ABSTRACT An important strategy for the sustainable management of Cerrado soils is no-till (NT) systems, which may improve soil properties, particularly aggregation. Soil aggregates can be categorized according to their formation pathways into physicogenic (Phy) and biogenic (Bio). This study aimed (i) to quantify the relative proportion of physicogenic and biogenic aggregates and (ii) evaluate the levels of total organic carbon and their respective humic and physical fractions in the aggregates’ formation pathways. The following managed and unmanaged sites were evaluated: a 6-year no-till site (6NT), an 18-year no-till site (18NT), a conventional tillage site (CT), and a reference Cerrado site (RS). Retained aggregates were analyzed morphologically, separated into Phy and Bio, and quantified. Subsequently, aggregates were subjected to total organic carbon (TOC) determination, fulvic acid carbon, humic acid carbon, humin carbon, particulate organic carbon (POC), mineral-associated organic carbon, and free light fraction carbon (FLFC). The proportion of Bio aggregates increased with decreasing management intensity. When TOC and humic acid carbon levels were compared between sites, it was found that Bio aggregates from 18NT and 6NT contained higher carbon content than Bio aggregates from CT. Particulate organic carbon and FLFC differed between aggregate types, with higher POC values observed in Bio aggregates from CT and 18NT and higher FLFC values in Bio aggregates from CT, 6NT, and 18NT. The practices adopted in the conservation management system favored biogenic aggregation in the Cerrado region, which can be proven through the study of the fractions of soil organic matter contained in these aggregates. The biogenic aggregation changed the SOM dynamics. Principal component analysis showed a clear distinction between conventional and conservationist management systems.

ABSTRACT New strategies for sugarcane production have been very important since the incorporation of ethanol in the Brazilian energy mix in the early 1970s. Prior to planting sugarcane, the soil is prepared, and this process can affect root development and, consequently, sugarcane production. This study was conducted in an area of sugarcane crop renewal in the Cerrado biome (Brazilian tropical savanna), with the objective of identifying which tillage system generates the better root development and improved yield in sugarcane. The treatments were: 1) weed desiccation + moldboard plowing (0.4 m) + mild spike tooth harrowing (0.15 m); 2) subsoiler (0.3 m) + mild spike tooth harrowing (0.15 m); 3) weed desiccation + no-tillage (furrow opening and fertilizer); 4) weed desiccation + subsoiler (0.4 m); 5) ratoon destruction + subsoiler (0.4 m); 6) ratoon destruction + spike tooth harrowing (0.2 m) + moldboard plowing (0.4 m) + mild spike tooth harrowing (0.15 m). Characteristics of the sugarcane root system, such as the root length density, average distance between roots, and root soil exploration, after the first harvest (1.5 years) were studied. Root length density was greater for the treatments that included plowing (0.4 m) and harrowing (0.15 m) operations. The average distance between roots was low in the no-tillage system. The highest sugarcane yield in the plant crop was achieved by management practices with more extensive soil profile disturbances, like plowing followed by harrowing.

ABSTRACT We evaluated nutrient cycling by measuring leaf litter production and decomposition in the Brazilian savanna (cerrado sensu stricto) on eutrophic (calcareous) and dystrophic (arenitic) Neosols over the same spatiotemporal scale. We installed three transects in the Cerrado with plots in each Neosol type. Areas along the transects were randomly chosen for determining soil chemical properties, and accumulated leaf litter was collected monthly for a year for analysis. We used litter bags to test for a correlation between loss of dry mass and nutrient release. The calcareous cerrado had higher levels of macronutrients, higher pH, and lower Al compared to the arenitic cerrado. The estimated annual release of leaf litter nutrients in kg ha-1 yr-1 was higher in the calcareous cerrado. Nutrient concentration was significantly higher in different months in the calcareous cerrado, except for S and N. In general, the loss of dry mass was not correlated with nutrient release. Calcareous Neosol is unique to the cerrado sensu stricto, and retains more nutrients and facilitates higher leaf litter chemical quality than cerrado of the same physiognomy on dystrophic soils. Nutrient release is not always related to loss of dry mass, regardless of the amount of leaf litter.

ABSTRACT The sugarcane green harvest system, characterized by mechanized harvesting and the absence of crop burning, affects soil quality by increasing crop residue on the soil surface after harvest; thus, it contributes to improving the physical, chemical, and microbiological properties and influences the soil carbon content and CO2 flux (FCO2). This study aimed to evaluate the spatial and temporal variability of soil FCO2 in sugarcane green harvest systems. The experiment was conducted in two areas of sugarcane in São Paulo, Brazil: the first had a 5-year history of sugarcane green harvest (SG-5) and the second had a longer history of 10 years (SG-10). The temporal FCO2 were evaluated in the dry and rainy periods, and spatial variability in the dry period, and related to soil chemical and physical properties, including organic C porosity, bulk density, soil penetration resistance, mean weight diameter of soil aggregates, clay, P, S, Ca, Mg and Fe. The temporal variability indicated no differences between the dry and rainy periods in SG-10, while in SG-5 soil moisture was increased by 33 % in the rainy period. The spatial variability indicated a different pattern from the temporal one, where FCO2 in SG-10 was correlated with soil temperature, air-filled pore space, total porosity, soil moisture, and the Ca and Mg contents; in the SG-5 area, FCO2 was correlated with soil mean weight diameter of soil aggregates and the sulfur content.

RESUMOOs resíduos das plantas de cobertura e das culturas comerciais deixados sobre a superfície do solo podem influenciar a decomposição, ciclagem de nutrientes e a produtividade das culturas subsequentes. Neste estudo objetivouse avaliar a produção de fitomassa seca (FS), taxa de decomposição dos resíduos e o rendimento de milho e soja, cultivados sobre diferentes coberturas de solo. O delineamento utilizado foi de blocos casualizados no esquema em faixas, com quatro coberturas: braquiária, crotalária, milheto e pousio no período outono/inverno, com milho e soja em sucessão na primavera/verão. Avaliou-se FS, a decomposição através das sacolas de decomposição e o rendimento de milho e soja. Milheto e crotalária foram às coberturas que apresentaram maior produção de fitomassa seca no período outono/inverno; a produção de fitomassa seca de milho e soja não foi influenciada pelas coberturas de solo avaliadas; a taxa de decomposição dos resíduos vegetais de milho e soja é lenta no período seco e acelerada no chuvoso; o rendimento do milho foi superior quando cultivado sobre crotalária e braquiária nos anos avaliados, enquanto que para soja não ocorreram diferenças sobre qualquer cobertura avaliada; Milho e soja apresentam rendimentos de grãos superiores à média regional quando cultivados sobre as diferentes coberturas do solo.

ABSTRACTThe residues of cover plants and crops left on the soil surface can influence decomposition, nutrient cycling and follow crop yield. The objective was to evaluate the production of dry biomass (BD), of residues decomposition rate and yield of maize and soybean grown on different soil covers. The experimental design was a randomized block scheme banded, with four covers: Brachiaria, sun hemp, pearl millet and fallow period in autumn/winter, with maize and soybean crop in the spring/summer. We evaluated BD, decomposition through bags of decomposition and yield of maize and soybeans. Pearl millet and sunhemp were the covers which produced more of BD in the fall/winter period. the rate of decomposition of plant residues in maize and soybeans is slow in the dry period and accelerated in the rainy period; maize yield was higher when grown on sunhemp and brachiaria in the years evaluated, while for soybeans there were no differences on any measured coverage; maize and soybeans have grain yields higher than the regional average when grown on different soil covers.

A utilização do sistema de semeadura direta associado ao uso de plantas de cobertura e à rotação de culturas altera alguns atributos físicos do solo e pode indicar mudança em sua qualidade. Este estudo objetivou utilizar o índice de estabilidade de agregados (IEA) e o índice de sensibilidade (IS) para avaliar alterações nos atributos físicos do solo com o uso de diferentes plantas de cobertura após 12 anos de semeadura direta. Com delineamento de blocos ao acaso, utilizaram-se as coberturas: crotalária, milheto, sorgo, braquiária, pousio (vegetação espontânea), amostradas no ano de 2012, mais uma testemunha sem cobertura (semeadura convencional) desde o ano de 2000, em que foram coletadas três amostras por parcela, perfazendo um total de 12 amostras por tratamento, com quatro repetições. Foram avaliadas a densidade do solo (Ds), macroporosidade (Ma), microporosidade (Mi), porosidade total (PT), estabilidade dos agregados (EA), diâmetro médio geométrico (DMG) e ponderado (DMP), índice de sensibilidade (Is) e índice da porcentagem de agregados com diâmetro superior a 2 mm (AGRI). A utilização das diferentes coberturas e a introdução do sistema de semeadura direta após 12 anos causaram alterações positivas nos atributos físicos na camada superficial do solo. As correlações positivas e negativas significativas entre densidade do solo e os outros atributos físicos avaliados evidenciaram a sua importância como bom indicador da qualidade do solo. Por meio do índice de sensibilidade, constatou-se que microporosidade aumentou mais do que os outros atributos físicos após a implantação do sistema de semeadura direta na área.

The use of no-tillage systems associated with the use of cover crops and crop rotation changes some soil physical properties and may indicate change in soil quality. This study aimed to use the aggregate stability index (IEA) and the sensitivity index (SI) to assess changes in soil physical attributes with the use of different plant cover after twelve years of no-tillage. We used a randomized block design with the following types of cover crops: sunn hemp, millet, sorghum, brachiaria, and fallow (natural vegetation) sampled in 2012, and a control (conventional planting) since 2000, in which three samples were collected per plot for a total of 12 samples per treatment, with four replications. We evaluated soil bulk density (Bd), macroporosity (Ma), microporosity (Mi), total pore volume (TPV), aggregate stability (AS), geometric mean diameter (GMD), mean weighted diameter (MWD), sensitivity index (SI), and index of the percentage of aggregates with diameter greater than 2 mm (AGRI). The use of different crop covers and the introduction of the no-tillage seeding system after twelve years caused positive changes in the physical properties of the soil surface layer. The positive and negative correlations between and significant soil density and the other evaluated physical attributes showed its importance as an indicator of soil quality. Through the sensitivity index, it was observed that microporosity increased more than the other physical attributes after the implementation of the no-tillage system in the area.

A irrigação por aspersão em pastagem pode aumentar a produção de forragem e melhorar as condições químicas do solo. O objetivo deste trabalho foi avaliar a fertilidade e os teores de carbono total e oxidável de Latossolo Vermelho Distrófico de Cerrado em área de pastagem Tifton 85 (Cynodon spp), irrigada e sequeiro. O delineamento experimental foi inteiramente casualizado. Amostras de solo nas camadas de 0-5, 5-10, 10-20 e 20-40cm foram coletadas para avaliação dos teores de Ca, Mg, Al, P, K, Na, H+Al, carbono orgânico total (COT) e determinação de pH. As amostras foram fracionadas quimicamente com dicromato de potássio para a obtenção de frações com diferentes graus de labilidade: F1>F2>F3>F4. A área irrigada apresentou maiores teores de Ca e Mg em relação à área de sequeiro, exceto para o Mg, na profundidade 10-20cm. Foi observada diferença para os teores de COT, sendo os maiores valores verificados na área irrigada, decorrente do maior aporte de biomassa aérea e radicular. Esse padrão também foi constatado para as frações F1 e F2. A irrigação aumenta a concentração de COT, sendo esse aumento mais perceptível nas frações mais lábeis (F1 e F2), e também proporciona a melhoria da fertilidade do solo, aumentando os teores de Ca e Mg.

The sprinkler irrigation on pasture can increase the forage production and improve soil chemical conditions. The aim of this study was to evaluate soil fertility and oxidizable and total carbon contents in Oxisol of the Cerrado under pasture area Tifton 85 (Cynodon spp), irrigated and dryland. The experimental design was completely randomized. Soil samples were collected in the 0-5, 5-10, 10-20 and 20-40cm depth, to evalueted the tenors of Ca, Mg, Al, P, K, Na, H + Al, total organic carbon (TOC) and determined the pH values. The samples were chemically fractionated with potassium dichromate to obtain fractions with different degrees of lability: F1>F2>F3>F4. The irrigated area had the highest Ca and Mg tenors in relation to the no-irrigated area, except for Mg, 10-20cm depth. It was observed difference for the TOC, and the highest values were verified in the irrigated area, due to higher contribution of stem and root biomass at all depths. This pattern was also observed for fractions F1 and F2. The irrigation increases the concentration of TOC, being this increase most noticeable in the more labile fractions (F1 and F2) and also provides improved soil fertility by increasing the concentration of Ca and Mg.

A produção de biomassa, a manutenção dos resíduos vegetais sobre o solo e sua posterior decomposição são fatores de grande importância no estudo da ciclagem de nutrientes. Este estudo foi desenvolvido na área experimental do CEFET-Uberaba-MG, onde foram avaliados oito tipos de coberturas vegetais: milheto (Pennisetum americanum sin. tiphoydes), braquiária (Brachiaria brizantha), sorgo-forrageiro (Sorghum bicolor L. Moench), guandu (Cajanus cajan (L.) Mill sp.), crotalária (Crotalarea juncea), aveia-preta (Avena strigosa Schreb), pousio e área em preparo convencional de solo (testemunha) em área de Cerrado, na região do Triângulo Mineiro. Avaliaram-se a fitomassa seca (FS), a decomposição dos resíduos em bolsas de decomposição, e a liberação de K. Utilizou-se um modelo matemático para descrever a decomposição dos resíduos e a liberação de K, e calcularam-se a constante de decomposição (k) e o tempo de meia-vida (T½). O milheto, o sorgo e a crotalária foram as coberturas que apresentaram maiores produções de matéria seca. O maior acúmulo de K ocorreu em gramíneas e a maior liberação de K ocorreu no milheto, aveia, braquiária e crotalária nos primeiros 42 dias após manejo, nos dois períodos avaliados. A braquiária apresentou o menor T½ vida e a maior taxa de liberação de K.

Crop residue production, plant residue maintenance and their decomposition are important factors in the understanding of nutrient recycling process. To evaluate K accumulation and release a study with eight cover crops types was developed: pearl millet (Pennisetum americanum sin. tiphoydes), brachiaria grass (Brachiaria brizantha), sorghum (Sorghum bicolor L. Moench), pigeonpea (Cajanus cajan (L.) Millsp), sunn hemp (Crotalarea juncea) and black oats (Avena strigosa Schreb), fallow land and conventional culture (control) in the experimental area of CEFET-Uberaba-MG, in a Cerrado area. The dry mass production, crop residue decomposition in litter bags and K release were evaluated. A mathematical model was used to describe residue decomposition and K release, which calculates the decomposition constant (k) and half-time life. Pearl millet, sorghum and the sunn hemp were the cover crops that produced most dry matter while K accumulation was highest in the grasses. K release was highest in pearl millet, oats, brachiaria grass and sunn hemp in the first 42 days after handling. Brachiaria grass had the shortest half-time life and the highest K release rate.

Com objetivo de diagnosticar a deterioração socioeconômica, ambiental e avaliar as características morfométricas da microbacia do Córrego Alegria, visitou-se a área de estudo, aplicando-se questionários numa amostra da população local. A deterioração social (S) é de 46 %, considerado médio, pois o nível de escolaridade, alimentação e as condições de trabalho são bons na região. Para o fator econômico (E) obteve-se 48 %, valor elevado, pois as propriedades são de média a alta produtividade, com renda média variando de 5 a 15 salários mínimos, além de contar com assistência técnica e ser cooperados. Para o fator tecnológico (T) obteve-se 32 %, valor baixo, devido ao tipo de exploração local. Para o fator sócio-econômico (S+E+T) obteve-se 44 %, considerado alto, que deveria limitar as condições de vida do produtor, porém isto não é observado. A deterioração ambiental calculada é de 15%, abaixo do esperado, sendo este valor justificado pela constante fiscalização e investimentos na recuperação da área, principalmente após o acidente ferroviário ocorrido em junho de 2003. A microbacia tem uma forma mais alongada, sendo comprovado pelo Ic de 060, Kc de 0,98 e Kf de 0,15, além da Dd de 1,10 km/km² e a declividade da bacia de 1,20%. Estes valores associados mostram uma área sem problemas de enchentes e erosões ao longo do Córrego. Os índices obtidos ainda não demonstram uma deterioração ambiental elevada.

With objective of to diagnose the deterioration socioeconomic, environmental and to evaluate the morphometric characteristics of the microbasin of the Stream Happiness's, the study area was visited, applying itself questionnaires in a sample of the local population. The social deterioration (S) it is of 46%, considered medium, because the education level, feeding and the work conditions are good in the region. For the economical factor (E) it was obtained 48%, high value, because the properties are of average the high productivity, with medium income varying from 5 to 15 minimum wages, besides counting with technical support and to be cooperated. For the technological factor (T) it was obtained 32%, low value, due to the type of local exploration. For the socioeconomic factor (S+E+T) it was obtained 44%, considered loud, that it should limit the conditions of life of the producer, however this is not observed. The calculated environmental deterioration is of 15%, below the expected, being this justified value for the constant fiscalization and investments in the recovery of the area, mainly after the rail accident happened in June of 2003. The microbasin has a more prolonged form, being proven for Ic 060, Kc 0,98 and Kf of 0,15, besides Dd of 1,10 km/km² and the declivity of the 1,20% basin. These associated values show an area without problems of inundations and erosions along the Stream. The indexes obtained don't still demonstrate a high environmental deterioration.

A produção de massa seca, a taxa de decomposição e a liberação de nitrogênio (N) foram avaliadas em um experimento com sete tipos de cobertura vegetal: milheto pérola (Pennisetum americanum sin. tiphoydes), braquiária (Brachiaria brizantha), sorgo forrageiro (Sorghum bicolor L. Moench), guandu (Cajanus cajan (L.) Millsp), crotalária juncea (Crotalarea juncea) e aveia-preta (Avena strigosa Schreb), em pousio e em área de cultivo convencional (testemunha), em solo de cerrado, em Uberaba, região do Triângulo Mineiro. Dentre as coberturas avaliadas, o milheto e a crotalária foram as que apresentaram a maior produção de massa seca, maior acúmulo e a maior liberação de N. A braquiária foi a cobertura que apresentou a maior taxa de decomposição. Todas as coberturas apresentaram a maior taxa de liberação de N até 42 dias após dessecação.

Dry mass production, decomposition rate and nitrogen (N) release were evaluated in a field experiment under seven cover crop types: pearl millet (Pennisetum americanum sin. typhoides), brachiaria grass (Brachiaria brizantha), sorghum (Sorghum bicolor L. Moench), pigeon pea (Cajanus cajan (L.) Mill sp), sunn hemp (Crotalaria juncea) and black oat (Avena strigosa Schreb), compared to a fallow and a traditional cropping system (control) in a cerrado soil (Uberaba-MG, Brazil). Among the tested cover crops, pearl millet and sunn hemp presented higher dry mass yield and nitrogen accumulation and release. Brachiaria grass had the highest decomposition rate and shortest half-life time. All crops reached the highest N liberation rate 42 days after desiccation.