Abstract
Low prices of rubber has been a serious problem to rubber smallholders in Indonesia. Rubber-based intercropping systems offers a practical solution to this issue and increasing overall productivity of intercrops, for example upland rice and maize. This study reviewed the suitable spatial arrangements in rubber planting to long term impact based intercropping systems. A field experiment was established in a smallholder rubber plantation in Tanah Laut Regency, South Kalimantan with area of 50 ha. Two planting patterns of rubber PB 260 clone were tested: (1) single row planting pattern (SR) by 6 m x 3 m, and (2) double row planting pattern (DR) by 18 m x 2 m x 2.5 m. The experiment showed that girth of rubber trees in the SR system at the first tapping year was slightly larger than in DR system, even though statistically it was not significant. The latex yield per tree of SR and DR systems were similar, however, latex yield per hectare of SR system was higher than DR system due to a higher tree population in SR system. The DR system was technically suitable for long term intercropping, because when rubber tree can reached 8 to 9 years old and light penetration was more than 80% at distance from the rubber row. The total area required for rubber, upland rice and maize grown in monoculture to produce an equivalent of a one hectare of rubber-upland rice-maize intercrop is 1.87. This means the intercropping has an advantage compared to monoculture.
Highlights
Rubber is an important commodity in Indonesia, especially in Sumatra and Kalimantan
The average light penetration in the center of the single row planting pattern (SR) system is 22.35 (Figure 4) and in the narrow row of the double row planting pattern (DR) system is 15.6% (Figure 5). This means that the light penetration is not more than 30% at each point measured on the SR system
The DR system is more suitable for long term rubber based intercropping
Summary
Rubber is an important commodity in Indonesia, especially in Sumatra and Kalimantan. Farmers choose rubber as main crop because it is easy to grow, yield can be stored for long period, rubber can be grown in low fertility soil, and provide daily income [1]. Indonesia farmers plant rubber using single row with a planting distance of 6 m x 3 m (550 trees / ha), or 7 m x 3 m (476 trees / ha) [1, 6, 10]. Under these planting system, intercrops can only be planted until rubber plants are 1 to 2 years old [18, 6, 7, 10], as the canopies of adjacent rows would have closed and the light is light intensity under the canopy would only be 50-60% [19, 20]. Double plant spacing will allow more sunlight to intercept between rubber row [6, 21, 22]
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