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.

Polluted irrigation can degrade soil chemical properties and then decrease land productivity. This research aimed to compare the effectiveness of biochar against manure in reducing the concentration of some heavy metals(HM) in the polluted rice field. This pot trial was conducted at Glasshouse using two types of amelioration (biochar and manure). Biochar and manure were incubated with paddy soil under field capacity at the glasshouse for one month. The results showed that increasing the dosage of either biochar or manure applied decreased the availability of HM, especially Fe (r=-0.87, r=-0.89) and Mn (r=-0.82, r=-0.91), respectively. However, there was no effect of biochar (r=0.25) but increased by manure (r=0.95) application on Zn concentration. Furthermore, some other heavy metals concentration also decreased, such as Ag (r=-0.89), Pb (r=-0.54), Cu (r=-0.51), Cr (=- 0.50), and Ni (r=-0.64) by applying biochar but tended to increase by applying manure. Both biochar and manure could increase some plant nutrients, especially K (r=0.74, r=0.82), P (r=0.85, r=-0.44), Mg (r=0.98, r=0.91) and Ca (r=0.98, r=0.84), respectively.

Volcanic ash material (Vam) can cover the surface of the farming land post volcano eruption. The covering process could be advantageous for soil fertility if it is thin enough, but it can be destructive for the crops if it is thick. The purpose of this research was to study the effect of the application of Geo-organo granules from volcanic ash and Tithonia (Tt) for the production of Baby Corn in Oxisol. The pot experiments design with six treatments (1AV:1Tt; 1AV:2Tt; 1AV:3Tt; 1AV:4Tt; 1AV:0Tt; 0AV:1Tt)) three replications, and used Completely Randomized Design (CRD). The criteria test of compost standard used to test the benefit of these Geo-organo materials (PT Pusri, SNI, and Regulation from Agriculture Ministry, Republic of Indonesia). Corn growth was also measured for height and yield. Plant height and yield were analyzed using F-test and continued using HSD at a 5% level of significance. The results showed that Geo-organo granules be to improve soil chemical properties of Oxisol, and mass of cob of Baby corn.

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.

The increasing of Indonesian population has led to a decrease in the area of rice fields in Indonesia. Therefore, it is needed to increase the fertility and the productivity of paddy soil. Since 1984, several attempts have been made to increase the productivity of paddy soils through the green revolution program, but this has had a negative effect on the fertility of paddy soils. The exploitation of paddy soil layers which has been increasing for years has decreased paddy soil. Other aspects of paddy soil management need to be done; one of them is a mixture of top soil layer with plow pan layer. The mixture of top soil layer with the plow pan layer is expected to improve the soil fertility. This research was conducted with the aim to study the effect of the top soil layer and plow pan layer on the chemical properties of paddy soil. This study used a completely randomized design with five treatments of mixing paddy soil layers and three replications. The treatments were A1 = 100% top soil layer, A2 = 75% top soil layer + 25% plow pan layer, A3 = 50% top soil layer + 50% plow pan layer, A4 = 25% top soil layer + 75% plow pan layer, and A5 = 100% plow pan layer. The results showed that the A2 treatment gave changes in optimal soil chemical properties. The A2 treatment decreased EH value to 133 mV, increased pH to 6.08, organic-C 2.22%, total N 0.30%, available P 27.94%, CEC 38.50%, exchangeable Ca 0.88 me 100g-1 , exchangeable Mg 0.37%, exchangeable K 0.94% and exchangeable Nadd 0.17%.