Dynamics of Carbon and Soil Enzyme Activities under Arabica Coffee Intercropped with Brachiaria decumbens in the Brazilian Cerrado.

The change in land use in the Brazilian Cerrado modifies the dynamics of soil organic matter (SOM) and, consequently, carbon (C) stocks and their fractions and soil enzyme activities. This study evaluated the effect of brachiaria (Brachiaria decumbens Stapf.) intercropped with Arabica coffee (Coffea arabica L.) on the stock and fractions of soil carbon and enzyme activities. The experiment was arranged in a completely randomized block design with three replications and treatments in a factorial design. The first factor consisted of coffee with or without intercropped brachiaria, the second of Arabica coffee cultivars ('I.P.R.103' and 'I.P.R.99') and the third factor of the point of soil sampling (under the canopy (UC) and in inter-rows (I)). Soil was sampled in layers of 0-10, 10-20, 20-30, 30-40, 40-60 and 60-80 cm. Soil from the 0-10 cm layer was also used to analyze enzymatic activity. Significant effects of coffee intercropped with brachiaria were confirmed for particulate organic carbon (POC), with highest contents in the 0-10 and 20-30 cm layers (9.62 and 6.48 g kg-1, respectively), and for soil enzymes (280.83 and 180.3 µg p-nitrophenol g-1 for arylsulfatase and ß-glucosidase, respectively).

Understanding the Relations between Soil Biochemical Properties and N2O Emissions in a Long-Term Integrated Crop-Livestock System.

Edaphoclimatic conditions influence nitrous oxide (N2O) emissions from agricultural systems where soil biochemical properties play a key role. This study addressed cumulative N2O emissions and their relations with soil biochemical properties in a long-term experiment (26 years) with integrated crop-livestock farming systems fertilized with two P and K rates. The farming systems consisted of continuous crops fertilized with half of the recommended P and K rates (CCF1), continuous crops at the recommended P and K rates (CCF2), an integrated crop-livestock system with half of the recommended P and K rates (ICLF1), and an integrated crop-livestock at the recommended P and K rates (ICLF2). The ICLF2 may have promoted the greatest entry of carbon into the soil and positively influenced the soil's biochemical properties. Total carbon (TC) was highest in ICLF2 in both growing seasons. The particulate and mineral-associated fractions in 2016 and 2017, respectively, and the microbial biomass fraction in the two growing seasons were also very high. Acid phosphatase and arylsulfatase in ICLF1 and ICLF2 were highest in 2016. The soil properties correlated with cumulative N2O emissions were TC, total nitrogen (TN), particulate nitrogen (PN), available nitrogen (AN), mineral-associated organic carbon (MAC), and microbial biomass carbon (MBC). The results indicated that ICLF2 induces an accumulation of more stable organic matter (OM) fractions that are unavailable to the microbiota in the short term and result in lower N2O emissions.

Soil Carbon Stocks and Greenhouse Gas Mitigation of Agriculture in the Brazilian Cerrado-A Review.

New agricultural practices and land-use intensification in the Cerrado biome have affected the soil carbon stocks. A major part of the native vegetation of the Brazilian Cerrado, a tropical savanna-like ecoregion, has been replaced by crops, which has caused changes in the soil carbon (C) stocks. To ensure the sustainability of this intensified agricultural production, actions have been taken to increase soil C stocks and mitigate greenhouse gas emissions. In the last two decades, new agricultural practices have been adopted in the Cerrado region, and their impact on C stocks needs to be better understood. This subject has been addressed in a systematic review of the existing data in the literature, consisting of 63 articles from the Scopus database. Our review showed that the replacement of Cerrado vegetation by crop species decreased the original soil C stocks (depth 0-30 cm) by 73%, with a peak loss of 61.14 Mg ha-1. However, when analyzing the 0-100 cm layer, 52.4% of the C stock data were higher under cultivated areas than in native Cerrado soils, with a peak gain of 93.6 Mg ha-1. The agricultural practices implemented in the Brazilian Cerrado make low-carbon agriculture in this biome possible.

Earthworm species in different land use systems in the state of Goiás and the Federal District of Brazil.

The state of Goiás and the Federal District together cover an area of about 346 thousand km2, including the diversified Cerrado vegetation, also known as the Brazilian Savanna, a biodiversity hotspot with many endangered and endemic species. Much of the Cerrado has been converted to agriculture, but little is known of its earthworms, and the impacts of land use management and agricultural practices on their density and diversity. In the present paper we review the known earthworm species in Goiás and the Federal District based on historical and museum records, and update information on their distribution and populations in different counties and land use systems with data from recent samplings. Five additional species are reported here for the first time, raising the total to 12 species currently known from Goiás, from the families Benhamiidae (1), Glossoscolecidae (1), Megascolecidae (3), Ocnerodrilidae (2) and Rhinodrilidae (5). In the Federal District, an additional 10 species are reported, bringing the total to 23 earthworm species, belonging to the families Benhamiidae (4), Eudrilidae (1), Glossoscolecidae (2), Ocnerodrilidae (1), Lumbricidae (2), Megascolecidae (1) and Rhinodrilidae (12). Native species in Goiás (6) were found in areas with lesser disturbance, such as in native forest and flooded areas/river banks, a phenomenon also observed in the Federal District. On the other hand, the exotic and peregrine species found in Goiás (6) and in the Federal District (9) dominated in disturbed sites, such as perennial crops, agroforestry, annual crops, urban areas, secondary forests, pastures and agropastoral systems, among others. Given the many new species found and the extension of Goiás and the Federal District, further effort is needed to adequately characterize the earthworm fauna of the region, from where many other species are expected.

Nitrogen Use Efficiency in an Agrisilviculture System with Gliricidia sepium in the Cerrado Region.

Gliricidia (Gliricidia sepium) is a tree legume that has great potential for use in agriculture because of its multiple-use characteristics. However, there is little information in the literature about the effect of agrisilvicultural systems on nitrogen (N) cycling. This study evaluated the effect of densities of gliricidia on N cycling under an agrisilvicultural system. The treatments were composed of different densities of gliricidia: 667, 1000 and 1333 plants ha-1, with a fixed spacing of 5 m between the alleys. The efficiency of N use was investigated by using the 15N isotope tracer. In each plot, a transect perpendicular to the tree rows was established in two positions: (i) in the corn (Zea mays) row adjacent to the trees, and (ii) in the corn row in the center of the alley. The N fertilizer recovery efficiency ranged from 39% in the density of 667 plants ha-1 to 89% with 1000 plants ha-1. The effect of gliricidia on the N uptake by corn was higher in the central position of the alley with 1000 plants ha-1. The agrisilvicultural system with 1000 plants ha-1 was highly efficient in the recovery of mineral N, representing an excellent option for integrated production systems in tropical regions.

Soil macrofauna associated with cover crops in an Oxisol from the southwest of Piauí state, Brazil / Macrofauna edáfica associada a plantas de cobertura em um Latossolo Amarelo do sudoeste do estado do Piauí, Brasil

The soil macrofauna is fundamental for the maintenance of soil quality. The aim of this study was to characterize the soil macrofauna under different species of cover crops, including monoculture or intercropping associated to two types of soil management in the southwest region of Piauí state. The study was carried out in an Oxisol (Latossolo Amarelo, according to Brazilian Soil Classification System) in the municipality of Bom Jesus, Piauí, distributed in 30 m2 plots. Testing and evaluation of the soil macrofauna were conducted in a 9 × 2 strip factorial design, with combinations between cover crops/consortia and soil management (with or without tillage), with four replications. Soil monoliths (0.25 × 0.25 m) were randomly sampled in each plot for macrofauna at 0‒0.1, 0.1‒0.2, and 0.2‒0.3 m depth, including surface litter. After identification and counting of soil organims, the relative density of each taxon in each depth was determined. The total abundance of soil macrofauna quantified under cover crops in the conventional and no-tillage system was 2,408 ind. m-2, distributed in 6 classes, 16 orders, and 31 families. The results of multivariate analysis show that grass species in sole cropping systems and no-tillage presents higher macrofauna density, in particular the taxonomic group Isoptera. No-tillage also provided higher richness of families, where Coleoptera adult were the second more abundant group in no-tillage and Hemiptera in conventional tillage.(AU)

Os organismos da macrofauna edáfica são fundamentais para a manutenção da qualidade do solo. O objetivo deste trabalho foi caracterizar a macrofauna edáfica sob diferentes espécies de plantas de cobertura, incluindo monocultura ou cultivo consorciado associados a dois tipos de manejo do solo no sudoeste do Piauí. O estudo foi realizado em Latossolo Amarelo (Sistema Brasileiro de Classificação de Solos) no município de Bom Jesus, Piauí, distribuídos em parcelas de 30 m2. O experimento e avaliação da macrofauna edáfica foram conduzidos em um ensaio fatorial em faixas 9 × 2, com combinações entre culturas /consórcios de cobertura e manejo do solo (com ou sem preparo), com quatro repetições. Os monólitos de solo (0,25 × 0,25 m) foram retirados aleatoriamente de cada parcela, para contagem da macrofauna, nas camadas de 0‒0,1, 0,1‒0,2, e 0,2-0,3 m de profundidade, inclusive liteira de superfície. Após a identificação e contagem dos organismos, foi determinada a densidade relativa de cada táxon em cada profundidade. A abundância total da macrofauna edáfica quantificada no experimento foi de 2.408 ind.m-2, distribuídos em 6 classes, 16 ordens e 31 famílias. Os resultados da análise multivariada revelaram que espécies de gramíneas em sistemas de cultivo solteiro e plantio direto favoreceram maior densidade da macrofauna, em especial do grupo taxonômico Isoptera. A ausência de preparo também proporcionou maior riqueza de famílias, destacando-se o grupo taxonômico Coleoptera adulto em plantio direto e Hemiptera em plantio convencional.(AU)

Evidence of limited carbon sequestration in soils under no-tillage systems in the Cerrado of Brazil.

The Brazilian government aims at augmenting the area cropped under no-tillage (NT) from 32 to 40 million ha by 2020 as a means to mitigate CO2 emissions. We estimated soil carbon (C) sequestration under continuous NT systems in two municipalities in the Goiás state that are representative of the Cerrado. A chronosequence of NT fields of different age since conversion from conventional tillage (CT) was sampled in 2003 and 2011. Soil C levels of native Cerrado and pasture were measured for comparison. After about 11 to 14 years, soil C stocks under NT were highest and at the levels of those under natural Cerrado. Average annual rates of soil C sequestration estimated using the chronosequence approach were respectively 1.61 and 1.48 Mg C ha(-1) yr(-1) for the 2003 and 2011 sampling, and were higher than those observed using repeated sampling after eight years. The diachronic sampling revealed that the younger NT fields tended to show higher increases in soil C stocks than the older fields. Converting an extra 8 million ha of cropland from CT to NT represents an estimated soil C storage of about 8 Tg C yr(-1) during 10 to 15 years.

Recuperação de carbono obtida por três métodos em frações da matéria orgânica de latossolo, sob consórcio milho-forrageiras, no cerrado / Carbon recovery obtained by three methods in organic matter fractions of latosol under maize-grass intercropping in the cerrado

A dinâmica da matéria orgânica do solo (MOS) pode ser melhor compreendida após identificadas suas frações lábeis (> 53 µm) e estáveis (< 53 µm). Diante da importância crescente do uso de técnicas de fracionamento físico da MOS, torna-se necessário avaliar se a recuperação de carbono nessas frações é influenciada pelos métodos utilizados para sua determinação. O objetivo deste trabalho foi avaliar os teores de carbono, por três métodos, em diferentes frações da matéria orgânica, num Latossolo Vermelho-Amarelo distrófico sob consórcio milho-forrageiras e em sistema solteiro. Foram determinados os teores de carbono das frações: (i) particulada da matéria orgânica (COP) e naquela (ii) associada aos minerais da matéria orgânica (COM). Determinou-se ainda, o teor de (iii) carbono orgânico total do solo (COT) na matéria orgânica não fracionada. Três métodos de determinação do carbono orgânico do solo foram utilizados: (i) Walkley & Black modificado, (ii) Mebius modificado, e (iii) combustão via seca, em analisador elementar (CHN). Foram utilizadas amostras de solos de três sistemas de manejo dispostos em delineamento em blocos casualizados, com três repetições para determinação do carbono orgânico do solo: (i) milho solteiro; (ii) milho consorciado com capim colonião (Panicum maximum cv. Aruana); e (iii) milho consorciado com braquiária (Brachiaria humidicola). As amostras de solo foram coletadas na profundidade de 0 ­ 5 cm. O método Walkley & Black apresentou menores valores de COT em relação ao CHN nos sistemas de manejo milho/braquiária e milho solteiro, e mostrou valores de COP semelhantes àqueles obtidos pelo CHN nos sistemas de manejo milho solteiro e milho/braquiária. Valores de COT, COP e COM obtidos pela metodologia de Mebius modificado foram semelhantes àqueles obtidos pelo analisador elementar, para todos os sitemas de manejo. O COP, quando avaliado pelas metodologias de Mebius e CHN, mostrou-se significativamente mais sensível às alterações de manejo em relação ao COT e COM.

Soil organic matter alterations can be better understood when it is fractionated for the identification of its labile (> 53 µm) and stable (< 53 µm) fractions. Because of the increasing and important use of soil organic matter fractionation techniques, it becomes necessary to evaluate if the carbon recovery in these fractions is influenced by methods used for its determination. The aim of this work was to evaluate the content of organic carbon in soil organic matter fractions, by three different methods, under maize-grass intercropping and sole maize in a dystrophic Red-Yellow Latosol (Oxisol). The following carbon contents were determined from the fractions: (i) of the particulate soil organic matter (POM) and from that (ii) of mineral-associated soil organic matter (MOC). The content of total organic carbon (TOC) was also determined in the non-fractionated soil organic matter. Three methods for the determination of soil organic carbon were used: (i) Walkley & Black modified, (ii) Mebius modified, and (iii) dry combustion in a CHN elemental analyzer. The experimental design was a randomized block design with three replications. Soil samples were collected from three management systems: (i) sole corn; (ii) maize-Panicum maximum intercropping; and (iii) maize- Brachiaria humidicola intercropping. Soil samples were collected from the depth of 0 ­ 5 cm. Lower TOC were found in the Walkley & Black method in relation to the CHN elemental analyzer, under the management systems sole maize and maize-Panicum maximum intercropping. However, the Walkley & Black method showed similar POM in relation to CHN analyzer method, under the management systems sole maize and maize-Brachiaria humidicola intercropping. TOC, POM and MOC obtained from the Mebius modified method were similar to those obtained from the elemental analyzer, under the three management systems. The POM when evaluated by the Mebius and CHN methods, showed to be more sensible to soil management alterations.