A brief history of early soil investigations by Dutch researchers in Sumatra, shaping the birth of tropical soil science.
Deli is a region in the East coast of Sumatra famous for its tobacco. The plantation industry in Deli was started in 1863 by a Dutch colonial planter. After several years of trials, the soils of Deli produced high-quality, broad, thin yet strong light-coloured leaves for cigar wrap that were highly demanded in Europe and the USA.
It was often quoted that the fertile soils between the Wampu and UIar rivers in Deli produced these fine quality tobacco. In addition, it has a suitable climate with rainfall that is quite uniform throughout the year and the availability of cheap labor (known as contract coolie).
The East Coast of Sumatra was known as a cultuurgebied (plantation belt). European planters flocked to East Sumatra to establish tobacco plantations. The Deli area soon ran out of soil, and planters began to open up areas to the west and north of Deli in the Asahan and Batu Bara areas.
In 1890, the East coast of Sumatra (Deli, Padang Bedagai, Serdang, Landkat, Batu Bara, Labuhan Batu & Asahan afdeeling) had established a total of 232 estates/companies with a total of 426,000 hectares of land concession.
The colonial planters cleared a large swath of virgin forests in Deli and found out that the soil was different and had low fertility. Lands with the same forest cover, but the soils are completely different. A lot of them were disappointed by the low quality of the tobacco. They blamed the rain or the sunshine that favoured one area over the other. Some blamed that the managers or the neighbour must have had better luck.
As shown in the map of tobacco plantations below (in dots), the expansion started in late 1880 throughout the northwest and southeast region of Deli. From 1920 onwards, the plantations shrunk back to the original Deli area as they found out the soils are not suitable.
The real reason was soil, which took them a long time to appreciate. Initially, the colonial planters recognised only three soil types in Deli: grayish white soil from the coastal plain, red soil at higher elevations, and randomly spotted black soil. The geology of the Deli area is unknown, it was only assumed that the soils came from nearby volcanoes.
Dutch planters began to ask researchers from the Botanic garden in Buitnezorg (Bogor) for help. In 1895, Melchior Treub (1851–1910), the Director of the Lands Plantentuin (Botanic Garden) in Buitenzorg, established a contract to conduct scientific studies specifically on Deli tobacco culture.
Since soil science does not exist yet at that time, soil research was done by chemists. The first chemist was Dr. A. van Bijlert, appointed to work on soils of Deli in 1897.
The chemists analysed thousands of soil samples to work out the best fertiliser application. But they still cannot determine which soils would be good and bad for tobacco. They made more measurements, soil pH was thought to be the master variable, followed by soil texture, and so on. They still cannot tell where and how the soils are distributed. Maps were produced, but the results are incomprehensible.
Another group of researchers called themselves agrogeologists believed that “In the beginning was the rock and the rock is the mother of the soil”. Knowing the mother of soil would be crucial.
Julius Mohr, a chemist from the Botanic garden, founded the Laboratorium voor Agrogeologie en Grondonderzoek or the Agrogeologeology department in 1905 to gain new knowledge of soils. Mohr demonstrated that the soils from acidic liparite tuff from Siantar are completely different from soils derived from basic andesite deposits of Java. He established the principles of soil survey based on agrogeology.
The failures of mapping by chemists who worked on soil samples, instead of looking at the soil in the field, made the Deli research station established the agrogeological department in 1926 in charge of soil mapping. Christiaan Hendrik Oostingh (1889–1940) was in charge and made the first attempt by recognising three main volcanic materials: rhyolitic (acid, less fertile), dacitic (intermediate), and andecitic (basic, most fertile).
In 1929, Jan Henri Druif (1893–1970) took over the investigations and started surveying and taking many samples of rocks and soils from all over Sumatra’s east coast. The soil samples were examined for mineralogical composition to determine which rock they came from.
Finally, Druif made a breakthrough by recognising the distribution of different volcanic materials in which the soils were formed. Subsequently, he can make detailed soil descriptions of Deli in his four-part publication: De Bodem van Deli or the Soils of Deli (1932, 1934, 1938, and 1939).
Druif concluded that the area of Deli had at least five different volcanic deposits. The most dominant one is the rhyolitic tuffs (hardened volcanic ash ejected during a volcanic eruption) from the Toba super eruption 74,000 years ago. These tuffs are acid and poor in nutrients. Subsequent eruptions from Mount Sibayak and Sinabung produced two types of dacitic tuffs, and there were also a couple of lahars. The first event produced a dacitic-rhyolitic tuff on the country’s western part. And subsequently, an andesitic lahar from Sinabung gives the so-called black dust soil, which is very fertile.
The oldest soils can be found in the northwestern hill (Langkat) region, derived from the Tertiary sedimentary rocks. As the soils were less affected by recent volcanoes, they were poor in nutrients, acid, and deemed unsuitable for tobacco.
Druif further divided the soils of Deli into those formed by the in situ weathering of the tuffs and the soil materials that were carried and redeposited by the rivers.
The Deli Research Station compiled the historical price of tobacco estates in the Deli and demonstrated that the soil type is related to the tobacco’s price. Soils derived from rhyolitic tuff fetched the lowest price while the alluvials from dacitic materials and black dust soils worth the most.
After almost 40 years of trials, the Deli tobacco planters finally had a complete description of the soil. In 1935, Druif completed a 1:100,000 agrogeological (soil) map of the Deli area based on a geological-morphological-mineralogical approach.
However, it was a bit late as the industry had already shrunk and 7 years later, the Japanese arrived.
The soil map was not further explored and used after that, as now soil science moved towards using a classification scheme made at national and international levels.