Study on the growth of Agathis sp. in a coffee plantation in East Kalimantan (Indonesia)

This trial was carried out on a farmer shifting cultivation land. This land was first cleared for cultivation in 1980. It was later planted with maize. As the maize was 1 1/2 months old, coffee was planted between the rows. After the second rotation, in 1981, maize was not productive any more, and planting of other tree crops and woody plants like Parkia speciosa, Gliricidia sepium and others began. A cash income of US $ 67 was obtained from selling maize in 1980 and 1981. Coffee yields varied from US $ 150 to 250 per year, starting 1984 until 1988. Additional income the range of US $100 to 200 per year was created, from 1988 on, by selling petai (Parkia speciosa) beans. Two hundred and fifty Agathis sp., trees were planted, in 1988 between the coffee bushes. The growth of Agathis was measured for 5 months in 1988/89. The average height increment during this period was 29 cm, average diameter growth 4.5 mm. Height and diameter growth varied depending on the degree of slopes: of 20-40 percent inclimation, height growth was 15 cm and diameter growth 2.9 cm, while on 5-10 percent slopes and on land with an inclination of less than 5 percent, height growth was 29 and 44 cm, diameter growth 4.6 and 5.3 mm, respectively. The plants have received 1290 mm of precipitation and an average irradiation intensity of 945 Umol s-5 1/10m 1/20, or 86 percent of the value observed above canopy during the five months of measurement. Results showed that edaphic site conditions, particularly slope degree, are more decisive for the growth of Agathis than irradiation. Only plants which grew less than 20 cm in height, during the study, had received considerably low irradiation. Especially irradiation in the morning, when water stress is not yet limiting photosynthesis, influenced growth considerably. A follow-up study is required to fully understand the mutual interactions of the combination of two plants like Agathis and coffee, especially at a time when Agathis figures more prominently in the radiation and nutrient budget of the site.