The Indonesian transmigration program is one of the largest organized resettlement efforts in the world.
Since 1905, successive Governments have sponsored the migration of poor farmers from the overcrowded islands of Java and Bali to
relatively under-utilized neighboring islands, particularly Sumatra. The soils of the region were classified as Red-Yellow Podzolics
(Ultisols under USA soil classification). The soils were almost uniformly highly acidic with a median pH of 4.5-4.7.
Regarding plant nutrients, they are deficient in nitrogen, extremely deficient in phosphorus and possibly low in potassium.
Aluminum toxicity was a potential for upland food crop production. The main ecological threats to be avoided were soil erosion,
deterioration of soil fertility and structure, increases in pests and diseases, and possible reductions in wildlife.
And grasslands in general were covered with alang-alang in the area.
In addition, transmigrants preferred rice and cassava as their staple foods indicating that cassava-based cropping pattern including rice cultivation should be introduced in this area.
Therefore, the objectives of this study were to establish the cassava- and rice-based cropping patterns,
to control alng-alng from the viewpoints of family economics and soil fertility,
to elucidate the efficiency of the application of animal manure, green manure and liming, and to control the soil erosion by cropping pattern in the transmigration areas in south Sumatra.
Furthermore, among staple crops, cassava most abundantly absorbs K, suggesting that a nutrient disorder might occur among the intercrops.
Therefore, to evaluate the growth of crops and the fate of N fertilizer with reference to the application of K in a cassava-based cropping system,
the field experiment was conducted. The results obtained were as follows:
| 1) |
The relatively higher income and calorie production were obtained in the cropping pattern which consisted of
(upland rice (Oryza sativa L.) + corn (Zea mays L.) + cassava) / peanut (Arachis hypogaea L.) / cowpea (Vigna sinensis Endl.)
(first / second / third crop seasons, respectively). |
| 2) |
Minimum (strip tillage) or no tillage produced yields of all crops similar to or better than conventional cultivation
(full tillage) in 1979/80 crop season both in Batumarta and in Way Abung. Net return evaluation showed that zero tillage and
minimum tillage systems produced more profits than full tillage system both in Batumarta and in Way Abung in 1979/80 crop season.
Better return was also obtained by zero tillage and minimum tillage systems in Way Abung study site in 1980/81 crop season. |
| 3) |
The results showed that yields of all crops increased by the application of animal manure and green manure in combination with NPK fertilizers.
The yield of all crops increased along with the duration of organic manure application during the years of experiment. On the contrary,
the crop yields in the treatment with NPK fertilizers only tended to decrease from year to year.
Application of lime with 1.1 or 2.2 ton/ha/year in this experiment increased crop yields to the levels obtained by manure application. |
| 4) |
The amount of eroded soil during the first 4-month period in the rainy season was about 90 % of the annual amount.
Cassava cultivation with intercropping of upland rice and maize as the first intercrop reduced the amount of soil erosion.
Soil erosion decreased appreciably from year to year. |
| 5) |
Cassava intercropped with upland rice and maize followed by peanut or soybean was suitable from the viewpoints of crop yield
and maintenance of soil fertility in upland areas of Red-yellow Podzolic soils. |
| 6) |
The dry weight and yield of cassava, upland rice and corn without K application were lower than those with K application treatment.
The recovery rate of basal N by upland rice and cassava was positively related to the yield of each crop. Amount of immobilized N
in soil applied to upland rice was not affected by the application rate of K. |
| 7) |
Total recovery rate of basal N applied to upland rice was 2 times higher in the K application treatment than without K application treatment,
suggesting that K application alleviated the N pollution problem by inducing a higher uptake rate of N fertilizer by crops. |
Finally, author recommends following cropping pattern:
(upland rice (Oryza sativa L.) + corn (Zea mays L.) + cassava (Manihot esculenta Crantz)) / peanut (Arachis hypogaea L.) /
cowpea (Vigna sinensis Endl.)).
インドネシアでは、1905年以来政府の方針によりジャワ島等の人口密度の高い地帯からスマトラ島、カリマンタン島等の人口密度の低い地帯への移住政策が採られてきた。
移住先であるスマトラ島は、赤黄色ポドソル土壌に分類され、酸性が強く、低肥沃土地帯である。また、土壌浸食、雑草（alng-alng）も問題となる。移住者はライスイーターといわれるほど米を好む。
そのため、キャッサバを含む作付け体系が一般的と考えられている。そこで本研究では、キャッサバ、陸稲を中心とした作付け体系の確立、alng-alngへの対処法、土壌肥沃度の改善のための有機物施用、
土壌浸食防止を目的とした。さらに、キャッサバがカリを特異的に吸収することから、カリ施用と施肥窒素の挙動の関係を検討した。得られた結果は以下の通りです。
| 1) |
作付け体系を経済的収入及びカロリー生産からみた場合以下の作付け体系がもっとも優れていた。
（陸稲＋トウモロコシ＋キャッサバ）／落花生／ささげ(１期作／２期作／３期作) |
| 2) |
不耕起ないし最小限の耕起での収量は普通耕起と差が認められなかった。また、純収入を考えると不耕起ないし最小限の耕起が優れていた。 |
| 3) |
有機物と化学肥料の併用によって、収量が増加した。一方、化学肥料の単用は収量を減少させる傾向が認められた。また、石灰の施用も重要であることが示された。 |
| 4) |
雨期の始まりの４月間に土壌浸食全体の90%が発生していた。キャッサバの間作に陸稲ないしトウモロコシを植え付けることによって、土壌浸食を軽減することが可能であった。 |
| 5) |
キャッサバの間作に陸稲ないしトウモロコシを植え付け、その後に落花生ないし大豆の作付け体系は、土壌肥沃性の維持と収量という観点から優れているものと考えられた。 |
| 6) |
カリ肥料なしで栽培するとキャッサバ、陸稲、トウモロコシの収量、バイオマス生産は減少した。また、基肥窒素のキャッサバと陸稲による利用効率も減少した。しかし基肥窒素の有機化量はカリ肥料の有無に関わらずほぼ一定であった。 |
| 7) |
カリ肥料を施用した場合の基肥窒素の回収率は無施肥に比べて約２倍であった。この結果は、窒素の環境汚染という観点からも重要である。 |
最終的に、
（陸稲＋トウモロコシ＋キャッサバ）／落花生／ささげ(１期作／２期作／３期作）という作付け体系がスマトラ南部の地帯ではもっとも適しているものと考えられた。
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