ABSTRACT Carbon (C) and nitrogen (N) content in granulometric fractions of soil organic matter (SOM) are sensitive indicators of soil quality changes caused by management systems. This study evaluated the C and N content in granulometric fractions of SOM of aggregates, an Inceptisol under onion grown in no-till vegetable farming systems (NTVFS) and conventional tillage systems (CTS), comparing them to a secondary forest. Treatments consisted of soil cover crops, monocropped and intercropped with onions grown under NTVFS: spontaneous vegetation, 100% black oats; 100% rye; 100% oilseed radish; oilseed (14%) + rye (86%) intercrop and oilseed (14%) + oats (86%) intercrop. The same evaluations were also performed in an area with onions grown under CTS for ± 37 years, and in secondary forest (± 30 years). Undeformed soil samples were collected from 0-5, 5-10, and 10-20 cm deep soil layers, and aggregates were subsequently separated (8.00 mm > Ø ≥ 2.0 mm). Organic C (OC) and N of the granulometric fractions contents were quantified in aggregates, which were subdivided into particulate fractions (POC and PN) and mineral-associated fractions (OCam and Nam). NTVFS promoted protection of SOM at the 0-5 cm depth compared to CTS, as a result of higher POC content. Intercropped oats+oilseed and spontaneous vegetation contributed to an increase in PN content compared to all other treatments under NTVFS. Monocropped and intercroppped oilseed radish caused an increase in Nam, which was more effective than OCam to indicate differences among the systems. Conversion of areas from CTS to NTVFS promotes increases in POC and PN content in the upper soil layer. NTVFS improves the quality of aggregates, and it may reduce damage caused by CTS.

RESUMEN El contenido de carbono (C) y nitrógeno (N) en las fracciones granulométricas de la materia orgánica del suelo (MOS) es un indicador sensible de los cambios en la calidad del suelo causados por los sistemas de manejo. Este estudio evaluó el contenido de Cy N en fracciones granulométricas de la MOS de agregados, en un Inceptisol bajo cebolla cultivada en sistema de cultivo de vegetales sin labranza (SCVSL) y sistema de labranza convencional (SLC), comparándolos con un bosque secundario. Los tratamientos consistieron en cultivos de cobertura del suelo, monocultivos y consorciados con cebollas cultivadas bajo SCVSL: vegetación espontánea, 100% de avena negra; 100% de centeno; 100% nabo forrajero; consorcio de nabo (14%) + centeno (86%), consorcio de nabo (14%) + avena (86%). Las mismas evaluaciones se realizaron en un área con cebollas cultivadas bajo SLC durante ± 37 años, y en un bosque secundario (± 30 años). Se recogieron muestras de suelo no deformadas de capas de suelo de 0-5, 5-10 y 10-20 cm de profundidad, y los agregados se separaron posteriormente (8.00 mm> Ø ≥ 2.0 mm). Las cantidades de C orgánico (CO) y N de las fracciones granulométricas se cuantificaron en agregados, que se subdividieron en fracciones particuladas (PCO y PN) y fracciones asociadas con minerales (COam y Nam). SCVSL promovió la protección de MOS a una profundidad de 0-5 cm en comparación con SLC, como resultado de un mayor contenido de POC. La avena consorciada con nabo y la vegetación espontánea contribuyeron a un aumento en el contenido de PN en comparación con todos los otros tratamientos bajo SCVSL. El nabo forrajero en monocultivo y consorciado causó un aumento en Nam, que fue más efectivo que el COam para indicar diferencias entre los sistemas. La conversión de áreas de SLC a SCVSL promueve aumentos en el contenido de PCO y PN en la capa superior del suelo. SCVSL mejora la calidad de los agregados, y puede reducir el daño causado por SLC.

ABSTRACT Carbon (C) contents of humic substances (HS) in soil aggregates are a sensitive indicator of changes in the edaphic quality caused by soil management systems and/or cover plant species. The aim of this study was to assess total contents of C and HS of organic matter in soil aggregates cultivated with onion under a no-till vegetable production system (NTVS) and conventional tillage (CT) compared to a secondary forest area. Treatments consisted of single and mixed cover crops and onion under NTVS: spontaneous vegetation, 100% black oat; 100% rye; 100% oilseed radish; consortium of oilseed radish (14%) + rye (86%); consortium of oilseed radish (14%) + black oat (86%). An area cultivated with onion under CT (± 37 years) and a forest area (secondary forest; ± 30 years) were also evaluated. Five years after implementation of NTVS, undisturbed soil specimens were collected from the 0.0-0.05, 0.05-0.10 and 0.10-0.20 m layers and aggregates were obtained (8.00 mm > Ø > 2.0 mm). In tríese aggregates, total organic carbon (TOC) and C of HS were determined, subdividided into a fulvic acid fraction (C-FAF), humic acid fraction (C-HAF) and humin (C-HUM). With the C values of the HS the following ratios were calculated: C-HAF/C-FAF and (C-HAF+C-FAF)/C-HUM. The highest content of TOC, C-FAF, C-HAF and C-HUM were found in the forest. In NTVS, the contents of TOC (at the 0.0-0.05 m depth) and C-HUM (0.0-0.05 and 0.05-0.10 m) were higher than those found under CT. The highest C-FAF contents were found under CT. NTVS compared to CT favors the humification process (higher C-HUM content and lower ratios of C-HAF+C-FAF/C-HUM (at the 0.0-0.05 and 0.05-0.10 m depths) and the protection of organic matter (higher TOC contents at the 0.0-0.05 m depth)). A linear relationship was observed between C-HUM and N of HS. Among the cover plant species, rye alone and rye combined with oilseed radish had the best results regarding humification of organic matter with predominance of C-HUM and C-HAF. This pattern was also observed in the control for C-HUM, due to the abundance of plant families and species, indicating that plant biodiversification is an effective way to improve the quality of soil.

RESUMEN Los contenidos de carbono (C) de las sustancias húmicas (SH) en los agregados del suelo son un indicador sensible de los cambios en la calidad edáfica causados por los sistemas de manejo del suelo y / o las especies vegetales de cobertura. El objetivo de este estudio fue evaluar el contenido total de C y SH de materia orgánica en agregados de suelo cultivado con cebolla bajo sistema de siembra directa de hortalizas (SSDH) y sistema de preparación convencional (SPC), comparando con un área de bosque. Los tratamientos consistieron en cultivos de cobertura solos y asociados con cebolla bajo SSDH: vegetación espontánea, 100% avena negra; 100% centeno; 100% nabo forrajero; consorcio de nabo (14%) + centeno (86%); consorcio de nabo (14%) + avena negra (86%). También se evaluó un área cultivada con cebolla bajo SPC (± 37 años) y un área de bosque (bosque secundario, ± 30 años). Cinco años después de la implementación de SSDH, se escogieron muestras de suelo de las capas 0,0-0,05, 0,05-0.10 y 0,10-0,20 my obtenidos los agregados (8.00 > Ø > 2,0 mm). En estos agregados, se determinaron el carbono orgánico total (COT) y C de SH, subdivididos en fracción ácido fúlvico (C-FAF), fracción ácido húmico (C-FAH) y humin (C-HUM). Con los valores de C de las SH, se calcularon las siguientes proporciones: C-FAH/C- FAF y (C-FAH + C-FAF)/C- HUM. El mayor contenido de COT, C-FAF, C-FAH y C-HUM se obtuvo en el bosque. En SSDH, los contenidos de COT (0,0-0,05 m) y C-HUM (0,0-0,05 y 0,05-0,10 m) fueron más altos que aquellos encontrados bajo SPC. Los contenidos más altos de C-FAF se encontraron bajo SPC. En SSDH en comparación con SPC favorece el proceso de humificación (mayor contenido de C-HUM y menores índices de C-FAH + C-FAF/C- HUM (en las profundidades de 0.0-0.05 y 0,05-0,10 m) y la protección de la materia orgánica (mayor contenido de COT a 0,0-0,05 m de profundidad)). Entre las especies de plantas de cobertura, el centeno solo y centeno asociado con nabo tuvieron los mejores resultados en cuanto a la humificación de materia orgánica con predominio de C-HUM y C-FAH. Este patrón también se observó en el control para o C-HUM, debido a la abundancia de familias de plantas y especies, lo que indica que la biodiversidad de las plantas es una forma efectiva de mejorar la calidad del suelo.

ABSTRACT Nutrients present in soil aggregates are essential for maintaining the productive capacity of agroecosystems and environmental quality. The aim of this study was to evaluate the chemical properties of macroaggregates of a Humic Dystrudept cultivated with onions under a no-till vegetable system (NTVS) compared to the conventional tillage system (CTS) and a forest area in Ituporanga, SC, Brazil. The treatments consisted of the following single and mixed cover crops with onion under the NTVS: spontaneous vegetation, 100 % black oats, 100 % rye, 100 % oilseed radish, intercropped oilseed radish (14 %) + rye (86 %), and intercropped oilseed radish (14 %) + black oat (86 %). Additionally, we evaluated two areas, one with onion grown under the CTS for ±37 years and an area under forest for ±30 years, both adjacent to the experiment. Five years after implementation of the treatments with cover crops, we collected undisturbed soil samples at depths of 0.00-0.05, 0.05-0.10, and 0.10-0.20 m, and we obtained macroaggregates (8.00 mm > Ø ≥ 2.0 mm). We analyzed total organic carbon (TOC), pH in water, Ca2+, Mg2+, Al3+, H+Al, K+, and P in the macroaggregates. The conversion of onion-growing areas from the CTS to the NTVS after five years increases TOC, pH, Ca, Mg, and K in soil macroaggregates at the depth of 0.00-0.05 m. There is increased K content in the macroaggregates of soil under the NTVS at all depths evaluated in this study compared to the CTS. The use of millet in the CTS increases P content at depth (0.05-0.10 and 0.10-0.20 m). Intercropping black oat + oilseed radish increases Ca content at the 0.10-0.20 m depth in comparison to the black oat, rye + oilseed radish, and control treatments, and increases Mg content as well, compared to the other cover crops at the depths of 0.05-0.10 and 0.10-0.20 m.

Abstract High copper (Cu) levels in uprooted old vineyard soils may cause toxicity in transplanted young vines, although such toxicity may be reduced by inoculating plants with arbuscular mycorrhizal fungi (AMF). The objective of this study was to evaluate the effects of AMF on the plant growth, chlorophyll contents, mycorrhizal colonization, and Cu and phosphorus (P) absorption in young vines cultivated in a vineyard soil contaminated by Cu. Commercial vineyard soil with high Cu levels was placed in plastic tubes and transplanted with young vines, which were inoculated with six AMF species (Dentiscutata heterogama, Gigaspora gigantea, Acaulospora morrowiae, A. colombiana, Rhizophagus clarus, R. irregularis) and a control treatment on randomized blocks with 12 replicates. After 130 days, the mycorrhizal colonization, root and shoot dry matter (DM), height increment, P and Cu absorption, and chlorophyll contents were evaluated. The height increment, shoot DM and chlorophyll contents were not promoted by AMF, although the root DM was increased by R. clarus and R. irregularis, which had the greatest mycorrhizal colonization and P uptake. AMF increased Cu absorption but decreased its transport to shoots. Thus, AMF species, particularly R. clarus and R. irregularis, contribute to the establishment of young vines exposed to high Cu levels.