The use of plant species in rotation or succession of crops can increase C and N contents and their fractions in the soil. The objective of this study was to evaluate the effect of using soil cover crops in succession and rotation with onion crops in different soil management systems on the total organic carbon (TOC), total nitrogen (TN), and C and N fractions in soil aggregates, and bulk soil. The experiment was implemented in April 2007 with eight treatments: succession of onion and maize in a no-tillage system (NTS) (T1); rotation of soil cover crops (winter) and biennial onion in a NTS (T2); rotation of maize, winter grasses, and onion in a NTS (T3); succession of summer legume and annual onion in a NTS (T4); rotation of summer grass, winter grasses, and annual onion in a NTS (T5); succession of summer legume, winter grass, and annual onion in a NTS (T6); succession of maize and onion in a conventional tillage system (CTS) (T7); and succession of intercrops of soil cover crops (summer), and annual onion in a NTS (T8). Undisturbed soil samples were collected in the 0.0–5.0, 5.0–10.0, and 10.0–20.0cm soil layers in July 2014, and their aggregate (8.0 to 2.0mm) and bulk soil (<2mm) fractions were separated to evaluate their TOC, TN, particulate organic carbon and particulate organic nitrogen (OCP and ONP respectively), and mineral-associated organic carbon and mineral-associated organic nitrogen (OCM and ONM respectively). Soil turning due to the CTS in T7 (0.0–5.0cm) reduced TOC, OCP, OCM, TN, ONP, and ONM, in the soil aggregates and in the bulk soil, when compared with the NTS with the use of soil cover crops in succession or rotation with onion crops (T1–T6 and T8). T6 increased the TOC, TN, OCP, OCM, ONP, and ONM contents in the soil aggregates and bulk soil when compared with the successions with only grasses or only legumes. T1 increased the soil TOC and TN contents in aggregates compared with the same succession in CTS. T8 had higher OCP (0.0–20.0cm) and ONP (5.0–10.0cm) contents in aggregates than in the bulk soil. In general, aggregates had higher TOC and OCM contents, and bulk soil had higher TN, OCP, ONP and ONM contents. The main changes resulting from the management systems and soil cover crop combinations used were observed in the particulate fraction, especially in the soil aggregates.

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.

Aplicações sucessivas de dejetos suínos podem promover mudanças nos atributos físicos do solo, com ênfase nas vias de formação dos agregados solo. O objetivo deste trabalho foi separar e quantificar os agregados conforme sua via de formação e avaliar a estabilidade desses agregados em área com histórico de aplicações de dejeto líquido de suínos (DLS) e cama sobreposta de suínos (CSS), em sistema plantio direto (SPD). Após 10 anos do uso de dejetos suínos (DS) na sucessão aveia/milho sob SPD, coletaram-se amostras indeformadas de solo nas camadas de 0-5 e 5-10 cm, nos tratamentos sem DS (testemunha), com aplicação de DLS e CSS em doses equivalentes a uma e duas vezes a recomendação de N para o milho e a aveia (DLS1X, DLS2X, CSS1X e CSS2X, respectivamente). Os agregados foram separados conforme os seus padrões morfológicos e vias de formação em biogênicos e fisiogênicos. Em seguida, avaliaram-se o diâmetro médio ponderado (DMP) dos agregados e a distribuição dos agregados nas classes de diâmetro para macroagregados (8,00 > Ø ≥ 2,0mm), mesoagregados (2,0 > Ø ≥ 0,25mm) e microagregados (Ø < 0,25mm), em cada tipo de agregado. A adição de dejetos suínos aumentou a formação de agregados biogênicos. Na área testemunha prevalece a via de formação de agregados fisiogênicos. A aplicação de DLS não alterou o DMP e os macroagregados em relação à testemunha, enquanto a aplicação de CSS aumentou esses parâmetros quando comparada aos tratamentos DLS e Testemunha.

The conversion of conventional tillage system (CTS) into no-tillage system (NTS) for onion crops with use of soil cover crops increases carbon and nitrogen contents in the soil aggregates. The objective of this work was to evaluate the effects of combinations of different plant species and soil management systems using rotation with soil cover crops for onion crops on the light organic matter (LOM), carbon (C), and nitrogen (N) contents in the organic matter granulometric fractions in soil macroaggregates and bulk soil. A nine-year experiment (2007-2016) was conducted using the treatments (T): maize-onion in NTS (T1); soil cover crops (winter)-onion in NTS(T2); maize-winter grasses-onion in NTS (T3); velvet bean-onion in NTS (T4); millet-soil cover crops (winter)-onion in NTS (T5); velvet bean-rye-onion in NTS (T6); maize-onion in CTS (T7); intercropped soil cover crops (summer)-onion in NTS (T8). C and N contents in the LOM, particulate organic C and N (POC and PON), and mineral- associated C and N (MOC and MON) were evaluated in soil macroaggregates (8.0 to 2.0 mm) and bulk soil (<2.0 mm) from the 0–5 cm, 5–10 cm, and 10–20 cm layers. High diversity and combinations of plant species in T2-T6, and T8 resulted in higher POC and MON contents in aggregates, and higher MOC and PON contents in bulk soil, when compared to T1 and T7. T2 was a better option to increase LOM and POC contents in aggregates (0-5 cm). The evaluation of POC (0–5 cm), PON, and MON (0-10 cm) contents in soil aggregates showed more significant differences between the treatments than the contents found in bulk soil. The onion crops under NTS combined with use of rotations with soil cover crops were more efficient to improve the evaluated soil attributes than those under CTS.

Espécies vegetais de diferentes famílias na rotação ou sucessão de culturas para o cultivo de cebola podem melhorar os atributos químicos do solo. Avaliou-se os efeitos do cultivo de diferentes espécies de plantas de cobertura sobre os atributos químicos do solo no cultivo da cebola em sistema plantio direto (SPD) e convencional do solo (SPC). Os tratamentos foram: T1-sucessão cebola/milho em SPD; T2-rotação comercial com cobertura de inverno em SPD; T3-rotação milho/gramíneas de inverno em SPD; T4-sucessão leguminosa de verão em SPD; T5-rotação gramíneas de verão/inverno em SPD; T6-sucessão leguminosa de verão/gramínea inverno em SPD; T7-sucessão milho/cebola em SPC; T8-consórcio de coberturas de verão em SPD. Foram quantificados os teores de carbono orgânico total (COT), nitrogênio total (NT), e parâmetros de fertilidade. Calculou-se a capacidade de troca catiônica (CTC). O revolvimento do solo e a sucessão milho/cebola em SPC (T7) reduz os teores de COT e NT quando comparado ao SPD com o uso de plantas de cobertura em sucessão e rotação com a cebola. O uso de mucuna preta (leguminosa) e centeio (gramínea) em sucessão à cebola (T6) aumenta os teores de COT e NT quando comparado com a rotação ou sucessão com somente gramíneas ou somente leguminosas. A sucessão cebola/milho no SPD (T1) e no SPC (T7) apresentam resultados contrastantes: o SPD na sucessão milho/cebola aumenta os teores de COT, NT, Ca e CTC na camada superficial do solo em comparação ao SPC. A rotação de gramíneas no verão (milheto) e no inverno (aveia e centeio) para produção de cebola no SPD aumenta os teores de Ca e a CTC do solo em profundidade (5-10 e 10-20 cm), sendo mais eficientes que os demais tratamentos. O uso de mucuna preta (leguminosa) e centeio (gramínea) em sucessão a cebola (T6) incrementa os atributos químicos do solo na camada superficial em comparação aos tratamentos com ausências de plantas de coberturas (T1 e T7).

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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.