Acta Solum

Humic Acid and Nitrogen Fertilizer Effects on Nitrogen Availability and Bacterial Population in Sipramin-Affected Paddy Soil

Melinda Trisya Yulianto — 2026-06-01

The accumulation of sodium (Na) due to the continuous use of sipramin reduces the physical, chemical, and biological quality of soil, thereby affecting nitrogen (N) availability and microbial activity. This study aimed to evaluate the combined effect of humic acid and different nitrogen fertilizer sources on nitrogen availability (NH₄⁺ and NO₃^-) and bacterial population dynamics in sipramin-affected paddy soil. The experiment was conducted under greenhouse conditions using a completely randomized factorial design with two factors: humic acid doses (0, 20, 40, and 60 kg ha^-¹) and nitrogen fertilizer sources (NPK Phonska, urea, KNO₃, and MAP) at an equivalent rate of 92 kg N ha^-¹. Observations included NH₄⁺, NO₃^-, and total bacterial populations, and data were analyzed using analysis of variance (ANOVA). The results showed that the interaction between humic acid and nitrogen fertilizer did not significantly affect nitrogen availability. However, both factors individually showed significant effects on NO₃^- availability, indicating their role in influencing nitrogen dynamics. Bacterial populations increased from 7 to 21 Day After Treatment (DAT) and decreased at 42 DAT, reflecting temporal microbial dynamics during incubation. Although changes in bacterial populations coincided with variations in nitrogen forms, this relationship could not be directly confirmed due to the limitation of total culturable bacteria analysis. These findings highlight the importance of humic acid and nitrogen fertilizer management in regulating nitrogen dynamics under high-Na soil conditions, while further studies on specific microbial groups are needed to better understand the underlying mechanisms.

Geological Controls on Soil Shear Strength and Slope Instability in the Watugede Sub-Watershed

Vinni Lovita — 2026-06-27

Landslides are a common geomorphological hazard in tropical volcanic regions, particularly in areas with steep slopes and complex geological settings. Variations in soil properties on soil shear strength across different geological formations. This study investigated the physical and mechanical properties of soils developed from the Kebobutak, Semilir, and Nglanggeran Formations and evaluated their relationship with landslide susceptibility in the Watugede Sub-Watershed. Field surveys, geological observations, and soil sampling were conducted at landslide and non-landslide sites. Soil samples were collected from two depth intervals (0-30 cm and 30-60 cm) and analyzed for soil texture, maximum water content, plasticity index, clay sensitivity, cohesion, internal friction angle, and soil shear strength. A descriptive-comparative analysis was applied to assess differences among geological formations and slope conditions. The results indicate that landslide areas generally have higher moisture content and plasticity, accompanied by lower cohesion, internal friction angle, and shear strength than non-landslide areas. Soils derived from the Semilir Formation exhibited the greatest susceptibility to landslides due to their high water-retention capacity and relatively low shear resistance, whereas soils developed on the Nglanggeran Formation showed higher shear strength and greater slope stability. These findings demonstrate that geological formations play a significant role in controlling soil mechanical behavior and slope instability through their influence on soil physical and mechanical properties. The results provide a scientific basis for landslide susceptibility assessment, slope stability modeling, hazard mitigation strategies, and land-use planning in volcanic landscapes.

Assessment of Soil Degradation under Different Land Uses and Conservation-Based Management in Banjar Subdistrict, Buleleng Regency

Made Sri Sumarniasih — 2026-07-24

Land-use change and agricultural intensification in Banjar Subdistrict have the potential to degrade soil quality and disrupt biomass production. This study aimed to assess the potential, spatial distribution, and status of soil degradation under different land uses and to formulate conservation-based management strategies. The methods included field surveys, laboratory analyses, and spatial analysis using Geographic Information Systems (GIS) through overlay techniques of land use, soil type, slope, and rainfall maps. Soil samples were collected from 13 Homogeneous Land Units (HLUs) representing different land-use types and biophysical conditions. The results showed that moderate soil degradation potential dominated an area of 9,801.46 ha (85.55%), followed by high potential on steep slopes covering 1,026.02 ha (8.95%) and low potential in lowland areas covering 629.96 ha (5.50%). The soil degradation status was classified as light and distributed into three spatial units (R.I-p; R.I-p,f,a; R.I-p,v,a), with permeability, soil fraction, porosity, and pH as the main limiting factors. Recommended management practices include terracing, runoff control, cover cropping, organic matter application, crop rotation, and balanced fertilization.

Chemical Characteristics of Water Hyacinth Pellet Fertilizer with Different Adhesive Materials

Nukhak Nufita Sari — 2026-07-26

High application of inorganic fertilizers can negatively affect soil fertility and environmental sustainability. Organic farming uses organic materials to improve soil quality and support sustainable crop production. Water hyacinth (Eichhornia crassipes), an invasive aquatic weed, has potential as a raw material for pellet organic fertilizer. This study aimed to evaluate the chemical characteristics of water hyacinth pellet fertilizer using different adhesive materials in accordance with SNI 7763:2024 and to determine the most suitable adhesive material. The research was conducted using a descriptive-experimental method with three adhesive treatments: ET1 = water hyacinth flour + tapioca flour; ET2 = water hyacinth flour + wheat flour; and ET3 = water hyacinth flour + rice bran flour. Each treatment was repeated three times. All treatments used a ratio of 1:2:4 (water: water hygienist: adhesive). Chemical analyses included pH, organic C, total N, total P, total K, total macronutrients, and the C/N ratio. The results showed that pellet fertilizers with tapioca and wheat flour adhesives met the SNI standards for pH and organic C but did not meet the standards for total macronutrients and the C/N ratio. Pellet fertilizer with rice bran flour adhesive met the SNI standards for pH, organic C, and total macronutrients, although its C/N ratio exceeded the maximum standard limit. Rice bran adhesive also produced the highest total N, P, K, and total macronutrient contents among the treatments. Overall, rice bran flour was identified as the most suitable adhesive for improving the chemical quality of water hyacinth pellet fertilizer, in accordance with SNI 7763:2024.

Geomorphological Controls on Soil Fertility Across Potential Rice Expansion Areas in Tropical Lowlands

Bagus Adi Nugroho — 2026-07-28

Geomorphological variability strongly influences soil fertility conditions in tropical lowland environments and plays an important role in determining the potential for rice expansion. This study evaluated geomorphological controls on soil fertility across potential areas for rice expansion in Makroman, East Kalimantan, Indonesia, using a pedogeomorphic approach. Geomorphic units were delineated through visual interpretation of satellite imagery, field observations, and DEMNAS-derived elevation data. The study area was classified into four major geomorphic units: floodplains, undulating plains, rolling plains, and slopes. Soil fertility characteristics, including soil pH, soil organic carbon (SOC), and cation exchange capacity (CEC), were obtained from field-based soil observations and laboratory analyses across representative geomorphic units. The results revealed a clear fertility gradient across geomorphic units associated with dominant geomorphic processes. Floodplain environments exhibited the highest pH (5.8), SOC (1.7%), and CEC (32.4 cmol(+) kg⁻¹), whereas slopes showed lower pH (4.9), SOC (0.8%), and CEC (27.3 cmol(+) kg⁻¹). Intermediate conditions were observed in undulating and rolling plains, reflecting transitional redistribution and runoff-dominated processes. Depositional environments favored the accumulation of fine particles, organic matter, and exchangeable base cations, while erosional and leaching processes progressively reduced nutrient retention in elevated landscapes. These findings demonstrate that soil fertility variability in tropical lowlands is controlled not only by geomorphic position but also by the dominant geomorphic processes operating across the landscape. The study highlights the importance of geomorphology-based approaches for supporting sustainable rice expansion and land management in tropical agricultural environments.

Comparative Evaluation of Multispectral UAV-Derived Vegetation Indices in Rice Fields

Hana Hanifa — 2026-08-03

This study presents a comparative evaluation of multispectral UAV-derived vegetation indices (VIs) in rice fields. Seven UAV-derived VIs — the Chlorophyll Index (CI), Chlorophyll Vegetation Index (CVI), Modified Soil-Adjusted Vegetation Index (MSAVI), Green Normalized Difference Vegetation Index (GNDVI), Normalized Difference Red Edge Index (NDRE), Normalized Difference Vegetation Index (NDVI), and Perpendicular Vegetation Index (PVI) were computed from UAV multispectral orthomosaics acquired over a lowland rice field in Purwokerto, Central Java. The data were collected during the late vegetative stage of rice growth. Pearson correlation analysis showed strong positive correlations between the structural indices NDVI, MSAVI, and PVI (r > 0.93) and the chlorophyll-related indices CI and NDRE (r = 0.93), whereas CVI was negatively correlated with NDRE (r = −0.66), indicating that biomass accumulation and chlorophyll status did not always change together. Forty-three field points, classified into rice condition categories, were used to train and test a Random Forest classifier. Both models reached the same overall test accuracy of 63.64% (Kappa = 0.42 and 0.41, respectively), and the cross-validated model reached a cross-validation Kappa of 0.48 at mtry = 7. Variable importance ranked PVI as by far the most influential predictor (importance = 100), followed at a distance by CI (18.4), NDRE (12.9), and CVI (9.5), while MSAVI, NDVI, and GNDVI contributed little. Soil-background-sensitive PVI carried the strongest discriminative signal, chlorophyll-related indices added complementary information, and GNDVI was largely redundant. These findings offer preliminary evidence that PVI, paired with CI or NDRE, is the most relevant index combination for UAV-based rice field assessment.

Combined Basal and Foliar NPK Fertilization Effects on Soil Properties and Rice Production

Shiamita Kusuma Dewi — 2026-08-04

Rice (Oryza sativa L.) productivity in intensively cultivated paddy systems is limited by soil fertility loss and low nutrient use efficiency of conventional NPK fertilization, which is prone to ammonia volatilization, leaching, and phosphorus fixation in tropical soils. Foliar NPK application is proposed to bypass soil nutrient losses and improve fertilizer efficiency, but its combined effects with basal fertilizer on soil properties and rice production in tropical paddy conditions are poorly understood. This study aimed to evaluate the effects of combined basal and foliar NPK fertilization on selected soil properties and rice production under tropical paddy conditions in Central Lampung. A field experiment was conducted using a Randomized Complete Block Design with 8 treatments and 4 replications, comprising combinations of basal and foliar NPK. Soil properties, including pH, soil dispersion ratio, and soil texture, alongside agronomic parameters, were associated with rice production. The results showed that combined basal and foliar NPK application significantly affected soil pH, with treatment H having a higher soil pH than the control and the standardized fertilizer. Combined application also significantly improved rice agronomic performance, with treatment H recording the highest rice production of 4.23 kg plot⁻¹, representing a 50% increase over the control treatment. These findings show that combining basal and foliar NPK fertilization can potentially manage nutrients to sustain soil fertility and enhance rice production in tropical paddy systems.

Integrated Land Degradation Assessment through Geographic Information Systems and Soil Biophysical Evaluation in Kalibeluk Village, Batang Regency

Farchan Mushaf Al Ramadhani — 2026-08-15

Land degradation is a major environmental issue that reduces soil productivity and impairs ecological functions. Kalibeluk Village, Batang Regency, has diverse biophysical characteristics that may result in varying levels of land degradation. This study assessed land degradation potential and the corresponding degradation status in Kalibeluk Village, using GIS-based spatial analysis supported by field verification and laboratory assessment. Spatial analysis was conducted using soil type, slope gradient, rainfall, and land use parameters through an overlay technique to determine land degradation potential. Field verification and laboratory analyses were subsequently performed for each Land Mapping Unit (LMU) to evaluate land degradation status based on Government Regulation of the Republic of Indonesia Number 150 of 2000 and Regulation of the State Minister of Environment Number 07 of 2006. The results classified land degradation potential into three categories: low (71.481 ha; 39.8%), moderate (104.167 ha; 57.9%), and high (4.137 ha; 2.3%). Evaluation of land degradation status indicated that LMUs with low and moderate degradation potential were categorized as Slightly Degraded (R.I), whereas LMUs with high degradation potential were categorized as Moderately Degraded (R.II). The main limiting factors were soil fraction composition, water permeability, redox conditions, and surface rockiness. The findings demonstrate that GIS is an effective tool for identifying land degradation levels and supporting land management planning. Recommended rehabilitation measures include agroforestry, cover crops, terracing, the application of organic matter and soil amendments, and conservation drainage systems to improve soil quality and reduce land degradation risks sustainably.