Use of soil cover crops of different families in crop rotation or succession under no-tillage system (NTS) for onion production results in higher soil quality compared to land use systems with less plant diversity. The objective was to evaluate the effect of using different combinations of plant species from different botanical families in rotation and succession of soil cover crops in NTS for onion production on formation of macroaggregates, mesoaggregates, and microaggregates, and on total organic C (TOC) and N (TN) contents, including isotopic forms of C and N, in soil aggregates and bulk soil. The treatments (T) evaluated were maize/onion (NTS-T1); cover plants (winter)/onion (NTS-T2); maize/winter grasses/onion (NTS-T3); velvet bean/onion (NTS-T4); millet/cover plants (winter)/onion (NTS-T5); velvet bean/rye/onion (NTS-T6); maize/onion in conventional tillage system (CTS-T7); and intercrop cover plants (summer)/onion (NTS-T8). We evaluated macroaggregates (8.0–0.25 mm), microaggregates (<0.25 mm), and bulk soil (<2.0 mm) at depths of 0–5, 5–10, and 10–20 cm, in a nine-year field experiment. The greater plant diversity in T2–T6 and T8 resulted in higher geometric mean diameter (GMD) of aggregates compared to T1 and T7. The T8 was more efficient in increasing GMD in the 10–20 cm soil depth than the other treatments. The T1 was more efficient in improving the evaluated soil physical and chemical attributes than T7. The use of NTS with plants of the Poaceae and Fabaceae families in single or intercrop systems for onion production resulted in higher TOC and TN contents in the 0–5 and 5–10 cm soil depths compared to CTS. Isotope 15N measurements showed that C and N were more protected in microaggregates in all evaluated treatments and depths compared to macroaggregates and bulk soil. Macroaggregates had more TOC and TN than microaggregates.

Onion (Allium cepa L.) is a food crop of economic importance. In Brazil, the crop typically occurs in a conventional tillage system (CT), which favors the mineralization and decomposition of soil organic matter (SOM) and the loss of carbon (C) and nitrogen (N). On the other hand, the no-tillage vegetable system (NTVS) operates based on sustainable pillars and bypasses the adverse effects of CT. This study evaluated the total C and N stocks and particle-size fractions of SOM in NTVS with single and intercropped cover plants compared to vegetable crops under CT. The NTVS evaluated treatments were as follows: (1) spontaneous vegetation (SV); (2) black oats (BO); (3) rye (RY); (4) oilseed radish (OR); (5) RY + OR; and (6) BO + OR. A treatment under CT with millet cover, a no-tillage system with (NTS) millet + velvet + sunflower cover, and a forested area as the original condition was also evaluated. Soil samples were collected in 0–5, 5–10, and 10–30 cm layers. Stocks of total organic C (TOC), total N (TN), particulate OC (POC), particulate N (PN), mineral-associated OC (MAOC), and mineral-associated N (MN) were evaluated. The highest stocks of TOC, TN, POC, and NM were found in NTVS compared to CT, and RY + OR showed the best results. The NTVS showed higher TOC and TN stocks with grasses and cruciferous intercropped than NTVS with SV and CT. POC and PN stocks increased in areas with single and intercropped RY and OR treatments. MAOC and MN stocks were higher than forest in RY + OR intercrop in the topsoil layer. RY and OR intercrop efficiently added C and N to the soil under NTVS. The consortium of millet + velvet + sunflower in NTS showed higher TOC, TN, POC, and PN stocks compared to the other treatments (0–5 and 0–30 cm). In general, the intercrop of cover plants is ideal for obtaining the NTVS maximum potential, favoring several mechanisms between soil, plant, and atmosphere, resulting in improved soil quality, increased organic matter, and higher stocks of C and N.

O trabalho objetivou avaliar as propriedades químicas e os estoques de carbono (C) e de nitrogênio (N) do solo sob cultivo de cebola por 16 anos, no sistema de plantio direto de hortaliças (SPDH), comparado com o sistema de preparo convencional (SPC) e o sistema de plantio direto (SPD). O delineamento experimental foi em blocos ao acaso com quatro repetições e três tratamentos: SPD - sucessão milho/cebola anual; SPC - sucessão milho/cebola anual; SPDH - consórcio mucuna+milheto+girassol e cebola anual. Amostras de solo foram coletadas nas profundidades de 0-5 cm, 5-10 cm e 10-30 cm para avaliação dos atributos químicos do solo e dos estoques de C e N. Não foram verificadas diferenças de pH e de densidade do solo entre os tratamentos. O SPDH apresentou maiores teores de potássio entre 10 e 30 cm. Para o fósforo, o SPDH e o SPD apresentaram os maiores valores nos intervalos de 0-5 e 5-10 cm. O SPDH tem maior potencial para armazenar C e N em comparação com os demais tratamentos. O consórcio de plantas de cobertura no SPDH é eficaz para aumentar os teores de potássio em profundidade, bem como promover maiores teores e estoques de C e N em comparação aos tratamentos SPD e SPC. Palavras-chave: sistema de plantio direto de hortaliças; ciclagem de nutrientes; consórcio de plantas de cobertura; acúmulo de carbono. Total carbon and nitrogen stocks and soil chemical properties in onion production The study aimed to evaluate soil chemical properties and carbon (C) and nitrogen (N) stocks after 16 years of onion cultivation in the no-till vegetable system (SPDH) compared with the conventional tillage system (SPC) and the no-till system (SPD). The experimental design was a randomized block with four replicates and three treatments: SPD (annual maize/onion rotation), SPC (annual maize/onion rotation), and SPDH (a mix of velvet bean, pearl millet, and sunflower intercropped with annual onion). Soil samples were collected at depths of 0–5 cm, 5–10 cm, and 10–30 cm to assess chemical properties and C and N stocks. No significant differences were observed for soil pH or bulk density among treatments. The SPDH showed higher potassium levels at 10–30 cm. For phosphorus, SPDH and SPD had the highest values at 0–5 cm and 5–10 cm depths. SPDH demonstrated a greater capacity for storing C and N compared to the other treatments. The plant cover mix in SPDH proved effective in increasing potassium at deeper soil layers and enhancing C and N levels and stocks relative to SPD and SPC treatments. Keywords: no-tillage vegetable system; nutrient cycling; cover crop consortium; carbon accumulation.

Efeito da sucessão ou rotação de culturas sobre a fertilidade do solo após sete anos de cultivo com cebola / Effect of crop succession or rotation on soil fertility after seven years of onion cultivation

Objective: The objective of this work was to evaluate the total carbon (C) and nitrogen (N) contents and the granulometric fractions of soil organic matter (SOM) under different management systems with single and intercropped winter cover crops in the cultivation of onion in Ituporanga, SC. Theoretical framework: Onion cultivation typically occurs in a conventional tillage system (CTC), which favors the loss of C and N from the soil due to soil mobilization. The vegetable no-tillage system (VNTS) uses sustainable practices with continuous soil cover and restricted soil tillage, promoting improvement of edaphic attributes. Methodology: The experiment was implemented in 2009 and the collection of soil samples took place in 2019 in the layers of 0-5, 5-10 and 10-30 cm in the treatments under VNTS, being black oat (AV); rye (CE); oilseed radish (NB); rye + radish (CE+NB); black oat + oilseed radish (AV+NB) and spontaneous vegetation (VE). In addition to these treatments, two adjacent areas were used, one under CTS and the other in a secondary forest area (MATA). The content of total organic C (TOC), total N (NT), light organic matter in water (LOM), particulate organic carbon (POC), particulate nitrogen (PN), C associated with minerals (COam) and N associated with to minerals (NAM). Results and conclusions: VNTS increased TOC and NT contents with the use of grass and cruciferous intercropping to the detriment of single crops and CTS. The LOM content was higher in VNTS with the use of single grasses and stood out in relation to VNTS with consortium. There were no differences for PN between MATA, CE and CE+NB, demonstrating that VNTS is efficient in raising these levels in substitution of CTS. The CE+NB consortium increased the levels of COam and NAM in the surface layer of the soil after replacing CTS with VNTS. Research implications: In VNTS, the use of intercropping between cover crops is an efficient management in adding C and N to the soil, as the simultaneous cultivation of different species of cover crops produces straw with an intermediate C/N ratio, the roots exploit different soil extracts and nutrient cycling is more efficient. Originality/Value: The results of this study are from a long-term experiment (10 years), which demonstrates the effectiveness of VNTS in recovering and increasing C and N levels in soil previously cultivated for a long period in the CTS, in addition to to match the forest area.

Vegetable production primarily relies on the conventional tillage system (CTS), which leads to soil degradation through erosion and reduced soil health. The use of no-tillage vegetable systems (NTVS) aims to mitigate these issues; however, information about the impact of this management system on soil health and greenhouse gas (GHG) emissions remains limited. Thus, the objective of this study was to conduct an on-farm evaluation of the effects of no-tillage and cover crop use on soil C and N contents and stocks, soil bulk density (SD), mean geometric diameter (MGD) of aggregates, soil temperature, volumetric soil moisture (VM), plant yield, and GHG emissions in cauliflower production under NTVS compared to CTS in a subtropical ecosystem in southeastern Brazil. Chemical and physical properties were assessed at depths of 0–5, 5–10, and 10–30 cm. GHG emissions, particularly nitrous oxide (N₂O), carbon dioxide (CO₂), and methane (CH₄) were measured using closed static chambers and gas chromatography. NTVS with cover crop mixes had higher yield than CTS without cover crops (25.1 and 18.4 Mg ha⁻¹, respectively). NTVS exhibited increased MGD and VM and reduced SD. Soil temperature in the 0–5 cm layer was lower in NTVS than in CTS. Soil C and N stocks were higher in NTVS, but high N₂O emissions offset this advantage compared to CTS. Overall, NTVS emitted more CO₂ and N₂O than CTS, while both systems showed soil CH₄ uptake. NTVS maintained sufficient carbon equivalent reserves (0–30 cm) to offset GHG emissions, making it a viable alternative for plant yield and soil quality; however, its environmental impact on GHG emissions requires further attention.