Monitoring soil is essential for understanding and maintaining soil health, ensuring agricultural productivity, and addressing environmental challenges such as land degradation and climate change. Conventional methods for evaluating soil properties, although precise, are often labor-intensive, time-consuming, and unsuitable for large-scale or near real-time applications. This has created a strong demand for innovative, cost-effective, and scalable techniques to characterize soils. Hyperspectral sensing—using both point-based and imaging sensors—has emerged as a powerful solution, capable of capturing detailed spectral signatures that reveal a wide array of soil attributes, including soil organic carbon (SOC), texture, carbonates, and moisture content. A key element in advancing these techniques is the creation of spectral libraries—comprehensive datasets of soil spectra—that enable robust modelling and prediction of soil properties in various environments. This study aims to demonstrate preliminary modelling results for soil property estimation using a local soil spectral library from Kopaida plain, central Greece, for soil property assessment, with a focus on estimating SOC and calcium carbonate content. Standard laboratory procedures were applied to determine soil chemical and physical properties, with SOC quantified via wet oxidation, and calcium carbonate percentage was estimated using Bernard test. Several statistical modelling approaches—Partial Least Squares Regression (PLSR), Random Forest (RF) and Ridge regression—were tested. Modelling accuracy was assessed using Root Mean Square Error (RMSE), the coefficient of determination (R²), and the Ratio of Performance to Interquartile Range (RPIQ). The findings highlight the considerable potential of the developed spectral library for accurately estimating soil properties and contribute to sustainable land management. By capitalizing on the strengths of hyperspectral sensing, this method offers a rapid, scalable, and precise means of monitoring soil conditions across diverse landscapes. Such advancements are crucial for promoting soil sustainability, enabling targeted conservation actions, and supporting agricultural productivity under the pressures of climate change.

A global meta-analysis was conducted to assess how various abiotic factors influence grain yield (GY) and grain protein content (GPC) of bread wheat. For this purpose, forty peer-reviewed papers published between 1986 and 2024 were analyzed. The results showed that the application of supplemental irrigation had significant effects on GY and GPC depending on the climate. In a semi-arid climate, supplemental irrigation had a positive effect on the yield, increasing it by 1,154.08 kg ha^-1, and a negative effect on GPC, decreasing by 2.09%. However, in a sub-humid climate, a yield decrease of 499.25 kg ha^-1 was observed. In addition, GY and GPC responses to supplemental irrigation were significant according to soil textures (p<0.0001). When irrigation was applied, the highest GY increase was observed in coarse- and fine-textured soils (1,507.41 kg ha^-1 and 1,826.18 kg ha^-1, respectively). However, the medium-textured soils indicated negative responses (MD=-1,811.63 kg ha^-1). Indeed, the beneficial effect of supplemental irrigation on GPC was demonstrated in fine-textured soils (MD=0.91%). However, a negative response of irrigation was observed in coarse- (MD=-1.67%) and medium-textured (MD=-1.60%) soils. When no tillage was implemented, GY response was positive in both sub-humid and humid climates, leading to an increase by 1,660.41 kg ha^-1 and 1,650.02 kg ha^-1, respectively. In contrast, no tillage led to a decreased GY (by 499.25 kg ha^-1) in the semi-arid climate. Although no tillage had no significant impact on GPC alone, GY and GPC showed positive responses, leading to an increase by 201.36 kg ha ^-1 and 0.13% in coarse-textured soils and 1,390.57 kg ha^-1 and 1.11% in medium ones, respectively. However, a negative response to no tillage was observed in fine-textured soils (MD=-0.45%).

Introduction

Food security is increasingly challenged by climate change, soil degradation, and water scarcity. Although chemical fertilizers have boosted agricultural productivity, their excessive use can degrade soil fertility, contaminate water resources, and leave residues in crops, thereby raising concerns for food quality and safety. In this context, sustainable organic inputs provide an alternative strategy that not only improves soil health but also enhances the nutritional and functional properties of agricultural products. Tomatoes, being among the most consumed vegetables and a major source of antioxidants and vitamins, offer an ideal model to study the link between soil management and food quality.

Materials and Methods:
A field experiment was carried out under semi-arid conditions. Tomato plants were grown under two controlled water-stress regimes and amended with locally produced organic inputs derived from horse manure vermicompost, applied at two concentration levels. Soil physicochemical characteristics, plant physiological responses, and fruit quality traits were assessed, with a focus on bioactive compounds and indicators relevant to nutritional value and food safety.

Results:
Organic amendments improved soil fertility and water retention capacity, along with enhanced microbial activity. At the physiological level, plants showed better leaf relative water content (RWC) and stronger responses to drought stress. Fruit analysis revealed significant increases in lycopene, ascorbic acid , protein content , enhanced antioxidant capacity (DPPH), and extended shelf life. Notably, higher organic inputs achieved the most consistent improvements across these parameters.

Conclusions:
This study highlights the close connection between soil management and food quality. By enhancing soil fertility and improving the nutritional and postharvest traits of tomatoes, organic approaches represent a promising pathway to produce safe, nutritious food while contributing to sustainable food security under climate challenges.

Humic substances (HS), derived from the degradation of organic matter in terrestrial and aquatic systems, play critical roles in nutrient cycling, metal complexation, and soil fertility. Their ability to bind trace elements, including molybdenum, is of particular agricultural importance, as Mo is an essential micronutrient that regulates nitrogen fixation and assimilation. Despite Mo’s pivotal role, its solubility and bioavailability in soils remain limited, often resulting in plant deficiencies. Understanding Mo–HS interactions is therefore crucial for developing sustainable strategies to improve nutrient availability.

HS samples obtained from Greek peaty lignite (leonardite) were studied for their interaction with Mo(VI). Solutions of HS were titrated with Mo(VI) and analyzed. Mo concentrations in supernatants were determined via atomic emission spectroscopy. Solid residues containing Mo–HS complexes were characterized using UV–Vis spectroscopy and FTIR spectroscopy.

The addition of Mo(VI) to HS solutions decreased pH, consistent with proton-releasing complexation reactions. UV–Vis spectra revealed charge-transfer processes indicative of Mo–HS associations without Mo reduction. FTIR analyses confirmed the involvement of functional groups—primarily carboxylic, with additional contributions from phenolic and alcoholic moieties—in Mo binding. Shifts and intensity changes in COO–, C=O, and O–H vibrations substantiated the formation of stable complexes.

This study demonstrates that HS effectively complexes Mo(VI), thereby enhancing its solubility and potential bioavailability in soils, highlighting the agronomic potential of humic-rich materials, such as leonardite, as natural Mo carriers to improve crop nutrition. These findings contribute to the broader understanding of HS-mediated trace element dynamics and their role in sustainable agriculture.

References

Gustafsson, J.P., Tiberg, C. Chem. Geol. 2015, 417, 279–288.

Chassapis, K.; Roulia, M.; Tsirigoti, D. Int. J. Coal Geol. 2009, 78, 288–295.

Korshin, G.V.; Li, C.-W.; Benjamin, M.M. Water Res. 1997, 31, 1787–1795.

Chassapis, C.; Angelopoulos, C.; Katakis, D. Int. J. Coal Geol. 1989, 11, 303–314.

Chassapis, K.; Roulia, M.; Nika, G. Fuel, 2010, 89, 1480–1484.

Humic substances (HSs), derived from organic matter degradation in terrestrial and aquatic systems, play critical roles in nutrient cycling, metal complexation, and soil fertility. Their ability to bind trace elements, including molybdenum, is of particular agricultural importance since Mo is an essential micronutrient regulating nitrogen fixation and assimilation. Despite Mo’s pivotal role, its solubility and bioavailability in soils remain limited, often leading to deficiencies in plants. Understanding Mo–HS interactions is therefore crucial for developing sustainable strategies to improve nutrient availability.

HS samples obtained from Greek leonardite were studied for their interaction with Mo(VI). Solutions of HS were titrated with Mo(VI) and analyzed. Mo concentrations in supernatants were determined via atomic emission spectroscopy. Solid residues containing Mo–HS complexes were characterized using UV–Vis spectroscopy and FTIR spectroscopy.

The addition of Mo(VI) to HS solutions decreased pH, consistent with proton-releasing complexation reactions. UV–Vis spectra revealed charge-transfer processes indicative of Mo–HS associations without Mo reduction. FTIR analyses confirmed the involvement of functional groups—primarily carboxylic, with additional contributions from phenolic and alcoholic moieties—in Mo binding. Shifts and intensity changes in COO–, C=O, and O–H vibrations substantiated the formation of stable complexes.

This study demonstrates that HSs effectively complex Mo(VI), enhancing its solubility and potential bioavailability in soils, highlighting the agronomic potential of humic-rich materials, such as leonardite, as natural Mo carriers for improving crop nutrition. These findings contribute to the broader understanding of HS-mediated trace element dynamics and their role in sustainable agriculture.

References

Gustafsson, J.P., Tiberg, C. Chem. Geol. 2015, 417, 279–288.

Chassapis, K.; Roulia, M.; Tsirigoti, D. Int. J. Coal Geol. 2009, 78, 288–295.

Korshin, G.V.; Li, C.-W.; Benjamin, M.M. Water Res. 1997, 31, 1787–1795.

Chassapis, C.; Angelopoulos, C.; Katakis, D. Int. J. Coal Geol. 1989, 11, 303–314.

Chassapis, K.; Roulia, M.; Nika, G. Fuel, 2010, 89, 1480–1484.

Different maize hybrids vary in nutrient uptake efficiency. Plant density influences nutrient absorption, which affects yield at different growth stages such as germination, tasselling, and kernel development. Few studies have examined the relationship between soil electrical conductivity (EC) and maize yield under varying plant densities. This research aimed to identify optimal hybrid–density combinations for improved productivity and resource use efficiency. The experiment was conducted in 2024 at the Látókép Experimental Station (Debrecen, Hungary) under strip tillage on non-irrigated chernozem soil. Three maize hybrids (Merida, Fidencio, and P9985) were cultivated at two plant densities (60,000 and 80,000 plants ha^-1) with a fertiliser rate of 80 kg Nitrogen ha^-1 plus basal Phosphorus and Potassium. Soil EC was measured monthly with a portable sensor from planting to cob formation, and grain yield was determined at harvest. Data were aggregated by hybrid–plant density and statistically analysed using SPSS Software (IBM v20), with significance evaluation at p ≤ 0.05. Results revealed no significant correlations among hybrid, EC, plant density, and yield. This shows that neither EC nor plant density reliably predicts yield, suggesting other factors, such as soil moisture and fertility, that may exert stronger influence. Future studies should examine interactions between EC and other factors affecting maize productivity. Moreover, long-term studies across multiple seasons and diverse soil types could clarify EC patterns under varying environmental conditions, tillage systems, and irrigation regimes.

Soil nutrient management in citrus orchards across central India still largely follows traditional, uniform guidelines that overlook the spatial variability of environmental conditions. This often results in unbalanced blanket fertilization, inconsistent yields, and reduced fruit quality, ultimately affecting farmers’ profitability. This study aimed to assess the spatial variability of soil properties in citrus orchards on the Malwa Plateau in central India using geostatistical techniques and to delineate potential management zones through principal component analysis and fuzzy c-means clustering. A total of 104 orchards were selected in the citrus-growing areas of the Rajgarh region, Madhya Pradesh. Surface soil samples (0–20 cm depth) were collected in 2022 to analyze pH, electrical conductivity (EC), organic matter, and levels of primary, secondary, and micronutrients. The data were subjected to descriptive and geostatistical analyses. Management zones were delineated using clustering methods, with the optimal number of zones determined by the Fuzziness Performance Index and Fuzzy Partition Entropy.

Results revealed significant spatial variability in soil properties, with three distinct management zones identified as optimal for citrus orchards. Most soil attributes varied significantly across these zones. Based on these delineated zones, preliminary zone-specific nutrient management guidelines were developed, suggesting differentiated fertilizer rates and organic matter inputs tailored to each zone’s fertility status. The developed recommendations system optimizes nutrient application, uses efficiency, further integrates the Diagnosis and Recommendation Integrated System (DRIS), and develops a nutrient management zone. The validity is better than blanket fertilizer recommendations, which further improve fruit yield and quality and provide practical decision-support tools for farmers and extension services.

This study provides a foundation for implementing site-specific nutrient management. It supports broader adoption of precision agriculture in central India, contributing to more sustainable, resilient citrus production systems.

This study examined the effects of Municipal Refuse Waste (MRW) used as fertilizer on soil physical and chemical properties in three Local Government Areas of Kano State, Nigeria, where MRW mainly contained decomposed organic matter, food residues, ash, and limited inert materials, with variable composition that may influence soil and environmental outcomes. Nine farmlands applying MRW and three control sites without MRW were selected. Each site was stratified, and five surface (0–15 cm, because the cultivated arable crops obtain most nutrients within the rhizosphere zone) soil samples were randomly collected per stratum and composited. However, further work will consider 15–30 cm layers to assess nutrient and metal leaching. Samples were analyzed for texture, fertility, and metal content using standard laboratory methods.

Results revealed loamy-sand textures across all soils, with MRW-treated soils showing lower sand (77.22–78.55%) and higher silt (15.00–17.67%) and clay (4.89–7.78%) fractions than the control (82.77% sand, 13.23% silt, 4.00% clay). Soil pH (6.05–6.32) slightly decreased compared with the control (6.40). Fertility parameters, including organic carbon (up to 0.79%), likely due to organic matter decomposition, total nitrogen (0.10–0.17%), available phosphorus (up to 30.81 mg kg⁻¹), and exchangeable bases such as calcium (2.32–3.33 cmol kg⁻¹) and magnesium (2.03–2.77 cmol kg⁻¹), were significantly enhanced.

Heavy-metal concentrations were determined using mild acid extraction (0.5 M HCl + 0.012 M H₂SO₄) and Atomic Absorption Spectrophotometry, which measures available fractions (bioavailable). Iron ranged from 11.29–12.10 mg kg⁻¹, manganese 18.77–26.25 mg kg⁻¹, zinc 10.05–38.94 mg kg⁻¹, and chromium 0.0387–0.0518 mg kg⁻¹. Lead levels exceeded safety limits in some sites, notably Ungogo. Although MRW improved soil fertility, variation in its composition and elevated metal levels highlight the need for cautious use and deeper assessments to evaluate long-term environmental and food-safety implications.

Sustainable agricultural productivity depends on soil quality and management practices. Integrated crop–livestock systems offer a promising pathway to enhance agri-food system resilience through soil quality improvement. This study evaluates soil quality dynamics under varying integration levels in a Mexican agricultural region characterized by conventional monoculture maize production, addressing critical gaps in sustainable transition strategies. Four farming systems were compared, FS1 (low-integration system: maize monoculture, no grazing) and three medium–high-integrated systems, all of them including grazing: FS2 (grass + legume), FS3 (grass + maize + cover crop), and FS4 (grass + maize + legume). Soil samples were collected at the beginning and end of two crop cycles, with physical and chemical properties analyzed. Key soil quality indicators were identified via Principal Component Analysis (PCA) and aggregated into a Soil Quality Index (SQI) for each farming system. Monoculture maize (FS1) exhibited a significant decline (P=0.001) in SQI (13.8) compared to higher-integrated systems (average SQI=17.7) by the end of the evaluation period. Legume integration (FS2 and FS4) consistently improved SQI, underscoring its role in soil health. PCA identified organic matter, nitrogen, and bulk density as primary drivers of soil quality differentiation. Higher-integrated farming systems significantly mitigate soil degradation compared to monocultures, with legume inclusion offering additional benefits. SQI provides a robust tool for monitoring management practices and guiding sustainable transitions. These findings advocate policy and practitioner prioritization of diversified systems to reconcile productivity with environmental sustainability in farming systems. Acknowledgements: The authors wish to thank the UNAM (Project: CI 2454) for providing financial and institutional support for this study.

The blue–red spectrum, widely used in vertical farming due to its alignment with chlorophyll absorption and its role in regulating secondary metabolism, can be supplemented with wavelengths such as far-red to improve cultivation in fully controlled environments. The aim of this research was to determine the impact of adding FR light to the blue (B), red (R), and blue–red (BR) spectra on the growth, pigment content, and mineral profile of green- and purple-leaf lettuce grown hydroponically in a vertical farm. Plants were cultivated under B, R, and BR spectra with or without FR addition (total PPFD ~150 µmol m⁻² s⁻¹; 16 h light). The addition of FR light, particularly to the red spectrum (R+FR), significantly increased fresh weight, between 36.6% and 141.5% in green lettuce and between 13.1% and 104.9% in purple lettuce compared to other treatments, due to the higher relative growth rate. Moreover, this treatment also caused a reduction in the percentage of dry matter, which ranged from 7.88% to 20.7% in green lettuce and from 8.43% to 24.8% in purple lettuce, compared to other treatments. In green lettuce, chlorophylls (Chl) a and b increased independently under BR and with FR addition. In purple lettuce, Chl a rose with B, while Chl b improved with the B+FR interaction. In green lettuce, carotenoid levels increased significantly with the BR-FR interaction, while in purple lettuce, they augmented significantly with B, and in the absence of FR, independently. Finally, anthocyanin content increased significantly with the B-FR interaction, followed by BR-FR. Although the intensity of these responses varied among cultivars, the results highlight the importance of adapting light spectra to maximize both yield and nutritional value in indoor growing systems. This knowledge lays the foundation for designing precise lighting protocols that respond to different production objectives in vertical farming with different lettuce cultivars.