, II, IIIa, Tub, IVa, IVb the above discussion, the relation between agro- and V (Table 2). ecosystem and social conditions outside is shown The construction cost of each type increases in Fig. 2. The described relation helps to under- from I to V and the stability of water supply stand the meaning of an irrigation system in the is also improved correspondingly. Therefore the agro-ecosystem in limited concept. The condition types from I to V give an index of the agricul- of a new irrigation system causes an increase tural development from the viewpoint of water in farm land area. And, the improvement of an use stability. And the major type of paddy existing system increases the productivity of fields found in Lampung is IVb because of farm land. This is the reason why the big irri- recent large irrigation projects. gation system constructions are basic in agricul- Agricultural development depends largely on tural development. But excessive increase in reasonably managed irrigation systems. But the population may cause forced land clearing and examples obtained in Lampung suggest the fol- consequently affects the homeostasis of environ- lowing two problems, One in the lack of ex- mental ecosystems. Therefore, the number of perience. Irrigation types of IVa, IVb and with settlers must be limited to a permissive level. artificial canals are still very rare and most of And in the paddy fields with irrigation types the farmers have not experienced the manage- of I to IIIa, a stable agro-ecosystem in a limited ment of organized and advanced irrigation sys- concept prevails while its productivity is on a tems, The other one is the difficulty in mobili- low level. On the other hand, in the fields with zation. The transmigrated populations have irrigation types of VIb and V, advanced types, originated from various regions. This fact hinders the following problems seem to be unavoidable. communication and cooperation among farmers One problem is that these fields are derived which are necessary for the management of from poor soils such as podzols and latosols, so irrigation systems. that sufficient fertilizers may be required for These problems are probably common among local varieties too. Another one problem is that most developing countries and should be solved.

Load more

  15

Copy Link