1 Introduction

Soil fertility dynamics are central to the sustainability of intensive vegetable systems, where short growth cycles and high input use can rapidly alter nutrient pools and biological functioning. In many greenhouse and open-field systems, nutrient surpluses of nitrogen (N), phosphorus (P), and potassium (K) drive soil acidification, salinization, and imbalanced nutrient ratios, ultimately threatening long-term productivity and environmental quality (Fan et al., 2020). Within this context, radish (Raphanus sativus L.) offers a useful model for examining soil nutrient changes during cultivation because of its rapid growth, high nutrient demand, and sensitivity to fertilization strategies that simultaneously affect yield, quality, and soil health (Jin et al., 2024).

Radish is a widely grown root vegetable with substantial economic and nutritional importance, cultivated from tropical to temperate regions and ranking among the major vegetable crops in countries such as China and Pakistan (Yousaf et al., 2021; Gautam et al., 2025). Beyond fresh root consumption, radish contributes to food and feed systems in multiple forms, including large Asian radishes, oilseed types, and small European forms, and also serves as a cover crop and green manure that improves soil physical properties and supports subsequent crops (Hereshko et al., 2021). Global germplasm collections encompassing thousands of accessions underscore the crop’s genetic and phenotypic diversity, supporting breeding for improved root quality, stress tolerance, and adaptation across diverse agroecological zones (Kurina et al., 2021).

In root vegetable production, soil nutrient dynamics directly influence root growth, architecture, and quality traits. Meta-analysis across arable crops shows that N and P deficiencies reduce root biomass and length but often increase root length per unit shoot biomass and root-to-shoot ratios, reflecting plastic adjustments to low nutrient availability (López et al., 2023). At the cropping-system scale, imbalanced fertilization and continuous cultivation can accelerate losses of organic matter and microbial activity, while integrated nutrient management (combining mineral fertilizers with organic amendments) enhances root development, nutrient use efficiency, and maintains positive NPK balances in vegetable rotations (Sharma et al., 2023). For radish, studies combining reduced mineral N with organic or bio-organic fertilizers consistently report higher yields and improved quality alongside increases in soil organic matter, total N and P, and beneficial microbial groups, indicating strong coupling between fertilization practices, soil nutrient status, and plant performance (Jin et al., 2024; Qi et al., 2025).

Despite these advances, important gaps remain in understanding soil nutrient changes specifically during radish cultivation. Many radish studies emphasize yield and root quality responses to single or combined nutrient inputs, while providing only end-point soil measurements, making it difficult to reconstruct intra-seasonal nutrient dynamics or link shifts in enzyme activities and microbial communities with N, P, and K turnover. Long-term radish monoculture research has documented changes in soil pH, enzyme activities, and microbial community composition without large shifts in organic carbon, suggesting that biological indicators may respond faster than bulk nutrient stocks, yet these responses are rarely quantified alongside detailed nutrient budgets or balance calculations. Furthermore, broader analyses of nutrient imbalances in intensive vegetable systems highlight severe NPK surpluses and associated degradation, but often do not resolve crop-specific patterns or short-cycle dynamics characteristic of radish. Therefore, the present study focuses on soil nutrient changes during radish cultivation, aiming to quantify temporal shifts in key soil nutrient pools under contrasting fertilization regimes, relate these changes to radish growth and yield responses, and provide process-oriented insights that can inform nutrient management strategies for sustainable, high-quality radish production.

2 Baseline Soil Nutrient Characteristics before Radish Cultivation

2.1 Soil physical and chemical properties under different land uses

Baseline soil conditions for radish depend strongly on previous land use, which shapes bulk density, porosity, and nutrient-holding capacity. In the Tarai region of Uttarakhand, bulk density in the surface 0-15 cm layer ranged from 1.15-1.44 Mg/m³ and porosity from 45.9%-56.0%, with legume-based and diversified cereal systems showing better physical properties and water‐holding capacity than vegetable-based, orchard, or uncultivated land, indicating improved soil structure where diverse root systems and organic inputs are present (Lohani et al., 2025). Similar depth-wise assessments in eastern Uttar Pradesh showed that soil pH, EC, organic carbon, and available N, P, and K varied significantly among rice-wheat, legume‐based, vegetable-based, plantation, forest, and barren lands, underscoring that radish may be established on soils with very different starting physical and nutrient regimes depending on prior use (Pandey et al., 2023).

Chemical fertility baselines also differ among land uses, with implications for initial radish nutrient availability. In Myanmar research fields, topsoil (0-20 cm) under cereal-legume and cereal-based systems was moderately acidic (pH 5.37-6.15) with low CEC (4.81-5.88 cmolc/kg) and low SOM (1.44%-1.86%), accompanied by low total N (0.10%-0.16%) and relatively low to moderate available P (9.5-16.8 mg/kg) and K (65-85 mg/kg) (Win et al., 2024). By contrast, vegetable farms in Nepal showed neutral pH (6.61) and the highest available P (41.1 mg/kg) and K (130.2 mg/kg) among land uses, while traditional cereal-based uplands and lowlands had lower OM, N, and K, highlighting how intensive vegetable production can start from P- and K-enriched soils relative to adjacent cereal systems.

2.2 Initial nitrogen, phosphorus, and potassium status

Baseline NPK status before planting radish is shaped by both land use history and regional fertilization patterns. In greenhouse vegetable soils of Ningxia, 100% of samples at 0-30 cm had low total N (<40 mg/kg) and 84.5% had low available N (<200 mg/kg), whereas available P and K were predominantly high to very high, reflecting long-term P and K accumulation and N depletion under intensive vegetable cultivation (Wang et al., 2025). A similar skewed profile was observed in Nigerian vegetable farms, where topsoil showed moderate to high N (0.14-0.44%) and high P (22-55 mg/kg) but low K (0.05-0.21 mol/kg), indicating that new radish crops in such systems are more likely to face K limitation than N or P scarcity (Yakasai and Rabiu, 2024).

Across broader smallholder landscapes, initial NPK status can be highly variable, requiring site-specific diagnosis before radish establishment. In Limpopo smallholder farms, more than 80% of soils had suitable pH, but P levels were very low (<8 mg/kg) in most samples, with ~95% of fields requiring P fertilization; K, in contrast, was generally adequate (>250 mg/kg) (Mokgolo and Mzezewa, 2023). Farm-gate nutrient budget analysis on organic farms in Germany showed that strong reliance on biological N fixation was associated with negative P and K balances (mean -8 kg P ha^-1 and -18 kg K ha^-1), suggesting that soils entering radish cultivation in legume-heavy organic rotations may already be experiencing hidden P and K mining despite sufficient N supply (Reimer et al., 2020).

2.3 Soil organic matter and microbial baseline conditions

Baseline organic matter and microbial conditions set the context for how radish roots and fertilization will alter soil processes. In a long-term radish monoculture in Poland, soil pH shifted while organic carbon remained stable, and 16S rRNA sequencing showed a community dominated by Proteobacteria, Acidobacteria, and Actinobacteria; enzyme assays revealed marked seasonal variation in dehydrogenase, peroxidase, and C-cycle enzymes, indicating that even under continuous radish, the microbial community tends toward a dynamic equilibrium after disturbances (Nowak et al., 2024). A pot experiment with a single compost application before six successive radish cycles in a tropical Oxisol demonstrated that high-N compost, compared with urea or control, produced sustained increases in plant biomass and long-lasting shifts in bacterial, archaeal, and fungal communities, with new taxa persisting and altered network structure detectable over 227 days (Heisey et al., 2022).

Comparative land-use studies further show how initial SOM and microbial-related properties vary before radish is introduced. In Ethiopia’s Fogera plain, grazing land had the highest organic carbon (4.82%) and total N (0.39%), with elevated EC and available K and P, whereas cultivated cropland had the lowest OC (2.3%), TN (0.15%), and EC, reflecting SOM depletion under continuous cropping (Tiruneh et al., 2021). Similarly, in southwest Nigeria, continuously cropped land had the lowest organic carbon and less stable aggregates than forest and perennial plantations, while total N remained relatively high but available P was low, suggesting that radish established after prolonged annual cropping may encounter compacted, C-depleted soils with constrained biological activity compared to sites converted from forest or tree crops (Akinde et al., 2020).

3 Nutrient Uptake Mechanisms during Radish Growth

3.1 Root development and nutrient absorption capacity

Radish exhibits substantial variation in root system architecture (RSA), which strongly conditions its capacity to explore soil volumes and intercept nutrient resources. Quantitative analysis of 23 accessions showed large genotypic differences in total root length, surface area, branching, and diameter, with landraces generally developing the most extensive, highly branched systems, and cultivated types showing greater root volume and biomass. Strong positive correlations among root length, surface area, projected area, and branching indicate a coordinated architectural strategy that can enhance contact with nutrient-rich microsites and support efficient uptake in contrasting environments (Ochar et al., 2026).

Secondary growth processes further determine how absorbed nutrients are stored and redistributed within developing storage roots. Comparative work on inbred lines with contrasting radial growth demonstrated that higher cambial cell proliferation and stronger cytokinin responsiveness are tightly associated with greater radial expansion and final root biomass in radish. This cytokinin-dependent secondary growth links hormonal regulation to the sink strength of the storage root, implying that genetic differences in cambial activity not only shape root morphology but may also influence nutrient absorption capacity via feedbacks between shoot demand, root growth, and phloem unloading.

3.2 Nitrogen uptake and assimilation pathways

Nitrogen is a central driver of radish growth, and its uptake and internal use efficiency are strongly shaped by external supply. A pot experiment manipulating three N rates showed that increasing N from 0 to 0.300 g N·kg⁻¹ soil enhanced plant height, root length, biomass, and nutritional quality traits, while simultaneously increasing total N concentrations in roots and leaves, reflecting greater N assimilation into structural and metabolic pools. Higher N inputs also elevated nitrate reductase activity in radish tissues, indicating upregulated enzymatic capacity for reducing absorbed nitrate to ammonium, a key step in assimilation (Yousaf et al., 2021).

At the molecular level, nitrate transporter (NRT) genes provide the entry point for inorganic N into roots and its subsequent distribution. A genome-wide survey identified 39 RsNRT genes in radish, distributed across most chromosomes and containing promoter cis-elements linked to phytohormone and abiotic stress responses. Expression profiling revealed that several RsNRT1 and RsNRT2 members, including RsNRT1.1a, RsNRT1.2a, RsNRT1.5a, RsNRT2.1b, RsNRT2.2a, and RsNRT2.3b, are strongly up-regulated under nitrate deficiency, suggesting an adaptive enhancement of root nitrate uptake and translocation capacity when external N is limited (Ding et al., 2023).

3.3 Phosphorus and potassium utilization in root expansion

Phosphorus availability exerts a dual influence on radish, modulating both root system development and internal P allocation among organs. In hydroponic culture with three P levels, low-P conditions promoted higher values for most fine-root morphological traits (e.g., length, branching), consistent with an exploratory response to scarcity, whereas high-P treatment maximized storage root dimensions and biomass. Phosphorus partitioning shifted with supply: low P reduced P content in shoots and tubers, while high P increased P accumulation in roots and maintained tuber P, highlighting a flexible allocation strategy that prioritizes storage organs under adequate P supply (Şavkan et al., 2026).

Mechanistically, radish roots deploy exudation strategies to mobilize sparingly soluble P forms in the rhizosphere. Under P deficiency, radish increased exudation of tartaric, malic, and succinic acids by 15- to 60-fold compared with P-sufficient plants, greatly enhancing dissolution of otherwise poorly available phosphates. In sand culture, this exudation enabled radish to use Al-bound P far more efficiently than Ca-bound P, in contrast to rape, aligning with radish’s natural adaptation to acid soils where Al-P dominates. These findings indicate that organic-acid-mediated solubilization is a key mechanism supporting P uptake and root expansion under low-P conditions.

Potassium plays a complementary role in driving root growth and nutrient accumulation in radish. Field experiments with graded K₂O topdressing showed that increasing K up to 90 kg ha^-1 significantly enhanced root fresh mass, total biomass, and yield, and shifted the macronutrient accumulation pattern in roots to K > P > N, confirming K as the most extracted macronutrient by the storage root. Elevated K supply also increased Mg accumulation in roots and certain micronutrients in shoots, consistent with K’s broader role in supporting cell expansion, osmotic regulation, and assimilate transport required for vigorous root thickening.

4 Temporal Dynamics of Soil Nitrogen during Cultivation

4.1 Transformation of nitrate and ammonium nitrogen

During radish cultivation, the balance between nitrate (NO₃^-) and ammonium (NH₄⁺) in the root zone strongly conditions growth and quality responses. A greenhouse study relating yield parameters to inorganic N forms showed that radish roots were more sensitive to soil NO₃^- than NH₄⁺, with early-season NO₃^- levels primarily driving root yield, while NO₃^- in the second half of the season mainly affected root nitrate concentration and vitamin C content (Zhang et al., 2020). As NO₃^- in the substrate increased, root yield and nitrate content rose, but vitamin C declined, suggesting that temporal NO₃^- accumulation during the crop cycle can improve quantity at the expense of nutritional quality (Zhang et al., 2020).

In intensive vegetable soils, gross N transformation measurements using ¹⁵N tracing revealed that both autotrophic and heterotrophic nitrification rates increase several-fold relative to rice-wheat rotations, leading to rapid conversion of mineralized NH₄⁺ to NO₃^- and net NO₃^- production rates 2.3-5.8 times higher than in non-vegetable soils. Even though NO₃^- immobilization also increased, nitrification outpaced immobilization, causing NO₃^- to accumulate progressively in vegetable fields receiving large ammonium fertilizer inputs; after long-term cultivation and acidification, NH₄⁺ could also accumulate alongside NO₃^-, reflecting inhibition of nitrification under low pH (Figure 1).

4.2 Effects of fertilization on nitrogen cycling

Fertilizer regime strongly shapes how soil N is transformed and retained over the radish cycle. In a pot trial, increasing urea N from 0 to 0.300 g N·kg^-1 soil enhanced radish growth and nutrient content, with urea split between basal and topdressing applications that maintained mineral N supply throughout the season. However, the study primarily reported plant traits and total N uptake, implying that higher N inputs supported sustained mineralization-nitrification processes but also raised the potential for surplus inorganic N remaining in the soil at harvest (Yousaf et al., 2021).

Combining reduced chemical fertilizer with a fixed organic amendment changed both N availability and the biological processes governing N cycling. In a high-mountain radish system, a 20% reduction in chemical fertilizer plus organic fertilizer (T2) increased soil total N by 7.69% relative to the conventional regime, without significantly altering hydrolysable N, and enhanced urease activity by 11.13%, indicating stimulation of urea hydrolysis and mineral N release. Elevated sucrase and alkaline phosphatase activities under T2 further pointed to an active microbial community capable of coupling C and N turnover, helping to maintain N supply while reducing reliance on mineral fertilizer (Jin et al., 2024).

4.3 Nitrogen losses through leaching and volatilization

Nitrate leaching is a major loss pathway in radish and other vegetable systems when fertilization exceeds crop demand. In a four-season radish field experiment, increasing N rates from 0 to 300 g N·kg^-1 caused seasonal nitrate leaching loss (SNLL) and residual soil nitrate to rise exponentially, whereas yield gains plateaued beyond 180 g N·kg^-1; an optimum range of 180-196 g N·kg^-1 maintained high yields while cutting SNLL by about half compared with local farmer practice (Eom et al., 2025). Process-based simulations with DNDC in a similar radish system confirmed that optimized fertilization timing and rate, along with adjusted irrigation, could reduce N use by 40-50% and nitrate leaching by up to 95% over 20-year climate variability, demonstrating that management changes can substantially reshape leaching dynamics across seasons (Lu et al., 2015).

Ammonia (NH₃) volatilization represents another important N loss process in radish cultivation. Field measurements in Korean radish showed that halving the conventional urea rate (117 vs. 234 kg urea ha^-1) did not reduce yield but significantly lowered NH₃ emissions and residual soil N, implying that surplus mineral N at higher rates mainly escaped via volatilization rather than contributing to productivity (Eom et al., 2025). At the system level, a meta-analysis of greenhouse vegetable production reported average N leaching of 297 kg·N·ha^-1·yr^-1 and NO (as a proxy for gaseous N loss) of 12 g·N·kg^-1·yr^-1, with fertilization rate and irrigation explaining much of the variation, underscoring that excessive N inputs and high water use together drive large hydrological and gaseous N losses from intensive vegetable soils (Kováčik et al., 2021).

5 Changes in Soil Phosphorus and Potassium Availability

5.1 Phosphorus fixation and release mechanisms

In intensively cropped vegetable soils, a large fraction of applied phosphate rapidly becomes fixed to soil solids, forming part of a “legacy P” pool that can, in principle, sustain crop production if mobilized effectively. Phosphorus activators such as phosphate-solubilizing microorganisms, organic acids, phosphatases, humic substances, crop residues, and biochar can accelerate transformations that convert this fixed P into plant-available forms, though their performance varies with soil type, pH, and mineralogy. In acid soils, where amorphous and crystalline Al- and Fe-oxides dominate sorption, co-application of negatively charged organic amendments (e.g., charcoal) with alkaline materials (e.g., wood ash) can reduce P sorption sites, shift P among inorganic and organic pools, and decrease fixation to Al, Fe, or Ca phases, thereby increasing P in solution for root uptake (Johan et al., 2021).

Phosphorus sorption-desorption behavior also evolves with the duration of vegetable cultivation. In yellow brown soils under 3-30 years of continuous vegetables, P adsorption data fitted by the Langmuir equation showed that maximum sorption capacity and buffer capacity decline significantly with cultivation time, while the degree of P saturation and desorption rate rise, indicating gradual loading of sorption sites and greater ease of P release. Correlation analysis pointed to amorphous Fe-Al contents as key controls on both adsorption and desorption, underscoring that changes in these reactive phases under long-term fertilization and cropping directly modify the balance between P fixation and release in vegetable systems (Figure 2).

5.2 Potassium exchange and soil retention capacity

Potassium availability to radish depends on the balance between exchangeable K, non-exchangeable K in clay interlayers, and structural K in primary minerals, as well as on how strongly soils retain K against leaching. In coarse-textured Minnesota soils, K sorption was generally low but increased with clay content and cation exchange capacity; the presence of Ca in solution promoted K desorption from exchange sites, revealing that divalent cations can displace K and enhance its mobility in sandy profiles. Freeze-thaw cycles produced mixed effects on K leaching, but simulated irrigation water containing Ca and Mg consistently increased K loss compared with deionized water, emphasizing that both mineralogy and irrigation chemistry determine how much applied K remains available during the crop cycle (Nigon and Kaiser, 2025).

Amendment form and composition can also shape K dynamics in radish soils. Potassium-enriched sewage-sludge biochar-based fertilizers (BBFs), applied at full or half recommended K rates, supplied K as effectively as KCl while simultaneously providing additional nutrients and modifying soil chemical attributes (Fachini et al., 2023). Granular BBFs increased K concentration in radish sap by about 30% relative to pellet BBFs and KCl, whereas pellet BBFs markedly increased tuber dry mass-on average 150% higher than KCl and granular BBFs-indicating that slow-release K sources embedded in carbonaceous matrices can improve K use efficiency and crop performance while potentially altering short-term exchange-retention patterns in the soil-plant system (Fachini et al., 2023).

5.3 Influence of root activity on nutrient mobilization

Root activity is a major driver of P mobilization from fixed pools during radish cultivation. Under low P, many species increase exudation of carboxylate anions (e.g., citrate, malate), which solubilize sparingly available P through ligand exchange and mineral dissolution; however, the magnitude of this response is highly species-specific and strongly influenced by rhizosphere conditions. In radish, rhizobox experiments with mixtures of sand and P-sorbing minerals showed that roots depleted Al-bound P much more strongly than Fe-bound P, and total P uptake from Al-P was 42% higher than from Fe-P, with radish absorbing 34%-90% more P overall than maize; this superior access was linked to greater total organic-acid and carbon exudation into the rhizosphere (Yusuf et al., 2025).

Radish root activity also modifies the local chemical environment and the distribution of co-occurring elements that regulate P sorption. In greenhouse studies, radish grown with different P sources and lime levels reduced rhizosphere concentrations of active Fe, Al, Mn, and Si relative to bulk soil, particularly under lime plus rock phosphate, while simultaneously accumulating “available” Bray-P1 P in the rhizosphere, indicating localized desorption and/or dissolution of sparingly soluble phosphates. More generally, root exudates from fast-growing stages of plants have been shown to restructure bacterial communities, increase functional genes linked to mineralization, and enhance available nitrate, ammonium, P, and K, suggesting that shifts in exudation over the growth cycle feed back on soil microbes to synchronize nutrient mobilization with rising plant demand (Zhao et al., 2020).

6 Effects of Fertilization Practices on Soil Nutrient Dynamics

6.1 Chemical fertilizer impacts on soil nutrient balance

The application of chemical fertilizers remains a primary strategy for enhancing radish growth and yield, but its effects on soil nutrient balance are complex and context-dependent. Studies have shown that increasing nitrogen (N) and magnesium (Mg) fertilizer rates up to optimal levels can significantly improve radish growth, yield, and quality indicators such as plant height, root length, and nutrient content; however, excessive application leads to diminishing returns and may negatively affect certain quality traits like crude fiber content (Yousaf et al., 2021). Similarly, field experiments with varying NPK (nitrogen, phosphorus, potassium) fertilization rates demonstrated that the highest yields and nutrient use efficiencies were achieved at moderate application rates (e.g., 113 kg N ha^-1), while further increases in fertilizer input resulted in reduced efficiency and did not proportionally enhance yield (Choi et al., 2022).

Overuse or imbalanced application of chemical fertilizers can disrupt soil nutrient dynamics by causing nutrient accumulation or depletion. For instance, continuous high-dose N fertilization has been linked to increased nitrate leaching losses and residual soil nitrate, which not only reduces nitrogen use efficiency but also poses environmental risks such as groundwater contamination (Zhang et al., 2020). In soils already rich in phosphorus (P) and potassium (K), additional P or K fertilization did not improve radish productivity or growth parameters, indicating that excessive fertilization may lead to unnecessary nutrient buildup without agronomic benefit. These findings underscore the importance of site-specific fertilizer management to maintain soil health while optimizing crop performance.

6.2 Organic amendments and soil fertility improvement

Organic amendments such as farmyard manure (FYM), poultry manure, vermicompost, biochar, spent coffee grounds, and compost have demonstrated significant potential for improving soil fertility and supporting sustainable radish production. Application of organic manures has been shown to increase soil organic matter content, enhance the availability of macro- and micronutrients (N, P, K, Mg, Zn), and improve physical properties such as bulk density and water-holding capacity (Ceylan et al., 2025). For example, integrating biochar with poultry manure led to substantial increases in soil pH, organic matter, total N%, available P and K levels-resulting in higher marketable yields compared with control or mineral fertilizer treatments (Dahal et al., 2021).

The use of organic amendments also positively influences plant nutrition and crop quality. Poultry manure was found to be particularly effective in boosting both total root yield and biological yield of radish compared to other organic sources (Gautam et al., 2025). Additionally, spent coffee grounds applied at appropriate rates significantly increased the mineral content of both soil and radish tissues without adversely affecting tuber yield or dry matter content (Ceylan et al., 2025). These improvements are attributed not only to direct nutrient supply but also to enhanced microbial activity and enzyme functions that facilitate nutrient cycling within the rhizosphere.

6.3 Integrated nutrient management strategies

Integrated Nutrient Management (INM)-the combined use of chemical fertilizers with organic amendments or biofertilizers-has emerged as a highly effective approach for sustaining soil fertility while maximizing radish productivity. Research indicates that INM strategies such as applying 90% recommended dose of fertilizers plus 10% spent mushroom compost (SMC), FYM, Azotobacter, and phosphate-solubilizing bacteria can increase the availability of NPK by over 13% compared with conventional practices (Shilpa et al., 2022). Such integrated modules have been associated with improved root size, weight, yield attributes, as well as enhanced soil health indicators including enzyme activities and beneficial microbial populations (Jin et al., 2024).

Field trials further demonstrate that substituting a portion of chemical fertilizer with organic inputs does not compromise yield; rather it often results in superior quality attributes-such as higher vitamin C content-and improved economic returns due to reduced input costs (Basnet et al., 2021; Jin et al., 2024). The integration of bio-organic fertilizers has also been shown to alter the soil microbial community structure favorably while reducing nitrate accumulation in edible tissues-a key consideration for food safety (Qi et al., 2025). Overall, INM approaches offer a balanced solution for maintaining long-term soil fertility by leveraging the complementary benefits of both synthetic nutrients and organic matter inputs.

7 Environmental Drivers of Soil Nutrient Transformation

7.1 Soil moisture effects on nutrient mobility

Soil moisture regimes during radish cultivation strongly influence nutrient mobility and uptake. In cherry radish, stable soil water (via negative-pressure irrigation) increased N, P, and K uptake by 23.6%-60.9%, 32.8%-80.1%, and 6.5%-55.7%, respectively, compared with fluctuating water regimes at similar average water contents, mainly by supporting greater biomass production rather than higher tissue nutrient concentrations (Li et al., 2024). This indicates that maintaining relatively constant water availability can enhance nutrient mass flow and root exploration, thereby intensifying nutrient extraction from the soil profile under root vegetable systems (Li et al., 2024).

Field work on drip-irrigated radish further shows that soil water potential (SWP) thresholds modulate water use efficiency (WUE) and indirectly nutrient delivery. When SWP at 20 cm was controlled between -15 and -55 kPa, yields were similar, but drier targets expanded the dry domain in the root zone and altered root distribution, with an optimum around -35 kPa balancing WUE, cracking rate, and market quality. These moisture patterns determine the thickness and continuity of the water film around soil particles, affecting diffusion of dissolved nutrients and the spatial overlap between active roots and nutrient-rich microsites during the crop cycle.

7.2 Temperature influence on nutrient transformation

Temperature is a primary control on soil nitrogen mineralization, thereby shaping plant-available N dynamics during radish growth. A global synthesis of 379 studies found an average net N mineralization rate of 2.41 mg·N·kg^-1 soil day^-1 and a mean Q₁₀ (temperature sensitivity) of 2.21, with higher Q₁₀ values in colder regions, implying that warming disproportionately accelerates N mineralization in cooler climates. Net mineralization was mainly governed by soil organic carbon, C:N ratio, and clay content, suggesting that temperature effects on N supply in radish systems will be mediated by substrate quantity and quality.

Laboratory incubations of agricultural soils across 5°C-25 °C showed Q₁₀ values for N mineralization averaging 2.87 and largely independent of soil organic matter, texture, EC, or pH, indicating a broadly consistent thermal response across contrasting cropping regions. Coupling this temperature response with field temperature data highlighted strong seasonal shifts in mineralization rates, underscoring that planting date and crop duration in radish must be aligned with local temperature regimes to synchronize N release from soil organic matter with peak crop demand.

7.3 Microbial activity and nutrient cycling

Microbial communities mediate most soil nutrient transformations affecting radish nutrition, and their activity responds sensitively to management and environment. Across 13 organic fields, potential activities of nine C-, N-, P-, and S-cycling enzymes varied strongly with soil C and inorganic N availability, while microbial community composition (FAME profiles) was relatively stable (Eom et al., 2025), indicating high functional plasticity of microbes under different organic nutrient management regimes. C-cycling enzyme activities increased with inorganic N, and N-cycling enzymes increased with soil C, showing tight coupling between resource supply and microbial function that will regulate nutrient turnover in radish systems.

At the global scale, analysis of 1,565 observations showed that net N mineralization increased with soil microbial biomass, total N, and mean annual precipitation, but declined with rising pH, with microbial biomass emerging as the dominant driver of mineralization across ecosystems. Structural equation modeling revealed that climate and soil properties influence N mineralization mainly through their effects on microbes, emphasizing that any shifts in microbial biomass or activity induced by radish cultivation, irrigation, or residue management will directly reshape N availability and broader nutrient cycling (Chen et al., 2025).

8 Case Study on Soil Nutrient Variation in Radish Field Experiments

8.1 Experimental site and soil conditions

Field and pot experiments on radish have been conducted across a wide range of climatic zones and soil types, which strongly influences baseline nutrient status and subsequent dynamics. For example, a pot study in Punjab, Pakistan used a loamy soil (0-20 cm) with pH 7.24, organic C 0.56%, total N 0.023%, Olsen-P 8 mg/kg and exchangeable K 172 mg/kg, representing a low-N, low-P but K-rich substrate typical of arid regions with high evaporative demand (Yousaf et al., 2021). In contrast, multi-site field datasets compiled for QUEFTS modeling in China covered 28 provinces with diverse soils and climates, from coastal alluvials to upland loams, and were explicitly characterized for texture, indigenous nutrient supply, and management to capture the breadth of radish-growing environments.

Several field trials explicitly detail initial soil fertility when evaluating fertilization effects. In North-western Himalayas, radish was grown on sandy loam soil under varying irrigation and N levels, and the study emphasized how this texture and climate combination makes nutrient retention and loss particularly sensitive to water management (Sharma et al., 2023). Similarly, biochar-poultry manure field experiments in Nigeria were established on initially low-fertility soil with low organic matter and nutrient levels, chosen to highlight how amendments could alter soil physical and chemical properties, including pH, organic matter, and available N, P, K, Ca, and Mg for radish production (Figure 3).

8.2 Monitoring nutrient dynamics during growth stages

Temporal patterns of soil inorganic N during radish growth have been quantified by relating yield and quality to measured ammonium and nitrate at different growth stages. Greenhouse experiments showed that radish yield depended mainly on nitrate (N-NO₃^-) levels early in the season, whereas nitrate present in the second half of the season primarily affected root nitrate concentration and vitamin C, with increasing soil nitrate leading to higher root nitrate but reduced vitamin C content. These measurements were based on repeated sampling of the growing medium, demonstrating that soil N availability declines during growth while its qualitative effects on root composition intensify later in the cycle (Kováčik et al., 2021).

Field monitoring of multi-nutrient dynamics reveals how management alters N, P, and K availability over time. In a mid-hill Himalayan radish system, combinations of irrigation scheduling (IW/CPE 0.8-1.2) and N levels (0-100% recommended dose) significantly changed post-harvest soil available N, P, K, Ca, Mg, and sulfate-S, with higher irrigation and N generally increasing nutrient availability and uptake but lowering N use efficiency (Sharma et al., 2023). Integrated nutrient management trials in India reported that treatments combining 90% recommended fertilizers with spent mushroom compost, farmyard manure, and biofertilizers increased soil available N, P, and K by 15.17%, 18.66%, and 13.0% over the control, indicating that repeated measurements across the season and at harvest can capture cumulative effects of fertilization on the soil nutrient pool (Shilpa et al., 2022).

8.3 Implications for fertilizer optimization strategies

Case-study evidence from Chinese radish regions shows that fertilizer optimization must account for both plant demand and soil indigenous supply to maintain yields while stabilizing soil nutrients. Using on-farm datasets from 2000-2017, the QUEFTS model estimated balanced N, P, and K requirements of 2.15, 0.45, and 2.58 kg per 1000 kg fleshy root, and indicated that 62%-75% of plant N, P, and K is exported in roots, implying substantial soil nutrient mining under insufficient fertilization. Complementary field validation of the Nutrient Expert (NE) decision support system across 46 sites in North China showed that NE recommendations could reduce N, P₂O₅, and K₂O inputs by 98, 110, and 47 kg/ha relative to farmers’ practice while increasing yield by about 4%, improving agronomic and recovery efficiencies, and cutting N and P surpluses and apparent N loss (Zhang et al., 2022).

Other field experiments refine these strategies by testing specific fertilizer rates and sources. Integrated nutrient management in radish cv. Japanese White demonstrated that 90% recommended mineral fertilizer combined with spent mushroom compost, farmyard manure, Azotobacter, and phosphate-solubilizing bacteria raised soil available N, P, and K and increased root yield by 11.44% over standard practice, indicating that partial substitution of mineral fertilizer can enhance both soil nutrient status and productivity (Shilpa et al., 2022; Chen et al., 2025)). Long-term optimization studies using the DNDC model in a typical radish field in northern China further suggested that adjusting planting dates, irrigation, and fertilizer rate and timing could cut N use by 40%-50% and nitrate leaching by up to 95% while maintaining or improving yield, highlighting how site-specific strategies derived from field data can reconcile crop performance with soil and environmental protection (Zhang et al., 2021).

9 Sustainable Soil Fertility Management in Radish Production Systems

Optimizing fertilizer rates can maintain high radish yields while reducing nutrient surpluses and losses. In North China, use of the Nutrient Expert (NE) decision support system cut N, P₂O₅ and K₂O inputs by 98, 110 and 47 kg/ha relative to farmers’ practice yet increased yield by about 4% and greatly improved agronomic and recovery efficiencies of N, P and K, while lowering N and P surpluses and apparent N loss (Zhang et al., 2022). A broader NE development study using 247 datasets showed large yield responses to N, P and K and derived response-efficiency relationships that underpin site-specific recommendations, confirming that fertilizer demand should be matched to indigenous soil supply and expected yield response rather than fixed blanket doses.

Rate and splitting of N applications also affect plant performance and environmental risk. A pot experiment with graded N and Mg showed radish growth, yield and nutrient content increased as N rose to 0.300 g N·kg^-1 soil, but quality traits such as crude fiber were sensitive to higher Mg levels, indicating an optimum N-Mg window beyond which returns decline (Yousaf et al., 2021). Field work in Korean radish revealed that halving the recommended urea rate (117 vs. 234 kg·urea·ha^-1) did not reduce yield, while markedly decreasing ammonia volatilization, suggesting that current recommendations may exceed crop demand and that lower N rates with appropriate timing can sustain productivity and improve nitrogen use efficiency.

Organic amendments can conserve soil quality while sustaining or increasing radish yield. In a high-mountain system, reducing chemical fertilizer by 20% while maintaining a fixed organic input increased soil total N and P by 7.69% and 14.29%, and enhanced key enzymes (urease, sucrase, alkaline phosphatase, catalase), indicating improved nutrient cycling and biological activity alongside a 12.9% yield gain. Similarly, integrating rice husk biochar (3 t/ha) with farmyard manure and vermicompost in organic soil improved macroaggregate stability, soil moisture, infiltration, and water use efficiency, and raised radish yield by 16%-31% compared with non-amended control, demonstrating the dual benefits of C-rich amendments for structure and productivity.

Use of animal manures and composts also supports sustainable nutrient supply and economic returns. A field study comparing combinations of farmyard manure, vermicompost and poultry manure found that a 50:50 mix of vermicompost and poultry manure produced the highest radish yield (280 q/ha) and the best benefit-cost ratio, indicating that well-balanced organic sources can replace or substantially reduce mineral fertilizers while maintaining profitability. Trials with different organic nutrient sources showed poultry manure alone gave the greatest total root and biological yields, further highlighting that manures can both enhance organic matter and supply readily available nutrients when properly managed.

Decision support and precision tools can align fertilizer inputs with spatial and temporal crop needs in radish systems. The NE system for radish, built from regional yield response and agronomic efficiency data, uses indigenous nutrient supply and target yields to generate field-specific N, P and K recommendations; validation trials showed NE out-performed farmers’ practice and soil-test approaches by increasing yield and profitability while reducing nutrient surpluses. Subsequent multi-season validation confirmed that NE reduced N and P₂O₅ applications by 48 and 44 kg/ha versus soil testing yet still raised yields and nutrient use efficiency, and cut apparent N loss by about 111 kg/ha, illustrating how algorithm-based prescriptions can support cleaner production at scale.

More generally, precision agriculture frameworks couple sensing and variable-rate application to manage within-field variability in soil fertility and crop status. Reviews of precision nutrient management emphasize that proximal and remote sensors, GPS-guided machinery, and digital prescription maps enable site-specific N fertilization, improving nutrient use efficiency and reducing leaching or localized accumulation that can create environmental problems. A newer UAV- and GIS-based soil nutrient monitoring and fertilization system achieved 18%-27% fertilizer savings and 4%-11% yield increases across several zones by integrating hyperspectral imagery, ground sensors and dynamic models to generate real-time variable-rate fertilizer recommendations, offering a scalable pathway to fine-tuned nutrient management in vegetable production landscapes.

Acknowledgments

I would like to thank the anonymous reviewers for their detailed review of the draft. Their specific feedback helped us correct the logical loopholes in our arguments.

Conflict of Interest Disclosure

The author affirms that this research was conducted without any commercial or financial relationships that could be construed as a potential conflict of interest.

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