The study is a bibliometric analysis, a mathematical and statistical mapping of academic activity rather than a laboratory experiment. The researchers systematically searched the Web of Science database using the descriptors biochar, bio-char, biological charcoal, or agrichar in combination with sandy soil, then filtered the results to articles and review articles. That search yielded 543 publications spanning 1992 to 2024, with records from 2025 excluded because indexing was still incomplete. The corpus was then processed with two dedicated tools: VOSviewer version 1.6.18, which built co-authorship, citation, and keyword co-occurrence networks using thresholds of five minimum documents and five minimum citations, and the Bibliometrix extension version 3.0 in R, which generated rankings, three-field plots, and thematic clusters using the Walktrap algorithm and multiple correspondence analysis.

The temporal picture is dramatic. The first publication in the field appeared in 1992, in the journal Geoderma, and has since accumulated roughly 2,443 citations. Yet for years the topic barely registered: only four articles were recorded up to 2010, and no publications at all appeared between 1993 and 2006. In 2011 the annual count doubled to eight, and after 2015 the field entered genuine exponential growth, peaking in 2021 with 73 publications registered for that year. The authors caution that apparent fluctuations after 2021 likely reflect delays in database indexing rather than a real decline in research activity. What the curve captures is the consolidation of biochar as a mainstream strategy for soil conditioning, driven by its dual promise of agricultural improvement and climate change mitigation through carbon sequestration.

Geographically, the analysis reveals a field with clear power centers. China leads in publication volume and sits at the center of the international collaboration network, maintaining exchanges with Brazil, Germany, the United States, Canada, and Egypt. The United States and Germany rank as the next most prolific contributors. Intriguingly, when citations are normalized by output, Germany leads the impact ranking, indicating higher average influence per paper. At the institutional level, the Chinese Academy of Sciences tops productivity with eighteen articles, alongside the University of Florida and Assiut University, but smaller institutions such as Tottori University, Kangwon National University, and University College Dublin outperform them on citations per article. Among individual authors, Amin Abu El-Eyuoon Abu Zied leads productivity with twelve papers, while researchers like Gao Bin, with an average of 164 citations per article, and Ok Yong Sik, with 133, demonstrate that influence and volume do not always coincide.

The most cited works cluster between 2010 and 2016, the period when the field matured, and together they define the scientific agenda. Yao and colleagues tested thirteen biochar types for retention of nitrate, ammonium, and phosphate in sandy soil and found that most had little or no capacity to sorb nitrate and phosphate, while nine effectively removed ammonium, a result underscoring that performance depends on both the biochar and the nutrient in question. Abel and coauthors, in the field’s most cited paper with 546 citations, showed that biochar and hydrochar applied at 1, 2.5, and 5 percent by weight reduced bulk density, increased total pore volume, and raised water content at the permanent wilting point, expanding available water capacity except in highly humic soils. Uzoma’s team demonstrated that cattle manure biochar, rich in essential nutrients, boosted maize productivity in sandy conditions, while Kammann and colleagues found that biochar enhanced quinoa growth, water- and nitrogen-use efficiency, and drought tolerance even under moderate water stress.

Not every result is a success story, and the review is candid about the contradictions. Jeffery and colleagues conducted field experiments in the Netherlands with herbaceous-feedstock biochars and found no significant improvement in water retention, aggregate stability, or hydraulic conductivity despite the chars’ high porosity and internal connectivity, concluding that hydrophobicity must be considered alongside porous structure. Namgay’s work showed that activated wood biochar can significantly reduce plant availability of arsenic, cadmium, copper, lead, and zinc in maize, pointing to a remediation role, while Haefele’s rice husk biochar increased soil organic carbon, nitrogen, phosphorus, and potassium availability but showed little pH effect and, notably, some carbon migration to deeper soil layers in sandy profiles. Schulz and Glaser found that compost alone outperformed biochar-compost combinations for oat yields in infertile tropical sandy soil, a reminder that biochar works best as part of integrated nutrient management rather than as a standalone fix.

Thematic mapping of the literature reveals where the intellectual energy lies. Environmental Sciences dominates with 38 percent of publications, or 207 of the 543 articles, encompassing carbon sequestration, contamination mitigation, and biogeochemical cycling. Soil Science follows at 32 percent with 174 publications focused on structure, porosity, pH, and water-holding capacity, while Agronomy and Plant Sciences account for 19 and 16 percent respectively. Keyword clustering identified five thematic groups: soil physical properties such as hydraulic conductivity and water holding capacity; chemical aspects including cation exchange capacity and ammonium; sustainability and greenhouse gas emissions; contaminant sorption, mobility, and desorption; and residue-derived biochars for heavy metal remediation. The term biochar itself is the most recurrent keyword with 316 occurrences and a total link strength of 2,150, followed by sandy soil with 129 occurrences, confirming the field’s tight focus.

Beneath the statistics, the review also synthesizes the technical fundamentals that determine whether biochar helps or disappoints. Feedstock is decisive: lignocellulosic residues such as coconut shells, sugarcane bagasse, rice straw, bamboo, and wood are favored because their high carbon content and structure favor water and nutrient retention, while manure-based and waste-derived materials such as sewage sludge are gaining attention for their nutrient richness. Pyrolysis temperature shapes the product, with chars made around 600 degrees Celsius tending toward greater porosity and surface area that enhance water retention in sandy profiles. Heating rate and residence time matter too: slower heating maximizes biochar yield and produces more stable carbon structures, while longer residence times raise fixed carbon content, pH, and surface area at the cost of yield. Because alkaline chars from materials like coconut shells and rice straw can also correct soil acidity and improve phosphorus availability, matching production parameters to target soil problems is emerging as a core engineering challenge.

The overall verdict from three decades of literature is that biochar is a genuinely promising strategy for sandy soils, particularly through enhanced water retention, improved nutrient dynamics, and reduced leaching, with added potential to immobilize toxic trace elements and stabilize erodible aggregates. But the variability in reported outcomes, driven by feedstock, pyrolysis conditions, application rate, and edaphoclimatic context, means there is no universal prescription. The authors identify clear gaps: long-term field validation, regional adaptability, and standardization of feedstock selection and application rates all remain underdeveloped. Their roadmap calls for extended field experiments across diverse climates, standardized production protocols, and integration of biochar with other sustainable soil management practices, including exploration of its role in climate change mitigation. For a material that began as little more than charcoal rebranded, biochar’s trajectory from a single 1992 paper to a 543-article global research enterprise suggests that the scientific community sees in it something durable: a way to make the world’s thirstiest soils hold onto water, nutrients, and carbon at the same time.

Subject of Research: Bibliometric analysis of global research trends on biochar application to sandy soils

Article Title: Bibliometric analysis of global research trends in biochar application to sandy soils

Article References: de Paiva, F. D. C. A., de Assis Freire, J. V., de Sousa Antunes, L. F., Fernandes, G. M., Alves, A. B., Bezerra, H. N., de Morais Rosária, P. C., de Medeiros, C. C., de Souza, D. C. S., de Oliveira, E. K. G., & da Silva, P. P. (2026). Bibliometric analysis of global research trends in biochar application to sandy soils. Discover Soil, 3(1), Article 105. https://doi.org/10.1007/s44378-026-00270-5

Image Credits: AI Generated

DOI: 10.1007/s44378-026-00270-5

Keywords: biochar, sandy soils, bibliometrics, pyrolysis, water retention, nutrient leaching, soil fertility, carbon sequestration, soil remediation, feedstock, Web of Science, sustainable agriculture

The findings, published in the Journal of Agriculture and Food Research, carry serious implications for how growers interpret soil tests, not just in Florida but anywhere crops are grown on phosphorus-enriched soils. Florida’s potato industry is substantial, with roughly 6,800 hectares harvested in 2023 producing 190,500 megagrams of tubers valued at 105.4 million dollars. Because potato plants have shallow root systems, limited root hairs, and a notoriously weak ability to scavenge phosphorus from soil, the crop is heavily dependent on fertilizer inputs. Decades of repeated applications have left many fields with elevated soil-test phosphorus values, well above the thresholds where guidelines say no additional fertilizer is needed.

Yet growers in the region have repeatedly reported yield losses when they withheld phosphorus in high-testing soils. To investigate, the research team ran a factorial experiment over three growing seasons at the UF/IFAS Hastings Agricultural Extension Center. Two adjacent 0.3-hectare sites were planted with the chipping cultivar Atlantic each spring from 2023 to 2025. The sites shared a soil type, a sandy Alfisol of the Ellzey series, but differed sharply in their starting phosphorus status. Site 1 averaged 50.6 milligrams per kilogram of Mehlich-1 extractable phosphorus in the surface 15 centimeters, while site 2 averaged 110.9 milligrams per kilogram. Under the historical interpretation system, both values fall into the high or very high categories, which normally trigger no phosphorus recommendation at all.

Each site received ten treatment combinations: five phosphorus pentoxide rates, from zero up to 269 kilograms per hectare, crossed with two nitrogen rates of 168 and 280 kilograms per hectare. The team tracked soil phosphorus and mineral nitrogen through the profile, measured plant biomass and nutrient uptake at 50, 70, and 90 days after planting, and mechanically harvested and graded tubers according to USDA size classes. A total of 240 plot-level observations across six site-years fed into the analysis.

The results were striking. At site 1, the field with the lower starting phosphorus, fertilization raised total yield from 21.6 megagrams per hectare in the unfertilized control to an average of 30.6 megagrams across rates of 135 to 269 kilograms of phosphorus pentoxide per hectare, a gain of roughly 42 percent. Marketable yield climbed even more dramatically, from 16.4 to about 25.1 megagrams per hectare, an increase of 53 percent. Most of the gain came from intermediate-sized tubers, the A23 fraction, which jumped from 9.1 to 17.4 megagrams per hectare. Tuber specific gravity, a key quality measure for chipping potatoes, also improved. At site 2, by contrast, phosphorus rate had no significant effect on total yield, marketable yield, tuber size distribution, or specific gravity, and the yield gap between the two sites vanished once phosphorus was applied at 135 kilograms per hectare or more.

The physiological story behind those numbers is revealing. At site 1, phosphorus fertilization increased whole-plant dry biomass from 5.48 to 7.96 megagrams per hectare and nitrogen uptake from 89.5 to 132.2 kilograms per hectare, while nitrogen uptake efficiency rose from 26.8 to 42.3 percent. In other words, when phosphorus is limiting, the constraint ripples outward: restricted root and shoot growth lower the plant’s demand for nitrogen and its capacity to acquire it. Adequate phosphorus supply therefore unlocks the crop’s ability to use nitrogen efficiently. At site 2, the higher-phosphorus field, the only response to added fertilizer was a modest increase in nitrogen uptake efficiency, with biomass and productivity per unit of nitrogen unchanged. Notably, whole-plant phosphorus uptake at site 2 pulled ahead of site 1 after 50 days after planting and stayed ahead through harvest, showing that the richer soil sustained phosphorus delivery during the critical tuber-bulking period.

Nitrogen management, meanwhile, turned out to be a non-player in the phosphorus story. The two nitrogen rates produced clearly different soil mineral nitrogen levels, but phosphorus rate by nitrogen rate interactions were limited to efficiency indices, and the crop’s principal responses to phosphorus were identical under both nitrogen regimes. Raising nitrogen from 168 to 280 kilograms per hectare never increased yield and consistently reduced both nitrogen uptake efficiency and partial factor productivity, the tubers produced per kilogram of nitrogen applied. In the difficult 2024 season, when seed-piece decay cut plant stands by 57 percent, the higher nitrogen rate actually lowered total and marketable yields by about 4.4 megagrams per hectare. The team stresses this does not establish 168 kilograms as a regional optimum, only that extra nitrogen neither overcame phosphorus deficiency nor added yield when phosphorus was sufficient.

The soil itself told a story of accumulation and movement. Over the experiment, surface Mehlich-1 phosphorus in fertilized plots rose by roughly 63 to 67 milligrams per kilogram, while unfertilized controls declined by 7 to 27. Concentrations peaked near crop emergence after pre-plant fertilization and then shifted, with measurable increases detectable down to the 30 to 45 centimeter layer, particularly at site 2 in 2024. Because most potato roots in these seepage-irrigated soils sit within the top 30 centimeters, phosphorus moving below that depth is effectively out of reach for the crop and represents a potential pathway for transport off-site, although drainage losses were not directly measured in this study.

To translate the yield responses into a usable threshold, the researchers modeled relative yield against Mehlich-1 phosphorus measured at harvest using four normalization methods and several calibration models. The best-performing combination, the MAXRATE normalization paired with a modified arcsine-log model, explained 41 percent of the variation in relative yield. It estimated critical phosphorus levels of 63.6 milligrams per kilogram for 80 percent relative yield, 81.4 for 90 percent, and 96.2 for 95 percent, with the response curve flattening above roughly 100 milligrams per kilogram. Those numbers are far above the historical sufficiency threshold of about 30 milligrams per kilogram of Mehlich-1 phosphorus, and they even exceed the high category boundaries of both the Mehlich-1 and Mehlich-3 systems currently used in Florida. The moderate fit and the overlap of high- and low-yielding observations across the range reinforce a point echoed in decades of Ohio fertilizer trials: a soil test is a probabilistic index of potentially available phosphorus, not a deterministic boundary between deficiency and sufficiency.

The practical message is nuanced. A high soil-test classification does not guarantee a field will ignore added phosphorus, and skipping fertilizer in a responsive high-testing soil can be costly; conversely, blanket phosphorus applications to nonresponsive soils simply inflate soil phosphorus reserves and environmental risk. The authors caution that their critical level of 96.2 milligrams per kilogram derives from a specific soil, cultivar, sampling protocol, and set of conditions, and that each initial phosphorus status was represented by a single site with different irrigation infrastructure, so broader calibration and independent validation are needed before any new threshold enters recommendations. Still, the study makes a compelling case that Florida’s provisional allowance of up to 134 kilograms of phosphorus pentoxide per hectare, applied regardless of soil test, is a blunt instrument. A validated critical level could enable a tiered strategy: full fertilization below the threshold, crop-removal-based maintenance near it, and deliberate drawdown above it, protecting both potato yields and the waterways downstream of phosphorus-enriched sands.

Subject of Research: Potato yield and nutrient uptake responses to phosphorus fertilization in phosphorus-enriched sandy soils

Article Title: Initial soil phosphorus status governs potato yield and nutrient uptake responses to fertilization in P-enriched sandy soils

Article References: Oliveira, J. D. M., de Castro, G. F., da Silva, B. A., Clark, M. W., Nunez, G. H., Guzmán, S., & Zotarelli, L. (2026). Initial soil phosphorus status governs potato yield and nutrient uptake responses to fertilization in P-enriched sandy soils. Journal of Agriculture and Food Research, 31, Article 103296. https://doi.org/10.1016/j.jafr.2026.103296

Image Credits: AI Generated

DOI: 10.1016/j.jafr.2026.103296

Keywords: phosphorus, potato, soil testing, Mehlich-1, fertilizer recommendations, sandy soils, nitrogen use efficiency, critical phosphorus level, Florida agriculture, nutrient uptake, soil fertility, alfisols