Volcanic activity produces pyroclastic deposits when erupted and cover the surrounding area. The minerals contained in these deposits are the source of plant nutrients. The volcanic deposits weathered, release nutrients to the environment, and improve soil chemical properties. The eruption of Mt. Sinabung in 2018 covered an area of 30, 320 ha, while in 2019 was 1, 371 ha. The study aims to investigate the status of nutrient content and the volcanic ash weathering level in 2020. There were 16 samples taken from ash deposits at various depths, with a total area of 1, 585.31 ha. Samples were analyzed to determine the total elemental composition using X-ray fluorescence (XRF) spectrometer, nutrient reserves, and weathering indices. The results showed that the total elemental composition of SiO2 is 51.51-67.51% classified as mafic (basalt) to felsic (dacite) materials, Al2O3; 15.54-23.41%, Fe2O3; 2.84-10.02% and CaO; 3.94-6.46%. Mount Sinabung’s volcanic ash has a nutrient reserve capacity of MgO, CaO, P2O5, K2O, and SO3, respectively with the amount of 37, 384.17 kg/ha, 235, 794.99 kg/ha, 34, 293.12 kg/ha, 72, 357.39 kg/ha, and 70, 352.22 kg/ha. The weathering indices of volcanic ash of 2020 were determined with a value of 2.76-4.19 for Ruxton ratio and Product of Weathering Index (PWI) of 67.39-76.13, indicates the weathering rate of silicates from volcanic ash are still at initial stage and are still in the fresh condition.

Psament is a soil that has a low fertility rate which is characterized by low organic matter content (BO) so there are less water and nutrients available. Utilization of Psament for agricultural development must first be improved through other inputs such as BO and lime. This study aims to look at the interaction between KOJETO types and KOJETO doses on the chemical properties of Psament, to look at the effect of KOJETO types on the chemical properties of Psament, and to look at the effect of increasing KOJETO doses on the chemical properties of Psament.

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.

Regosol has low fertility, especially carbon (C), nitrogen (N), phosphorus (P), potassium (K) and other macro elements, but it can be potential for agriculture cultivation. Addition of straw compost and tithonia granule (Kojeto granule) with clay binder can improve chemical soil fertility. This study aimed to determine the composition of the Kojeto granule with a clay binder and to define the interaction between type of Kojeto granule and dosage of compost granule in the chemical characteristics of Regosol. This research was conducted in a wirehouse and soil laboratory, Andalas University. The experiment used a completely randomized factorial design, with two factors and three replications. The first factor was the ratio between compost composition and clay binder 9:1 and 8:2. The second factor was 4 levels of granule compost doses (0; 7,5; 15; 22,5 t ha-1). The results showed that the best composition ratio between Kojeto and clay binder on chemical properties was 9:1. The type of Kojeto 8:2 and dosage (22 t ha-1) had an interaction on Ca-dd (3.75 me 100 g-1). The single effect on the type compost granule at type 9:1 was parameter C-org (2.23%), and single effect on increasing the dosage of granule compost at a dose of 15 t ha-1 was C-org (2.30%), N-tot (0.27%), P-available (14,30 ppm), pH (5,80), and K-dd (0.62 me 100 g-1). The optimal recommended dose is 15 t ha-1.

The low level of soil fertility resulted in a decrease in productivity intensification of rice fields. One of the efforts conducted by farmers to improve fertility is the continuous application of synthetic fertilizer (PS). Intensive use made PS cause pollution and soil damage. This study was aimed to identification at the best combination the straw plus tithonia compost (J+T) and biochar to improve soil chemical properties intensification of rice fields, and then looked the effect of increasing compost (J+T) and biochar to soil chemical properties intensification of rice fields. This research was conducted in rice fields in Kuranji, Padang City, West Sumatera. The experimental design used a randomized complete block design. The treatments were 0% compost (J+T) and 0% biochar; 100% compost (J+T); 75% compost (J+T) and 25% biochar; 50% compost (J+T) and 50% biochar; 25% compost (J+T) and 75% biochar; 100% biochar. The results showed that the 25% compost (J+T) and 75% biochar was the best combination to improve soil chemical properties intensification of rice fields. The dosage increased soil pH by 6.30; Eh 65.00 mV; organic C 2.53%; organic M 4.35%; total N 0.93%; available P 26.00 ppm; CEC 40,48 cmol kg-1; exchangeable K 1.47 cmol kg-1; exchangeable Ca 1.06 cmol kg-1; exchangeable Na 0.67 cmol kg-1; and exchangeable Mg 0.57 cmol kg-1.