Spatial variability of chemical indicators of Amazon agricultural soils through geomultivariate statistics, Brazil.

This work focuses on evaluating the spatial variability of chemical attributes of soils under different agricultural use and native forest, indicating which are the possible indicator attributes of changes in environmental, through the use and management of the soil. The study was carried out in the southern region of the Amazonas state, in an Argissolo Vermelho-Amarelo (Ultisol). Sampling grids were established measuring: 90 m × 70 m with regular soil collection spacing of 10 m for the guarana and forest areas; 90 m × 56 m spaced at 10 m × 8 m for annatto area; and 54 m × 42 m with spacing between points of 6 m for the cupuaçu area, totaling 80 sampling points in each area, with soil samples collected at depths of 0.0-0.05; 0.05-0.10 m and 0.10-0.20 m. The following attributes were determined: pH, Al3+, K+, Ca2+, Mg2+, P, H + Al, CEC, V% and m%. Descriptive, geostatistical and multivariate statistical analyzes were performed. The results show that it is possible to state that the descriptive, geostatistical and multivariate statistical techniques were able to identify the difference between the spatial variability of the attributes according to each specific use of individual soils. The multivariate analysis made it possible to select the attributes that most contribute to the variability of these soils, and with that, it was found that the forest showed less spatial variability in the surface layer, with higher reach values by scaled semivariograms.

Soil chemical attributes in areas under conversion from forest to pasture in southern Brazilian Amazon.

The south of the Brazilian Amazon is one of the largest cattle-producing regions in Brazil, however, most of the pastures are in low fertility soils. Thus, cattle breeders compensate for the low production of pastures, increasing the size of the areas, generating more deforestation and burning. These practices increase the chemical degradation process of Amazonian soils, making them increasingly infertile when improperly managed. With this, the objective of the work was to evaluate the impacts caused in the chemical attributes of soils, in areas under forest-to-pasture conversion, in the south of the Brazilian Amazon. The study was carried out in the district of União Bandeirantes, in an area of forest and two areas with pastures (brachiaria and mombaça grass). In the field, soil samples were collected at two depths (0.00-0.10 and 0.10-0.20 m), to carry out chemical analyzes. Further, uni, bi and multivariate statistical analyzes were carried out, besides geostatistical analyzes were carried out to study spatial variability and management zones. The conversion of forest to pasture increased the pH and exchangeable bases levels, reducing the availability of exchangeable aluminum and potential acidity, however, it induces losses of phosphorus and organic carbon from the soil. Among the pasture environments, the mombaça grass area presented higher fertility. Greater spatial variability of chemical attributes was observed in the environment with mombaça grass, indicating greater heterogeneity in the distribution of attributes in the area. We attribute this behavior to the higher grazing intensity and the micro-reliefs in the area that direct the flow of water and nutrients.

The stability of aggregates and organic carbon content after the application of gypsum, soil scarification and a succession of agricultural crops / A estabilidade dos agregados e do teor de carbono orgânico após a aplicação de gesso, escarificação do solo e uma sucessão de culturas agrícolas

Studies related to the monitoring of soil quality by physical attributes are important for the evaluation and maintenance of the sustainability of agricultural systems, besides indicating the appropriate management of the environment, aiming at its conservation and productivity. The objective of this study was to evaluate the stability of aggregates and organic carbon after the application of gypsum, soil scarification and a succession of crops. The treatments consisted of an absence and addition of gypsum, absence and presence of soil scarification, and three systems of crops in succession. The experimental design was made of randomized blocks, in a 2x2x4 factorial scheme, with eight replications. The aggregates were evaluated as stabled in water and soil organic carbon content. The treatment where gypsum was applied, as well as the soybean/maize/brachiaria/fallow (SMBF) succession system, presented better results in soil aggregation and higher levels of organic carbon.

Estudos relativos ao monitoramento da qualidade do solo pelos atributos físicos são importantes para a avaliação e manutenção da sustentabilidade dos sistemas agrícolas, além de sinalizar o manejo adequado do ambiente, visando à sua conservação e produtividade. Este trabalho teve por objetivo avaliar a estabilidade de agregados e teor de carbono orgânico, após a aplicação de gesso, escarificação do solo e sucessão de culturas. Os tratamentos consistiram na ausência e adição de gesso agrícola, ausência e presença de escarificação do solo, e três sistemas de sucessão de culturas. O delineamento experimental foi em blocos casualizados, em esquema fatorial 2x2x3 com oito repetições. Sendo avaliada a estabilidade dos agregados estáveis em água e teor de carbono orgânico do solo. O tratamento onde foi aplicado gesso agrícola e o sistema de sucessão SMBP apresentaram melhores resultados na agregação do solo e maiores teores de carbono orgânico.

Variability and spatial correlation of aggregates and organic carbon in indian dark earth in Apuí region, AM / Variabilidade e correlação espacial de agregados e carbono orgânico em terra preta de índio na região do Apuí, AM

Having in mind the importance of knowing the variability and spatial correlation of soil properties in Indian Dark Earth (IDE), we evaluated in this study the variability and the spatial correlation of aggregates and carbon in an Ultisol under coffee cultivation in southern Amazonas. It was established a 48 x 88 m sampling grid spaced 06 x 08 m, totalling 88 sampling points. Then soil samples were collected at: 0.0-.05, 0.05-0.10, and 0.10-0.20 m layers. The spatial variability of the Mean Weighted Diameter (MWD) attributes, aggregates > 2 mm, < 2 mm, bulk density (BD) and organic carbon (OC) was analyzed by adjusting the simple semivariograms, while spatial correlations of the OC with aggregates and BD were analyzed by cross-semivariogram. We could conclude that there was spatial dependence in the variables, wherein the largest ones were observed at 0.0-0.05 m, except for Mean Weighted Diameter (MWD) and aggregates greater than 2.00 mm with larger range of values in depth from 0.05-0.10 and 0.10-0.20 m. The mean weight diameter and aggregate class attributes greater than 2.00 mm had negative spatial correlation with organic carbon at 0.0-0.05 m, while the smaller aggregates than 2.00 mm classes and bulk density correlated positively with organic carbon at 0.0-0.05 m and 0.10-0.20 m.

Considerando a importância do conhecimento da variabilidade e correlação espacial dos atributos do solo em Terra Preta de Índio (TPIs), avaliou-se neste trabalho a variabilidade e a correlação espacial de agregados e carbono em um Argissolo Amarelo eutrófico sob cultivo de café na região sul do Amazonas. Foi estabelecido um grid amostral com dimensões de 48 x 88 m e espaçamentos de 06 x 08 m, totalizando 88 pontos amostrais. Em seguida, foram coletadas amostras de solos nas profundidades: 0,0-0,05, 0,05-0,10, e 0,10-0,20 m. A variabilidade espacial dos atributos diâmetro médio ponderado (DMP), agregados > 2 mm, < 2 mm, densidade do solo (Ds) e carbono orgânico (CO) foi analisada ajustando os semivariogramas simples, enquanto as correlações espaciais do CO com agregados e Ds foram analisadas por semivariogramas cruzados. Concluiu-se que as variáveis apresentaram dependência espacial, e os maiores alcances são constatados na profundidade 0,0-0,05 m, exceto para DMP e agregados maiores que 2,00 mm com maiores valores de alcance na profundidade 0,05-0,10 e 0,10-0,20 m. Os atributos diâmetro médio ponderado e classes de agregados maior que 2,00 mm apresentam correlação espacial negativa com carbono orgânico na profundidade 0,0-0,05 m, enquanto a classes de agregados menor que 2,00 mm e densidade do solo apresentam correlação positiva com carbono orgânico nas profundidades 0,0-0,05 m e 0,10-0,20 m.

Spatial variability of aggregates and organic carbon under three different uses of indian black earth in southern Amazonas / Variabilidade espacial de agregados e carbono orgânico sob três diferentes usos de terra preta de índio no sul do Amazonas

Indian Black Earths (IBEs) are distributed throughout the Amazon. They are characterized by their high chemical fertility and agricultural potential. IBEs have high organic carbon, favouring the improvement of soil structure. This work aimed to evaluate the aggregates and organic carbon (OC) spatial variability in different IBEs in southern Amazonas. We evaluated the organic carbon spatial variability, mean weight diameter (MWD), soil bulk density (b) and aggregate classes under three uses of soil: pasture, cocoa, and coffee. We collected 528 soil samples in a point grid according to its use at two depths: 0.0-0.05 m and 0.10-0.20 m. Results were subjected to variance, descriptive, and geostatistical analyses. We concluded that the soil use influenced the IBEs physical attributes soil behavior, concentrating the higher values of CO, aggregates > 2.00 mm, and MWD at 0.0-0.05 m in relation to b and aggregates < 2.00 mm where the higher values were the ones at 0.10-0.20 m. Aggregates < 2.00 mm (0.10-0.20 m) and OC (0.0-0.05 m) did not show spatial dependence, while the class of aggregates > 2.00 mm was the only attribute which represented to be a natural characteristic of the soil, with a strong spatial dependence, independently the land use and depth. There was no spatial relationship between the attributes studied and the geomorphic diversity.

As Terras Pretas de Índio (TPIs) encontram-se distribuídas por toda a Amazônia. Elas são caracterizadas pela alta fertilidade química e potencial agrícola. As TPIs possuem alto carbono orgânico, favorecendo a melhoria da estrutura do solo. Este trabalho teve como objetivo avaliar a variabilidade espacial dos agregados e do carbono orgânico (CO) em diferentes usos de TPIs no sul do Amazonas. Foi avaliado a variabilidade espacial do carbono orgânico, diâmetro médio ponderado (DMP), densidade do solo (b) e as classes de agregados sob três usos do solo: pastagem, cacau e café. Nas áreas estudas construiu-se um grid regular de pontos, de acordo com o uso do solo e nas profundidades, 0-0,05 m e 0,10-0,20 m, totalizando 528 amostras de solo. Os resultados foram submetidos à análise de variância, descritiva e geoestatística. O uso do solo influenciou o comportamento dos atributos físicos das TPIs, concentrando os valores mais altos de CO, agregados > 2.00 mm e DMP na profundidade 0,0-0.05 m em relação a b e agregados <2.00 mm, que assumiram valores mais altos na profundidade 0,10-0,20 m. Agregados < 2,00 mm (0,10-0,20 m) e CO (0,0-0,05 m) não apresentaram dependência espacial, enquanto a classe de agregados > 2,00 mm foi o único atributo que representou uma característica natural do solo, com forte dependência espacial, independentemente do uso e profundidade do solo. Não houve relação espacial entre os atributos estudados e a diversidade geomórfica.