Circular agriculture reclaims nutrients from waste streams to reduce fertilizer imports, mitigate environmental impacts, and close material loops. This review evaluates the agronomic performance of nitrogen, phosphorus, and potassium products recovered from wastewater, crop residues, and manure compared with conventional fertilizers. A structured literature survey identified 85 pot and field trials published between 2010 and 2024, covering ammonium salts, struvite, ashes, compost, digestate, biochar, hydrochar, and biostimulants. Ammonium sulfate and nitrate consistently matched synthetic yields (95–105%) due to their solubility and immediate N availability, while aqueous ammonia showed variable results depending on application timing and soil pH. Struvite and phosphorus-rich ashes performed best (90–100%) in neutral to slightly acidic soils, whereas organo-mineral phosphate fertilizers (85–95%) were less effective in alkaline soils. Potassium-rich ashes and waste mica were effective (80–95%) in soils with moderate cation exchange, though mica underperformed (60–75%) in coarse soils. Biochars and hydrochars improved soil water retention and nutrient exchange, yielding 90–110% of synthetic performance, while biostimulants increased yields by 8–20%. Recovered products demonstrate agronomic equivalence while offering co-benefits for soil health, waste management, and circular economy goals. Future work should prioritize long-term field validation, techno-economic analysis, and regulatory integration to enable large-scale adoption.

Laboratory experiments were conducted to investigate the effects of NPK fertilizer, soil type (silty clay and sandy loam) with no history of pesticide application, temperature (28 and 40 °C), and maize residue on the half-life of atrazine herbicide. NPK fertilizer was applied at 375 mg N, 187.5 mg P, and 187.5 mg K per 600 g soil, while maize straw was added at a rate of 12 g per 600 g soil. Atrazine was applied at four concentrations: 0.0678, 1.69, 3.39, and 5.08 mg g−1 soil. The residual concentration of atrazine was measured using gas chromatography over a 150-day period. The results showed that atrazine degradation was highest in Algeraif soil at 40 °C (87%), followed by Algeraif soil at 28 °C (68%) and Gerif soil at 28 °C (54.2%). The addition of NPK and maize straw significantly enhanced atrazine degradation, with degradation reaching 97% at a concentration of 0.0678 mg g−1 soil after 150 days. The lowest half-lives, compared to the control, were 125, 39, 25, 19, and 14 days in Gerif soil (28 °C), Algeraif soil (28 °C), Algeraif soil (40 °C), NPK, and maize straw, respectively, at an atrazine concentration of 5.08 mg g−1 soil. In conclusion, the addition of NPK fertilizer and maize straw significantly enhanced atrazine degradation, reducing both its concentration and half-life in soil.

To explore fertilization strategies that achieve both high yield and emission reduction in greenhouse tomato production, a two-season experiment was conducted in autumn 2023 and spring 2024 under equal nitrogen input. Seven treatments were established: conventional fertilization (CK1), biogas slurry alone (CK2), 0.5% biochar + biogas slurry (T1), 2% biochar + biogas slurry (T2), dicyandiamide + biogas slurry (T3), 0.5% biochar + biogas slurry + dicyandiamide (T4), and 2% biochar + biogas slurry + dicyandiamide (T5). The effects of each treatment on tomato root traits, yield, irrigation water use efficiency (IWUE), partial factor productivity of nitrogen (PFPN), and soil N2O emissions were systematically evaluated. An analytic hierarchy process (AHP) was applied for comprehensive assessment. The results showed that fertilization treatments significantly affected tomato root traits (p < 0.05), with T5 exhibiting the best performance in root length, average diameter, total surface area, total volume, and root activity, all significantly higher than CK1. T5 also achieved the highest yield in both seasons, with increases of 8.13% (autumn 2023) and 10.19% (spring 2024) over CK1. Moreover, T5 showed superior IWUE (475.38 kg ha−1 mm−1) and PFPN (405.92 kg kg−1). In terms of environmental performance, T5 significantly reduced soil N2O flux, with the largest reduction reaching 16.16%, particularly during the peak emission stages in the flowering and fruit-setting periods. The AHP-based comprehensive evaluation confirmed that T5 had the highest overall weight with satisfactory matrix consistency. In conclusion, compared with conventional fertilization, the integrated T5 treatment increased tomato yield by up to 10.19% and reduced cumulative N2O emissions by up to 16.16%, highlighting its potential as a feasible fertilization pathway and technical reference for low-carbon and sustainable agriculture.

As interest in biochar as a soil amendment increases, the co-application of biochar and fertilizer warrants investigation. Biochar may improve soil properties, affect crop yields, and mitigate environmental impacts, but more work is needed to determine its effect on nitrogen (N) cycling from commercially available organic fertilizers. A 102 d laboratory incubation was conducted to better understand the effect of three rates of biochar (0%, 5%, and 10%) on net N mineralized from (1) mineral soil (Cecil sandy loam), (2) organic peat-based potting media, and (3) two commercial organic fertilizers (feather meal and meal-based pellet mix) applied to the mineral soil or the potting media. After 102 d, the biochar treatments did not affect net N mineralized from the mineral soil but decreased (from 190 to −286.9 mg N kg−1) the net N mineralized from the potting media, likely due to N immobilization. Biochar applied at 5 or 10% did not affect the amount of organic N mineralized from the organic fertilizers applied to potting media (average 58.9%), but biochar at 5% decreased from 46.5 to 28.1% of organic N mineralized from the organic fertilizers applied to mineral soil.

Grassland biomass yield reflects a complex interaction of management intensity and environmental factors, yet quantifying the relative role of practices such as mowing and fertilization remains challenging. In this study, we introduce a multi-class machine learning framework to predict above-ground biomass on 150 permanent grassland plots across eight years (2009–2016) in Germany’s Biodiversity Exploratories and to evaluate the influence of key management variables. Following rigorous data cleaning, imputation of missing nitrogen values, feature standardization, and encoding of categorical practices, we trained CatBoost classifiers optimized via Bayesian hyperparameter search and mitigated class imbalance with ADASYN oversampling. We assessed model performance under binary, three-class, four-class, and five-class quantile-based categorizations, achieving test accuracies of 0.76, 0.57, 0.42, and 0.38, respectively. Across all schemes, mowing frequency and mineral nitrogen input emerged as the dominant predictors, while secondary variables such as drainage and conditioner use contributed as well. These results demonstrate that broad biomass categories can be forecast reliably from standardized management records, whereas finer distinctions necessitate additional environmental information or automated sensing to capture nonlinear effects and reduce reporting bias. This work shows both the potential and the limits of machine learning for informing sustainable grassland management and explainability thereof. Frequent mowing and higher mineral nitrogen inputs explained most of the predictable variation, enabling a 76% accurate separation of low and high biomass categories. Predictive accuracy fell below 60% for finer class resolutions, indicating that management records alone are insufficient for detailed yield forecasts without complementary environmental data.

Nitrous oxide is a potent greenhouse gas due to its long atmospheric lifespan (121 years) that results in a high global warming potential (GWP). Research has shown that no-tillage may be implemented as a mitigation strategy to reduce N2O emissions. The objective of the was to evaluate how conventional tillage (CT) and no-tillage (NT) can potential influence N2O emissions in soybean rotation in a semi-arid region of the central Free State of South Africa. The effect of conventional and no-till tillage practices on N2O emissions under soybean rotation was evaluated in the 3rd year of a 5-year rotation system, in a semi-arid region of the Free State of South Africa, from December 2022 to December 2023. The experimental area was divided into three blocks and there were two plots in each block: in total there were six plots. The treatments were planted in a soybean rotation system under no-tillage and conventional tillage. The monthly averages of N2O emissions were significantly different from each other during the soybean growing season; the highest emissions were recorded in August/September 2023 from both the NT and CT treatments after harvest. During this time, there were crop residues in the soil that increased soil carbon. There was a positive correlation between N2O emissions and soil carbon content (p = 0.21) and between N2O emissions and soil organic matter (p = 0.43). Emissions were significantly higher in CT (LSD = 0.3) than in NT. The lowest N2O emissions were recorded in December 2023 (LSD = 0.05) and were significantly reduced in the no-till plots compared to those of the conventional tillage plots. Furthermore, the lowest cumulative N2O emissions of 0.26 ± 0.22 kg N2O-N ha−1 were recorded during NT in the winter season and were significantly different from CT (LSD = 0.19). The results from our study indicate that the no-till practices in soybean rotation can decrease N2O emissions.

Monoculture systems depend on high nitrogen (N) fertilisation. Incorporating legumes into forage crops offers a sustainable alternative with agronomic and economic benefits. This study assesses the impact of legumes in fodder systems, evaluating yield, N use efficiency (NUE), and profitability while identifying the best cropping strategy under semi-arid conditions. The experiment, conducted at Herdade da Comenda, Elvas, Portugal, used a split–split-plot randomised block design to analyse N doses, forage species, and irrigation. Economic metrics, including costs, net revenue, return on investment, and risk analysis, were also assessed. Moderate N doses (120 kg ha−1) resulted in significantly higher NUE (15.67 kg kg−1 N) than higher doses (200 kg ha−1), which yield only 1.40 kg kg−1 N (p < 0.05), particularly in mixed fodder crops. Irrigation improved N absorption, crop nutrition, and yield, leading to higher profitability despite increased initial costs. Agronomically, irrigation and N doses influenced yield and nutrient uptake, while no significant differences were observed between different forage crops in terms of yield or NUE. Economically, the irrigated mixed crop showed the highest return on investment (ROI = 247.37 EUR ha−1), whereas ryegrass presented lower financial risk (BE = 2213.24 kg ha−1) due to lower establishment costs. Yield was the strongest predictor of net profit (R2 = 0.89). Looking ahead, optimising N management, irrigation strategies, and mixed grass–legume crops will be crucial to maximising economic returns while minimising environmental impacts.

In Spain, several major cities face high rates of avoidable deaths due to NO2 exposure. Understanding NO2 atmospheric dynamics is essential to support public health efforts and policymaking. Recent satellite products have proven useful in characterizing urban atmospheric composition in various regions. This study compares NO2 concentration data from in situ air quality monitoring networks and the Sentinel-5P TROPOMI satellite in Spain’s three largest cities (Madrid, Barcelona, and Valencia), alongside O3 levels —due to its close photochemical relationship with NOx—wind speed and direction, temperature, relative humidity, and solar radiation. Data from 2022 were analyzed using Pearson correlation coefficients and Principal Component Analysis (PCA) to identify key relationships and patterns. Results showed a consistent negative correlation between NO2 and O3, wind speed, temperature, and solar radiation. Differences between in situ and satellite data were more pronounced in coastal cities, influenced by wind patterns and urban morphology (Madrid: r = 0.86, v = 1.34 m/s; Valencia: r = 0.68, v = 2.97 m/s; Barcelona: r = 0.65, v = 8.04 m/s). These insights enhance the understanding of NO2 behavior in urban environments and support the use of remote sensing to estimate surface-level pollution in areas lacking ground-based monitoring infrastructure. This is the first study in Spain to jointly evaluate NO2 from satellite and in situ data across multiple cities, linking pollutant concentrations with meteorological and chemical drivers to improve surface-level estimation strategies and support air quality assessment in under-monitored areas.

Alley cropping, an agroforestry system that integrates trees and arable crops, holds the potential to improve both crop yields and soil health. It has been found to be effective for upland crops in many countries of the world. However, the utilization of alley cropping to improve soil health in the terrace ecosystem of Bangladesh is poorly understood. Therefore, this study was undertaken to assess the changes in soil biochemical properties and quantify the cabbage yield under three alley widths of Leucaena leucocephala (3.0, 4.5, and 6.0 m size) and five nitrogen (N) levels [0, 40, 80, 120, and 160 kg N ha−1 (0, 25, 50, 75, and 100% of recommended N rates, respectively) with the addition of pruned materials of L. leucocephala (Ipil-ipil)]. The field experiment was conducted following a split-plot design, where alley width was considered as the main-plot factor and N rate as the sub-plot factor. Within each main plot, the five N rates were replicated thrice. Control plots with similar N doses were applied accordingly without addition of pruned materials to compare the results with alley cropping. Data were collected on the biochemical properties of the soil [soil pH, organic carbon (C), total N, available phosphorus (P), exchangeable potassium (K), microbial biomass C, and biomass N] and the yield of cabbage quantified [edible head weight (kg plant−1) and head yield (t ha−1)] under different alley widths and control. Findings revealed that organic C, total N, available P, exchangeable K, microbial biomass C, and biomass N in the topsoil exhibited maximum values in the L. leucocephala-based alley plot, which is proved to be a possible solution of restoration of degradable land. Additionally, L. leucocephala-based alley cropping improved the soil pH, indicating a potential avenue for more-sustainable land management practices. Results also showed that alley widths and N rates have significant effects on cabbage (Brassica oleracea L. var. capitata) yield. Alley width of 6.0 m along with 100% N provided the highest cabbage yield followed by 75% N in 6.0 m alley, and the control with 100%. The wider alley minimizes tree–crop competition, allowing for optimal cabbage production. These aforementioned results suggest that alley cropping with L. leucocephala is a promising approach to enhance soil fertility and crop productivity in the terrace ecosystem of Bangladesh.

An experiment was conducted in spring 2024 to investigate the effects of biochar, biogas slurry, and dicyandiamide (DCD) on N2O emissions from soil in protected tomato cultivation. Five treatments were applied: conventional fertilization (CK1), biogas slurry alone (CK2), biochar combined with biogas slurry (T1), DCD combined with biogas slurry (T2), and the combination of biochar, biogas slurry, and DCD (T3). The study aimed to assess the response of the soil physicochemical properties and nitrifying ammonia-oxidizing microorganisms in the tomato root zone to these treatments and to determine their impact on soil N2O emissions. The results showed that adding biochar and biogas slurry increased the soil pH, organic matter content, and levels of nitrate-N and ammonium-N, without affecting ammonia-oxidizing archaea (AOA) but inhibiting ammonia-oxidizing bacteria (AOB). The inclusion of DCD raised the soil pH and ammonium-N levels, enhanced AOA growth, did not alter organic matter content, and significantly reduced nitrate-N levels and AOB activity. Compared to CK1, treatments CK2, T1, T2, and T3 decreased the average N2O emission flux by 5.83%, 8.24%, 15.27%, and 16.16%, respectively. The application of biochar, biogas slurry, and DCD enhanced the physicochemical properties of the root zone soil and notably reduced N2O emissions in protected tomato cultivation, with T3 showing the most effective results. The biochar and biogas slurry used in this study, both derived from agricultural waste, promote sustainable agricultural development and enhance economic benefits. However, this study only considered the short-term effects of biochar, biogas slurry, and DCD, necessitating further research to explore their long-term impacts and mechanisms.