C. R. Grego

Variabilidade espacial da infiltração de água em solo sob pastagem em função da intensidade de pisoteio

The objective of this work was to evaluate the effect of cattle trampling intensity on the spatial variability of soil‑water infiltration rate. The experiment was carried out on an Argissolo Vermelho‑Amarelo (Ultisol) under a Urochloa brizantha pasture, divided into six one‑hectare plots, each with 50 sampling points in a 10x10 m grid. In each sampling site, the saturated three‑dimensional infiltration rate at 0.10 and 0.20‑m depths was measured. Measurements were made in the first, eleventh and fifteenth cattle passages on the plots. Data were submitted to geostatistics for the study of the spatial variability of the saturated infiltration rate. The 15 cattle passages on the plots caused a decrease of 73.3% in the soil water infiltration rate, at 0.10‑m depth, and 64.4% at 0.20‑m depth. The study of spatial variability of soil‑water infiltration rate with geostatistics permits the construction of maps for assessing the effects of cattle trampling intensification on soil physical properties. Water infiltration rate in soil has a spatial dependency structure which increases as a function of trampling intensity.

Abordagens semiquantitativa e quantitativa na avaliação da textura do solo por espectroscopia de reflectância bidirecional no VIS‑NIR‑SWIR

The objective of this work was to evaluate the potential of VIS‑NIR‑SWIR reflectance spectroscopy for the characterization of soil particle‑size distribution of samples from different textural classes, and to obtain models to predict clay, silt, and sand contents in the soil. A representative sample set of Oxisols and Ultisols from five locations in Mato Grosso do Sul state, Brazil, were used. Visible and near‑infrared to short‑wave infrared (from 350 to 2,500 nm) spectra of the samples were obtained and analyzed. Principal component analysis (PCA), fuzzy c‑means cluster analysis, multinomial logistic regression (MLR), and partial least squares regression were used. Characteristic spectra for the different soil texture classes and segregation of samples from texture classes and from sampling sites with distinct characteristics, through PCA, fuzzy c‑means, and RLM, show the semiquantitative potential of the VIS‑NIR‑SWIR reflectance data. Satisfactory quantification was obtained for clay (R²=0.92, RPD=3.59), silt (R²=0.80, RPD=2.15), and sand (R²=0.87, RPD=2.62). The reflectance spectroscopy techniques can help to assess soil texture and soil spacial variability with semiquantitative or quantitative methodologies.

Variabilidade espacial de atributos físicos de um argissolo vermelho-amarelo cultivado com leguminosas consorciada com a seringueira

O objetivo deste trabalho foi avaliar a distribuicao espacial de alguns atributos fisicos do solo e verificar suas alteracoes no desenvolvimento da seringueira consorciada com leguminosas. O experimento foi instalado em Argissolo Vermelho-Amarelo no Polo Regional de Desenvolvimento Tecnologico dos Agronegocios do Centro-Norte, localizado em Pindorama (SP). Foram avaliadas: infiltracao de agua a 0,10 e a 0,20 m de profundidade, macro e micro porosidade e densidade do solo nas camadas 0-0,10; 0,10-0,20; 0,20-0,40 e 0,40-0,60 m. O desenvolvimento das plantas de seringueira foi avaliado medindo-se o perimetro do caule e o aumento desta medida no periodo de quatro anos (1996-1999). Os dados foram submetidos a analise de estatistica descritiva para verificacao de parâmetros de tendencia central e dispersao. Foram utilizados metodos geoestatisticos incluindo semivariogramas, krigagem e mapas de isolinhas para a avaliacao da variabilidade espacial. Houve dependencia espacial de moderada a forte para todos os atributos do solo, com o valor do alcance variando entre 15 e 90 m. A dependencia espacial anotada para infiltracao de agua no solo nao teve relacao com as avaliacoes efetuadas nas plantas nem com os outros atributos avaliados. Os altos valores de densidade do solo e de microporosidade na camada de 0,20-0,40 m indicaram a ocorrencia de compactacao nesta camada. O perimetro do caule de seringueira aumentou linearmente com o tempo, porem a taxa de crescimento do perimetro do caule decresceu ao longo dos anos. A taxa media de crescimento do perimetro do caule variou em funcao do crescimento menor no inverno quando comparado com o do verao. Na distribuicao espacial do espessamento do caule das arvores de seringueira ao longo do tempo houve alta continuidade, avaliada pelos baixos valores do efeito pepita dos semivariogramas e estreita correlacao com densidade do solo, onde locais menos densos tiveram os maiores valores para o perimetro do caule da seringueira.

Distribuição espacial de fósforo em Latossolo tratado com lodo de esgoto e adubação mineral

In agricultural soils receiving sewage sludge and subjected to water erosion, may occur intense transport of phosphorus (P) to the lower parts of the landscape and eventually to water bodies. The objective of this study was to evaluate the spatial distribution of P in an Oxisol cultivated with maize. The treatments were evaluated with application of mineral fertilization (MF) and sewage sludge (SS). Soil samples were collected following a sampling grid of 69 points in each treatment at the beginning and at the end of the crop cycle, in an experimental area with 10% slope. There was a moderate spatial dependence of P in the soil in the treatment of MF, resulting in higher concentrations of P in the deeper layers of the soil caused by erosion. The same standard was observed for the soil attributes sum of bases, cation exchange capacity and soil organic matter. Conversely, when SS was applied there was a randomized distribution of P in the plots because of the non-uniform manner of its application. Such random distribution of P showed correlation with soil organic matter.

Variabilidade espacial de parâmetros físico-químicas do solo e biofísicos de superfície em cultivo do sorgo

O conhecimento da variabilidade espacial das propriedades do solo e das culturas e importante para as tomadas de decisao sobre o manejo agricola. Objetivou-se, neste trabalho, avaliar a variabilidade espacial de parâmetros quimicos e fisicos do solo e biofisicos de superficie de area cultivada com sorgo. O estudo foi conduzido em area de 12 ha de um Argissolo Vermelho Amarelo distrofico. A amostragem de solo georreferenciada e a medicao da condutividade eletrica do solo foram realizadas antes do plantio do sorgo. As imagens do satelite Landsat 5 foram utilizadas para calcular os parâmetros biofisicos de superficie. Ferramentas de geoestatistica foram utilizadas para se determinar e modelar a variabilidade espacial dos atributos em estudo em que os resultados mostraram que a densidade de amostragem adotada foi insuficiente para uma caracterizacao adequada da variabilidade espacial de parâmetros do solo. Ocorreu dependencia espacial de grau, moderada a forte para CE e parâmetros biofisicos da superficie da imagem de satelite com alcances variando de 74,4 a 181,1 m; por outro lado, o sensoriamento remoto orbital tambem foi util para o mapeamento da variabilidade espacial da cultura do sorgo e tem grande potencial para aplicacao da Agricultura de Precisao.

Modelo multicritério aditivo na geração de mapas de suscetibilidade à erosão em área rural

The objective of this work was to evaluate the construction of an erosion susceptibility map for a rural area of the municipality of Guararapes, SP, Brazil, using a multicriteria additive model. Digital maps on the themes relief (declivity and length of the slopes), pedology (obtained at the field), land use and land cover of the region, and interpretation of the digital elevation model were used. The digital maps were treated in a geographic information system environment using the additive multicriteria method and were validated by the universal soil loss equation (USLE) model. Five erosion susceptibility classes were generated: low, moderate, high, very high, and extremely high. The risk map obtained by additive multicriteria had good correspondence with the USLE model. The erosion susceptibility map can be used for the agricultural and environmental planning of the rural area of the municipality of Guararapes.

Variabilidade espacial do solo e da biomassa epígea de pastagem, identificada por meio de geostatística

O objetivo deste trabalho foi identificar a estrutura de dependencia espacial de atributos do solo e sua interferencia na producao de biomassa epigea de pastagem de capim‑marandu (Urochloa brizantha). Amostras de Latossolo Vermelho‑Amarelo foram coletadas em rede de pontos georreferenciados, para a determinacao de atributos fisicos e quimicos do solo e da producao de biomassa epigea da pastagem, no verao e outono de 2010/2011. Verificou-se dependencia espacial das variaveis, por meio de analise geoestatistica com construcao e ajuste de semivariogramas, interpolacao por krigagem ordinaria e espacializacao em mapas de isolinhas. A dependencia espacial ocorreu para alguns atributos fisicos e quimicos do solo (areia, densidade, resistencia a penetracao, infiltracao, pH, MO, P, K, Ca, Mg, H+Al, Al, CTC e V), e para a biomassa da pastagem medida nas estacoes verao e outono. A analise espacial de atributos fisicos do solo permite identificar areas degradadas da pastagem. A biomassa da pastagem e mais influenciada pelos atributos fisicos do solo do que pelos quimicos.

ANALYZING SPATIAL AND TEMPORAL VARIABILITY OF SOIL WATER CONTENT ( 1 )

During the last two decades geoestatistical methods have been intensively used for in-depth descriptions of spatial variability. The objective of this study was to assess the spatial and temporal variability of soil water content. The measurements were taken with a TDR equipment to a 20 cm depth, in a nearly flat 1.2 ha field at the Central Experimental Farm of the Agriculture Canada, Ottawa. The soil classified as a Rideau soil series, is a clay loam soil. A square grid with 10 m spacing was laid out, resulting in 164 sampling points at which two TDR rods were installed to measure the water content down to 20 cm depth. Measurements were taken on 33 dates during the frost free months in 1987, 1988 and 1989. The spatial variability was analyzed examining the scaled semivariograms, the statistical parameters and the parameters of the models fit to individual semivariograms as a function of time. It was concluded that spatial dependence decreases as the soil gets drier and that results from one year connect almost continuously to other years. The topography and structure of topsoil horizon was the primary cause for the repeating spatial pattern of soil water content in successive samplings. The places where the mean value occurred in the field were more stable in time when there was spatial dependence. As the soil gets dryer the temporal stability of the spatial distribution tends to disappear due to the hydraulic conductivity controlling the water evaporation over the field.

Geostatistical analysis of crop yield maps in a long term no tillage system

It is known, for a long time, that crop yields are not uniform at the field. In some places, it is possible to distinguish sites with both low and high yields even within the same area. This work aimed to evaluate the spatial and temporal variability of some crop yields and to identify potential zones for site specific management in an area under no-tillage system for 23 years. Data were analyzed from a 3.42 ha long term experimental area at the Centro Experimental Central of the Instituto Agronomico, located in Campinas, Sao Paulo State, Brazil. The crop yield data evaluated included the following crops: soybean, maize, lablab and triticale, and all of them were cultivated since 1985 and sampled at a regular grid of 302 points. Data were normalized and analyzed using descriptive statistics and geostatistical tools in order to demonstrate and describe the structure of the spatial variability. All crop yields showed high variability. All of them also showed spatial dependence and were fitted to the spherical model, except for the yield of the maize in 1999 productivity which was fitted to the exponential model. The north part of the area presented repeated high values of productivity in some years. There was a positive cross correlation amongst the productivity values, especially for the maize crops.

Spatial variability of some biometricattributes of sugarcane plants (variety IACSP93-3046) and its relation to physical and chemical soil attributes

Tests to evaluate competition between plants, in general do not consider the soil spatial variability, nevertheless, the uniformity rarely is present and can not be assumed without verification. The aim of this work was to apply geostatistics to verify the spatial variability of the soil in an experimental field near Ribeirao Preto, SP, with sugarcane variety IACSP93-3046. Ninety seven geo-referenced samples, placed at distances of 10 m, were collected for soil chemical analysis, soil resistance to penetration and biometric evaluation of the sugar cane plant included number of tillers, stalk diameter, stalk height, estimated productivity (TSSe) and root density. Geostatistics has been applied by means of semivariogram, data interpolation via kriging and iso-line maps creation. The results have shown soil spatial dependence for most of the evaluated attributes. The spots, within the area, with low resistance to penetration and low soil density have shown the largest number of tillers and the largest root development of sugar cane. For soil chemical attributes, there was spatial dependence showing higher concentration of nutrients in the central area. The sampling allowed a good representativity of the spatial dependence of soil and plants, making it possible to eliminate the randomness hypothesis for the placement of the plots in this area.