The complex ramifications of global climate change, which is caused by heightened concentrations of greenhouse gases in the Earth’s atmosphere, are deeply concerning. Addressing this crisis necessitates the immediate implementation of adaptive mitigation strategies, especially within the agricultural sector. In this context, this study aimed to assess how the supply of nitrogen (N) (0, 70, 140, and 210 kg N ha⁻¹) in the forms of ammonium nitrate and urea affects the agronomic performance, food quality, greenhouse gas emissions (GHG), and carbon footprint of potato plants. The examined hypothesis was that by precisely calibrating N doses alongside appropriate sourcing, over-fertilization in potato cultivation can be mitigated. A decline in stomatal conductance and net photosynthetic rate disturbs physiological mechanisms, reflecting in biomass production. Application of 136 kg N ha⁻¹ as urea showed a remarkable yield increase compared to other doses and sources. The highest nitrate content in potato tubers was achieved at 210 kg N ha⁻¹ for both sources, not exceeding the limit (200 mg kg⁻¹ of fresh mass) recommended for human consumption. The lowest carbon footprint was obtained when 70 kg N ha⁻¹ was applied, around 41% and 26% lower than when 210 kg N ha⁻¹ and 140 kg N ha⁻¹ were applied, respectively. The results demonstrated that over-fertilization not only worsened the yield and tuber quality of potato plants, but also increased greenhouse gas emissions. This information is valuable for establishing an effective fertilization program for the potato crop and reducing carbon footprint.

Cover crops and N fertilization strongly impact the forms of soil organic C and N and their availability, which change the responses of plants to N fertilization and soil organic C accumulation. Our study objectives were to evaluate the effects of cover crops and N doses on soil total and soluble C and N contents, N fractions, and potentially available N in a long-term no-till experiment. The experiment was conducted in a randomized block design with split plots and four replicates. The main treatments were cover crops species, jack bean, lablab bean, millet, velvet bean, and fallow cultivated prior to maize. Secondary treatments included two doses of mineral N (0 and 120 kg ha⁻¹). Soil samples were collected at depths of 0–5, 5–10, 10–20, and 20–40 cm, which were analyzed for total and water-soluble C and N contents, N fractions (acid hydrolysis method), and potentially available N (hot KCl solution and direct steam distillation methods). Cover crop velvet bean resulted in the highest soil organic carbon levels, and cover crop millet plus fertilization resulted in the highest levels of soil total N. The amino sugar was the largest N fraction, which decreased by 8% with N fertilization. The soluble C and N content strongly correlated with total and available N content. The changes in soil N were influenced by cover crop species and fertilization and the interactions of both, so the combination of fertilization regime and cover crops must be chosen with care. Additionally, legumes are a good source of plant and soil N in systems with low input of N via fertilizer; however, the combination of N fertilizer with legumes can reduce soil N reserves, leading to its long-term depletion.

Maize (Zea mays L.) is a crop widely cultivated in the state of São Paulo, and the sustainable management of nitrogen (N) nutrition is crucial to improving productivity and the environment, which calls for a reliable means of predicting potentially available soil N. A study was undertaken to evaluate and compare biological and chemical indices of potential N availability for a diverse set of 17 soils collected in the northwest region of São Paulo state. For this purpose, mineralization assays were performed at three distinct temperatures, and chemical assessments were carried out using the Illinois Soil Nitrogen Test (ISNT) and by fractionation of hydrolysable soil N. In addition, a greenhouse experiment was conducted to determine dry matter and N accumulation in the aboveground parts of maize plants. Potentially available N estimated by the incubation methods increased with increasing temperature and was strongly correlated with N uptake (r = 0.90). Hydrolysable N fractions varied widely among the soils studied and were more variable for amino sugar N than for other fractions. Potentially available N estimated by the ISNT was highly correlated with hydrolysable amino acid N and amino sugar N (r = 0.95–0.96) and also with plant dry matter accumulation (r = 0.82) and N uptake (r = 0.93). The ISNT has potential to improve fertilizer N recommendations for maize production in Brazil, provided that the test values are interpreted relative to an appropriate calibration database, planting density, and other factors affecting crop N requirement.

Estimating mineralization rates is one of the best ways to predict N availability over time. However, different methods can lead to distinct predictions, especially when different production systems are used. The aim of this study was to compare biological and chemical methods commonly used to estimate the potentially available N in a soil cultivated with maize in succession to cover crops and N fertilization. The experimental area has been cultivated with cover crops (jack bean, velvet bean, millet and spontaneous vegetation) and N fertilization (0, 60, 120 and 180 kg N ha⁻¹) since the year 2000 in a split-plot design with cover crops as the main treatments and N rates as secondary treatments. The biological evaluation of N mineralization was performed by means of an aerobic incubation of soil samples, while the chemical methods were either by the use of saline ((Ca(H₂PO4)₂, CaCl₂, KCl) and Illinois soil test and direct steam distillation (DSD). Soil C and N contents were not affected by the cover crops, even after sixteen years of cultivation. The utilization of N by maize plants was affected by cover crops, especially for jack bean, while N fertilization led to a maximum absorption point, estimated in 158 kg N ha⁻¹. The methods for evaluating the potentially available N behaved differently among treatments. The DSD method has significantly correlated with maize N uptake and yield, which demonstrates that it was the most promising method to estimate the potentially available N, although it is not yet calibrated for all agricultural systems.

Foram realizados dois experimentos em casa de vegetação para avaliar o efeito da adição de um vermicomposto oriundo de lixo urbano e da calagem na matéria seca e na concentração de metais pesados na parte aérea de plantas de alface cv. Mesa 659. Em um dos ensaios, foi usado um Latossolo Vermelho distroférrico e, em outro, um Argissolo Vermelho-Amarelo eutrófico. O delineamento experimental de cada experimento foi em blocos ao acaso, em esquema fatorial 5 x 5, com quatro repetições, combinando-se calagem para elevar a saturação por bases a 40; 50; 60; 70 e 80%, e o equivalente a 0; 25; 50; 75 e 100 t ha-1 de vermicomposto. Uma única aplicação de vermicomposto de lixo urbano, em doses acima de 50 t ha-1, limitou a produção de alface nos dois tipos de solos. Mesmo estas doses que restringiram a produção da alface, não a tornaram imprópria para consumo humano do ponto de vista da concentração de metais pesados.

Traditional farming practices are highly dependent on chemical fertilizers, which might deteriorate soils when used in the long term. In face of the increasing generation of biodegradable materials worldwide, the adoption of technologies that harvest nutrients from waste complies with the concepts of a circular economy. This study evaluated the effects of a compost prepared with biodegradable waste from the aquaculture industry, when applied in a Brazilian latosol, for its fertility traits, growth of maize plants and the soil basal respiration over time. The compost was applied to the soil and evaluated at 0, 30, 60, 90 and 120 days. Soil organic matter increased by an average of 4 g dm⁻³ after 30–120 days of incubation, and soil fertility was generally increased, especially regarding the concentration of N, P, and micronutrients. Maize plants grew approximately 60% larger in the presence of the waste-based compost, in comparison to the control, and displayed higher concentration of nutrients. In addition, CO₂ and NH₃ emissions slightly increased when the compost was applied, indicating an advanced degree of stability of the organic soil amendment.