Soil organic carbon [OC] sequestration is affected by some factors, one of which is the vegetation living on it. Tea is a crop on which the part being harvested is the leaves, which are supposed to contribute to soil OC. The objective of the research was to determine the amount of OC sequestered at different crop age under tea plantation in wet tropical areas. The soil samples were taken from 3 different crop ages [36, 21, and 9 years old] under the same slope [>45%] and soil [volcanic] at ≥ 1,400 m asl. As a comparison, the soil was also sampled from the secondary forest around the research site. At each crop age and the forest, the soil was sampled for 100 cm depth with a 20 cm increment. Undisturbed soil samples were taken for soil BD and disturbed soil samples for OC. The result showed that SOC content decreased by soil depth, and the soil BD was not significantly different among the depths. Therefore, the amount of OC sequestered declined by decreasing soil depth. The SOC sequestration rate decreased by increasing the age of tea crop from 1.67 to 0.49 Mg/Ha/y/1-m depth respectively between 9-21 and 21-36 years old. Compared to the secondary forest, however, the OC sequestration under tea plantation improved by 1.50, 1.71, and 1.79 times as the age of tea crop increased from 9, to 21, and to 36 years old, respectively. It seems that tea cultivation is the potential to sequester OC even though the leaves are regularly harvested.

Open mining causes some problems to the soil properties both in situ and ex situ or in the environment. A research on the effect of gold mining on physical properties of Inceptisols was conducted in Nagari Muaro, District of Sijunjung West Sumatra Indonesia. The disturbed and undisturbed soil was sampled at the ex gold mining, and at the previous land use, especially rubber plantation and grassland. Parameters analysed were soil texture, bulk density (BD), hydraulic conductivity (HC), soil organic matter (SOM), soil aggregate stability (SAS), and water content. Based on laboratory analyses, it was found that gold mining process changed soil physical properties at the top 0-40 cm soil in Muaro Sijunjung. It decreased SOM content, soil HC, SAS index, TP, and increased soil BD or hardness compared to the previous land use. The soil must be rehabilitated to increase its productivity and to anticipate environmental pollution.

The primary constraint of suboptimal soils under wet tropical regions, besides their low pH, is their low soil organic matter (SOM) content. This research was aimed to determine SOM stock of suboptimal soil orders (Ultisol, Oxisol, and Inceptisol) under corn (Zea mays) cultivation. This research was conducted using survey method, and soil samples were taken from 0-20 cm soil depth from each soil order under two types of land use (LU), corn cultivation and forest, in Lima Puluh Kota Regency, West Sumatra, Indonesia. The soil samples were analyzed at the soil laboratory at Andalas University, Padang. Parameters analyzed were soil bulk density (BD), texture, SOC, total-N. Data resulted showed that the soil texture from the three soil orders was classified as clay loam to clay, with the sand size particle was Inceptisol >Oxisol>Ultisol. Then, soil BD was categorized as medium. The highest SOM stock was at Oxisol under forest LU, then Ultisol and Inceptisol. Generally, SOM stock under forest was higher than under corn LU except at Ultisol, which the SOM stock was comparable. SOM stock under corn cultivation reached 43.7%, 87.7%, and 102.8% of that under forest, respectively, for Inceptisol, Oxisol, and Ultisol. Approximately 52-89% of the SOM was in the form of particulate organic matter (POM). The percentage of POM was generally higher under corn cultivation than that under forest LU. Stock soil total-N under corn cultivation compared to under forest was 37.7%, 68.7%, and 90.9% for Inceptisol, Oxisol, and Ultisol, respectively. The C/N ratio value of the SOM was considered medium.

Organic carbon (OC) is an important factor for soil and the environment. This research aimed to identify OC sequestration under different age of gambier crops in central Gambier, Pesisir Selatan, West Sumatra. Soil samples were taken from different crop ages ( 2, 5, and 10 years old), and then under secondary forest nearby as a comparison at 0-30 cm soil depth. The results showed that, in general, soil OC content was considered low to very low either under Gambier crops (<2%), or under forest land use (2.11%). Then, the OC stock increased by increasing crop age from 2 to 10 years old. The OC stock at ten years old Gambier reached 90% of that at the forest on the top 30 cm soil depths. Rate of OC sequestration was approximately 1.03 Mg ha-1 y-1 and 4.88 Mg ha-1 y-1, respectively, for crop age between 2 and 5 as well as between 5 and10 years old. This low soil organic carbon (SOC) content combined with fine soil particles caused the soil had medium-high soil BD, low-medium total soil porosity, rather slow-medium hydraulic conductivity rate, and unstable-rather stable soil aggregate stability. The study concludes that SOC sequestration under Gambier plantation in the sloping area was quite slow, especially during the first five years due to new crop establishment and the leaves harvested.

Maninjau Village, including the tourist destination of Buya Hamka in Sungai Batang, is susceptible to natural disasters, such as landslides. It happens due to the sloping and high rainfall (> 3000 mm per year) area. The soil is prone to landslides if the sloping land is intensively cultivated for crop growth. This community engagement activity socialised and practised alley cropping techniques to manage farming in the sloping area. This method for introducing the alley cropping technique was through presentation and discussion as well as practice in the field with a farming group “Sehati”, a member of KPGH (Hamka generation youth community), and community leaders of the Nagari Sungai Batang in November 2021. A farmer cultivating red onion adopted the alley cropping method for the farm having a 19o39’ (36%) slope level with an alley width was 5 m. Gliricidia sepium and Tithonia diversifolia, known as green manure crops, were placed perpendicular to the slope of the alley fence. Gliricidia was planted every 5 m, and Tithonia between the Gliricidia at a 0.2 m distance in the alley fence.