Taek-Keun Oh

Biochar application is widely proposed to improve crop yield and fertilizer productivity, yet its performance varies across climatic, soil, and management contexts. This global meta–analysis study of about 705 database entries retrieved from 93 studies analyzed responses across climatic classification, biochar feedstock and properties, soil properties, fertilizer and co–application regimes, and experimental types. Overall, biochar responded at 33%, 34%, and 32% for yield, PFPN, and PFPP. The strongest response occurred at the tropical, humid agro–ecological zone under moderate temperature regimes. Wood-derived biochar with lower pyrolysis temperatures (200 kg ha) showed reduced response. Economic benefit analysis also showed the average overall highest maximum yield at ≤40–80 t ha^–1 biochar rates demonstrating simultaneous improvement in yield and fertilizer productivity under appropriate management.

For efficient microplastic (MP) separation, there is a need to remove the soil organic matter (SOM), which interferes with MP extraction. However, the efficient SOM removal strategy from agricultural soils remain under debate. Therefore, this study investigated the SOM decomposition efficiency and MP recovery yield under varying environmental temperatures (i.e., 0, 20, and 40℃) conditions using five different removal solutions in three types of agricultural soil (i.e., upland, orchard, and greenhouse soils). Considering the thermal sensitivity and characteristics of MP samples, the study aimed to identify pre-treatment conditions that effectively decompose SOM content without significantly compromising MP recovery yield. Soil samples containing 1% (w/w) polystyrene (PS) particles were subjected to distilled water, acid-digestion (HNO 3), alkaline-digestion (KOH), and oxidative (H 2 O 2 and Fenton [H 2 O 2 + FeSO 4 ]) treatments, followed by density-separation using NaCl solution (1.21 g•cm-3), and the PS recovery rate was quantified after oven-drying. The SOM decomposition accelerated with increasing environmental temperature, and the its highest efficiency, which reduced SOM content by 44, 36, and 29%, were observed in the Fenton reagent-applied upland, orchard, and greenhouse soils, respectively. The MP recovery rates were positively correlated with SOM decomposition efficiency, and the oxidation reaction consistently yielded higher MP recovery yield than other approaches. However, the H 2 O 2 treatment led to variable MP losses, particularly in low-organic soils, suggesting possible MP degradation during excessive oxidation. Hence, treating agricultural soil with the Fenton reagent at 40℃ condition was found to be the most effective strategy for decomposing SOM content while maintaining MP integrity.

This study evaluated the effects of rice husk biochar (pH 11.0) application on soil properties and Kimchi cabbage (Brassica rapa L. cv. Hwanggeumbaechu) yield under different soil pH conditions. Three soil types, including acidic (pH 3.92), neutral (pH 6.59), and alkaline (pH 8.31), were prepared by adjusting an initial upland soil with 0.1 M hydrochloric acid (HCl) or 0.1 M sodium hydroxide (NaOH), while maintaining other chemical properties constant. Rice husk biochar was applied at 1% (w/w) and compared to an inorganic fertilizer application solely. Biochar application significantly increased soil pH, electrical conductivity (EC), total nitrogen (T-N), organic matter (OM), available phosphorus (Avail. P), and exchangeable Ca 2+ , with the greatest improvements observed in neutral (pH 6.59) upland soils. Kimchi cabbage showed superior uptake performance of the soil NH 4 + , NO 3-, and Avail. P contents in ranging from pH 6.3 to 6.5, declining under excessive soil alkalinity. Biochar treatment enhanced cabbage yield across all pH conditions, with the highest yield (32.28 Mg•ha-1) in neutral soils, indicating 13% greater than the alkaline counterpart. Nutrient use efficiency (NUE) patterns varied: N and P 2 O 5 uptake decreased with increasing pH beyond neutral, whereas K 2 O uptake increased under alkaline conditions. These findings indicate that rice husk biochar can improve soil fertility and crop productivity, but its effectiveness depends on initial soil pH. Overly alkaline conditions may reduce the benefits by lowering N and P availability despite improved K uptake. Therefore, soil pH assessment should precede biochar application to maximize agronomic and soil improvement effects.

Biochar has gained significant attention due to its ability to improve soil quality, reduce carbon emissions and improve crop yield. The use of only conventional fertilizer is not the way to sustainable agriculture, but the combined use with biochar can improve soil fertility and enhance nutrient uptake. This study used different biochar levels consisting of B0 (0% biochar, 0 g•pot-1); B1 (100% biochar, 4 g•pot-1); B2 (200% biochar, 8 g•pot-1) each combined with nitrogen-based fertilizer (urea and slow releasing fertilizer [SRF]) applied as F1 and F2 respectively under greenhouse environment during the winter season. The data were taken 100 and 121 days after transplanting (DAT). The overall results shows that 200% biochar with urea (B2F1) had a significant influence on plant height, grain dry weight, total chlorophyll, and nitrogen use efficiency (NUE) of about 30%, 200%, 100%, 95% respectively in both Mibaek #2 and Taeyangchal. These findings give a comparable understanding of the physiological growth, grain yield, and enhanced NUE in corn production.

The application of biochar combined with organic fertilizers is increasingly being recognized as a sustainable strategy for improving soil quality and crop productivity. Ginkgo leaves are abundantly generated but rarely utilized because of their allelopathic effects and poor degradability. In this study, the allelopathic activity of ginkgo leaf biochar produced at three different pyrolysis temperatures (300 °C, 500 °C, and 700 °C) was evaluated through seed germination tests using six species of seeds—three crops (kale, lettuce, and perennial ryegrass) and three weeds (annual bluegrass, barnyard millet, and slender amaranth). Additionally, the effects of organic fertilizer mixed with different ratios (10% and 30%) of ginkgo leaf biochar on soil chemistry and lettuce growth were also evaluated. Seed germination assays revealed that biochar produced at 300 °C and 700 °C inhibited germination in most species, while biochar produced at 500 °C showed no allelopathic effects on any of the tested species and promoted germination in lettuce and kale. Soil chemical properties indicated that application of organic fertilizer mixed with ginkgo leaf biochar increased soil pH, total carbon, and total nitrogen content. Notably, soil total nitrogen content increased with higher pyrolysis temperatures and mixing ratios of ginkgo leaf biochar. In lettuce growth trials, organic fertilizers mixed with biochar produced at temperatures above 500 °C significantly increased the fresh weight, leaf length, leaf width, and leaf number of lettuce. Applying organic fertilizer mixed with 30% biochar produced at 500 °C increased fresh weight by 63.6% relative to the control (organic fertilizer without biochar). Ginkgo leaf biochar produced at moderate temperatures (around 500 °C) and applied at higher ratios effectively enhanced crop growth, promoted germination, and improved soil fertility. These results suggest that this approach can promote the recycling of biomass and contribute to sustainable agricultural productivity.

Reclaimed agricultural soils, which accounts for 7.1% (112,464 ha) of Korea's agricultural land, is increasingly required to support upland crop cultivation amid national efforts to enhance grain self-sufficiency. However, both low-fertility and high-salinity of these soils significantly hinder crop productivity. This study aimed to assess the physicochemical properties of reclaimed agricultural soils from 69 locations in the Saemangeum reclaimed area to provide foundational documents for improving upland crop productivity. Soil samples were collected in 10 cm increments down to a 70 cm depth and analyzed for bulk density, moisture content, porosity, pH, electrical conductivity (EC), and exchangeable cations (i.e., K + , Ca 2+ , Mg 2+ , and Na +) content. The averaged bulk density (1.44 g•cm-3) and porosity (45.76%) at a depth of 0-30 cm met the appropriate range for upland crop cultivation, although localized compaction requires attention. Gravimetric and volumetric moisture contents exceeded the optimal standard, ranging from 20 to 25%, suggesting the need for periodic monitoring. Soil pH and EC values increased with the deepening of soil depth but generally remained within sustainable ranges (pH, 6.0-7.0; EC, ≤ 2.0 dS•m-1). However, the Saemangeum reclaimed agricultural soils had the excessive K + and Mg 2+ concentrations and insufficient Ca 2+ level, which may impair crop productivity. These findings highlight the necessity of targeted soil amelioration strategies, especially Ca 2+ supplementation and Na + mitigation, for sustainable crop cultivation in reclaimed agricultural soils.