Abstract The no-tillage system associated with crops rotation affects the dynamics of soil organic matter, influencing the formation, reorganization and stabilization of aggregates and the carbon content (C) into soil aggregates. The aim of this study was to evaluate the effect of crop rotations under no-tillage system on C content and soil aggregation. The experiment was conducted at the Paraná Agronomic Institute in Ponta Grossa, PR, Brazil. The treatments consisted of six crop rotations, in a 3-year cycle, arranged in a randomized block design with four replications. Soil samples were collected at layers of 0-5, 5-10 and 10-20 cm. The aggregate classification was determined by the wet sieving methodology, and the Weighted Mean Diameter (WMD), Geometric Mean Diameter (GMD) and Aggregate Stability Index (ASI) were calculated. The C content in the aggregates was determined by wet oxidation. The results were submitted to analysis of variance and Tukey test at 5% probability. There was no difference among crop rotations for aggregate classes and aggregation indexes, but were higher in surface, decreasing in depth. The carbon content in the aggregates did not differ among crop rotations, but presented stratification in the soil profile, decreasing in depth. The cycle of three years with crop rotation was insufficient to express possible changes in soil C content and aggregation.

Abstract The effectiveness soil cover in no-till is relating to quantity and quality of the phytomass produced by crops in rotation and, its persistence over the soil depends on residues decomposition. The objective of this study was to evaluate the phytomass production, decomposition rate and the half-life of crops in rotation at the Subtropical region, Brazil. The study was carried out at the Agronomic Institute of the Paraná (IAPAR), in Ponta Grossa, Parana State, Brazil. The experimental design was randomized blocks, with six treatments and four replicates. Winter cash crops and cover crops, single and in consortium, were evaluated in the year 2014 (wheat, black oats + hairy vetch + rye, black oats + ryegrass and black oats + blue lupine), in 2015 (canola, black oats, and black oats + hairy vetch + forage turnip) and in 2016 (barley, triticale, and triticale + black oats + rye). The phytomass was evaluating by collect three subsamples of 0.25 m2 per plot. For decomposition rate and the half-life of the crop residues, litter bags (LBs) methodology was used. A mathematical model (Q=Q0exp-kt) was used to represent the crop residues decomposition and the half-life of crop residues were obtained by the equation t1/2 = (ln2)/k. Poaceae consortia, single Poaceae and canola presented higher phytomass production when compared to Poaceae-Fabaceae consortia. The half-life for Poaceae-Fabaceae corsortia was shorter than single Poaceae.

Abstract The soil tillage practiced over a long period of time impacts soil quality. The first step in soil quality assessment is to select which indicators should be used. The objective of this study was to identify the soil attributes that discriminate soil tillage systems and can be used as indicators for soil quality assessments. Sixteen soil physical and chemical attributes were evaluated: macroporosity (MaP), microporosity (MiP), total porosity (TP), bulk density (BD), field-saturated hydraulic conductivity (Kfs), soil resistance to penetration (SRP), pH (H2O), pH (CaCl2), aluminium (Al), calcium (Ca), magnesium (Mg), potassium (K), available phosphorus (P), total organic carbon (TOC), cation exchange capacity (CEC) and base saturation (BS), of a very clayey Red Latosol, cultivated for a long period in no-till (NT), conventional tillage (CT) and minimum tillage (MT). The soil attributes (indicators) were selected using canonical discriminant analysis. MiP, Kfs, pH (CaCl2), Ca, Mg, CEC e BS were the most efficient indicators to discriminate soil tillage systems. In the indicator interpretation step was sustained MiP as the indicator that represents the function of physical stability and support, Kfs as the indicator that represents the function of water relations, BS as the indicator that represents the function of nutrient cycling and pH (CaCl2) as the indicator that represents the function of filtering and buffering. These indicators can be used for future soil quality assessment and monitoring of tillage systems in similar regions and conditions.

A adoção do sistema plantio direto e a manutenção dos resíduos culturais na superfície do solo resultam, com o passar dos anos, em adição de carbono (C) ao sistema, o que promove o sequestro de C e a mitigação de emissões de C-CO2 para a atmosfera. O objetivo deste trabalho foi avaliar a taxa de sequestro de C e a quantidade mínima de resíduos culturais necessária para manter o equilíbrio dinâmico (dC/dt = 0) de dois solos (Latossolo) com classes texturais diferentes. O delineamento experimental utilizado foi blocos ao acaso em arranjo fatorial 2 x 2 x 2. Os fatores analisados foram: (a) dois solos: Latossolo Vermelho distrófico típico, com classe textural franco-argiloarenosa (LVTM), e Latossolo Vermelho distrófico típico, com classe textural franco-argilosa (LVTA); (b) profundidades de amostragem: 0-0,05 e 0,05-0,20 m; e (c) épocas de amostragem (E1-outubro de 2007; E2-setembro de 2008). As lavouras onde foram coletadas as amostras vinham sendo manejadas em SPD por longo prazo (20 anos), com as seguintes rotações de cultura: trigo/soja/aveia-preta + ervilhaca/milho (LVTM) e trigo/milho/aveia-preta + ervilhaca/soja (LVTA). A taxa de sequestro anual de C foi de 0,83 e 0,76 Mg ha-1 para o LVTM e LVTA, respectivamente. A estimativa da quantidade mínima de resíduos culturais necessária para manter o equilíbrio dinâmico (dC/dt = 0) foi de 7,13 e 6,53 Mg ha-1 ano-1 para o LVTM e LVTA, respectivamente. A taxa de conversão de C em ambos os solos foi inferior à encontrada em outros estudos regionais, resultando numa elevada taxa de remanescente de palha na superfície do solo.

The adoption of no-tillage systems (NT) and the maintenance of crop residues on the soil surface result in the long-term increase of carbon (C) in the system, promoting C sequestration and reducing C-CO2 emissions to the atmosphere. The purpose of this study was to evaluate the C sequestration rate and the minimum amount of crop residues required to maintain the dynamic C equilibrium (dC/dt = 0) of two soils (Typic Hapludox) with different textural classes. The experiment was arranged in a 2 x 2 x 2 randomized block factorial design. The following factors were analyzed: (a) two soil types: Typic Hapludox (Oxisol) with medium texture (LVTM) and Oxisol with clay texture (LVTA), (b) two sampling layers (0-5 and 5-20 cm), and (c) two sampling periods (P1 - October 2007; P2 - September 2008). Samples were collected from fields under a long-term (20 years) NT system with the following crop rotations: wheat/soybean/black oat + vetch/maize (LVTM) and wheat/maize/black oat + vetch/soybean (LVTA). The annual C sequestration rates were 0.83 and 0.76 Mg ha-1 for LVTM and LVTA, respectively. The estimates of the minimum amount of crop residues required to maintain a dynamic equilibrium (dC/dt = 0) were 7.13 and 6.53 Mg ha-1 year-1 for LVTM and LVTA, respectively. The C conversion rate in both studied soils was lower than that reported in other studies in the region, resulting in a greater amount of crop residues left on the soil surface.

A redução no conteúdo de carbono (C) nas camadas mais profundas do solo indica a estratificação entre a camada superficial e as subsuperficiais, devido à adição contínua de C pelos resíduos culturais na superfície. O objetivo deste trabalho foi avaliar a variação (∆) da relação de estratificação (RE) de carbono como indicadora do sequestro de C total e particulado em macroagregados de dois Latossolos de classes texturais diferentes, manejados em sistema plantio direto. Os ensaios foram desenvolvidos em delineamento inteiramente casualizado com doze repetições. Os fatores analisados foram: (a) dois solos (Latossolo Vermelho Distrófico típico com classe textural franco-argilo-arenosa e Latossolo Vermelho Distrófico típico com classe textural franco-argilosa); (b) duas camadas de amostragem (0-5 e 5-20cm de profundidade); (c) duas épocas de amostragem (E1-outubro de 2007; E2-setembro de 2008). Observou-se relação linear e significativa entre o delta RE com a taxa de sequestro de C total em macroagregados no Latossolo Vermelho com classe textural franco argilo arenosa (R²=0,78**) e franco argilosa (R²=0,81**), indicando ter havido sequestro de C e confirmando ser este um indicador sensível da taxa de sequestro de C no solo em macroagregados.

The decrease in soil organic carbon (SOC) content in deeper layers indicates the occurrence of stratification between the surface layer and subsurface layer of soil due to continuous C addition by crop residues. The objective was to evaluate the change (delta) of stratification (RE) of carbon (C) as an indicator of C sequestration and soil total and particulate soil in macroaggregates of two soils (Typic Hapludox) with different textures, managed in no-tillage system. The tests were developed in completely randomized design twelve repetitions.Analyzed factors were: (a) two soils: Oxisol with medium texture and Oxisol with clay texture, (b) sampling depth: 0-5 and 5-20cm, (c) two sampling times (October 2007-T1, September 2008-T2). The results were submitted to variance analysis by program SISVAR 5.3, using the Tukey test at 5% significance. There was a significant linear relationship between the ∆ RE and carbon sequestration rate total macroaggregates Oxisol with medium texture (R²=0.78**) and Oxisol with clay texture (R²=0.81**) indicating that there was C sequestration confirming to be a sensitive indicator of the rate of C sequestration in soil macroaggregates.

Nos sistemas agrícolas o conteúdo de N-NH4+ e N-NO3- é significativamente afetado pelo manejo do solo. Estudou-se a dinâmica do nitrogênio (N) inorgânico (NH4+ e NO3-) em experimento com avaliação de sistemas de manejo do solo (SMS) implantado em 1988, na Estação Experimental da Fundação ABC, em Ponta Grossa, região Centro-Sul do Estado do Paraná. Objetivou-se, com este trabalho, avaliar as alterações ocasionadas pelos SMS no fluxo do N-NH4+ e N-NO3- na camada superficial de um Latossolo Vermelho, em um período de 12 meses. O delineamento experimental utilizado foi o de blocos completos ao acaso, em esquema de parcelas subdivididas com três repetições. As parcelas foram constituídas pelos seguintes SMS: 1) preparo convencional (PC); 2) preparo mínimo (PM); 3) plantio direto com escarificação a cada três anos (PDE); e 4) plantio direto permanente (PDP). Para avaliar a dinâmica do N inorgânico, as subparcelas foram constituídas pelo tempo de coleta (11 tempos de coleta - T1 a T11). O conteúdo de N amoniacal (N-NH4+) e de N nítrico (N-NO3-) foi superior nos sistemas com menor mobilização do solo (PM e PDE) e sem mobilização (PDP), em comparação com o PC. No período de outubro de 2003 a fevereiro de 2004, o conteúdo de N-NH4+ no solo foi superior ao de N-NO3-. Entretanto, no período de maio de 2004 a julho 2004 o conteúdo de N-NO3- foi superior. A maior flutuação do conteúdo do N-NH4+ e do N-NO3- ocorreu na camada de 0-2,5 cm, e o maior pico na concentração N-NH4+ e do N-NO3- aconteceu depois da aplicação de N em cobertura da cultura do trigo. Tanto o N-NH4+ quanto o N-NO3- apresentaram elevada correlação com o conteúdo de C-orgânico do solo, indicando que tais atributos variam juntos no sistema.

In agricultural systems the N-NH4+ and N-NO3- contents is significantly affected by soil management. This study investigated the dynamics of inorganic nitrogen (N; NH4+ and NO3-) in an experimental evaluation of soil management systems (SMSs) adopted in 1988 at the experimental station of the ABC Foundation in Ponta Grossa, in the Central South region of the State of Paraná. The objective of this study was to evaluate the changes in N-NH4+ and N-NO3- flux in the surface layer of a Red Latosol arising from SMSs over a 12-month period. The experiment was arranged in a completely randomized block design in split plots, in three replications. The plots consisted of the following SMSs: 1) conventional tillage (CT); 2) minimum tillage (MT); 3) no-tillage with chisel plow every three years (NT CH); and 4) continuous no-tillage (CNT). To evaluate the dynamics of inorganic N, the subplots represented samplings (11 sampling times, T1 - T11). The ammonium N (N-NH4+) and nitric N (N-NO3-) contents were higher in systems with reduced tillage (MT and NT CH) and without tillage (CNT) than in the CT system. In the period from October 2003 to February 2004, the N-NH4+ was higher than the N-NO3- soil content. Conversely, in the period from May 2004 to July 2004, the N-NO3- was higher than the N-NH4+ content. The greatest fluctuation in the N-NH4+ and N-NO3- contents occurred in the 0-2.5 cm layer, and the highest peak in the N-NH4+ and N-NO3- concentrations occurred after the surface application of N. Both N-NH4+ and N-NO3- were strongly correlated with the soil organic C content, which indicated that these properties vary together in the system.

O nitrogênio é o principal fator limitante na produtividade das culturas e sistemas de manejo do solo podem alterar as taxas de mineralização e de nitrificação. Em experimento sobre sistemas de manejo do solo implantado em 1988, na Estação Experimental da Fundação ABC, de Ponta Grossa, região Centro-Sul do Estado do Paraná, foi realizado um estudo sobre a dinâmica do nitrogênio inorgânico, visando contribuir para a estratégia de manejo dos solos que conduzam à sustentabilidade ambiental. O objetivo deste trabalho foi calcular as taxas líquidas de mineralização e nitrificação do N no solo e a correlação com o pH do solo, afetados por sistemas de manejo. O delineamento experimental utilizado foi o de blocos completos ao acaso, em esquema de parcelas subdivididas com três repetições. As parcelas foram constituídas pelos seguintes SMS: 1) preparo convencional (PC); 2) preparo mínimo (PM); 3) plantio direto com escarificação a cada três anos (PDE); e 4) plantio direto permanente (PDP). Para avaliar a dinâmica do N inorgânico, as subparcelas foram constituídas pelo tempo de coleta (11 tempos de coleta - T1 a T11). Nos sistemas PDP e PDE, as taxas líquidas de mineralização foram superiores às de PM e PC, na camada de 0-2,5 cm do solo, enquanto na camada de 2,5-5 cm a taxa de nitrificação foi maior. Logo após o manejo da aveia branca, as taxas de mineralização e nitrificação, em todas as camadas do solo, foram maiores no PM e no PC. No período de desenvolvimento da cultura da soja, nas camadas de 0-2,5 e 2,5-5 cm do solo as taxas de mineralização e nitrificação foram superiores nos sistemas PDP e PDE.

Nitrogen is the main limiting factor in crop productivity and thereby soil management systems may change the mineralization and nitrification rates. In an experiment on soil management systems implemented in 1988 at the experimental station Fundação ABC, Ponta Grossa, in the central South region of the State of Paraná, inorganic N dynamics were examined to find a soil management strategy with a view to a sustainable environment. The objective of this study was to calculate the net mineralization and nitrification rates of soil N and the correlation with soil pH under management systems. Randomized complete block design was used, in split plots, in three replications. The following soil management systems (SMSs) were adopted in the plots: 1) conventional tillage (CT); 2) minimum tillage (MT); 3) no-tillage with chisel plow every three years (NT CH); and 4) continuous no-tillage (CNT). To evaluate the dynamics of inorganic N, samples were collected from sub-plots at different times (11 sampling times - T1 to T11). In the CNT and NT CH, the net mineralization rates were higher in the MT and CT systems in the 0-2.5 cm soil layer, while the nitrification rate was higher in the 2.5-5 cm layer. Soon after implementing the white oat management, the mineralization and nitrification rates in all soil layers were higher in the MT and CT systems. In the period of soybean development, in the 0-2.5 and 2.5-5 cm soil layers, the mineralization and nitrification rates were higher in the CNT and NT CH than in the MT and CT systems.