Antônio Carlos Andrade Gonçalves

Estabilidade temporal da distribuição espacial da umidade do solo em área irrigada por pivô central

A heterogeneidade do solo faz com que o armazenamento de agua seja variavel, sendo necessaria uma amostragem intensa, para caracterizar a sua distribuicao espacial em uma area irrigada. Para fins de manejo da irrigacao, e importante o monitoramento da umidade do solo durante o processo de secagem entre duas irrigacoes sucessivas. O presente trabalho tem por objetivos avaliar a estabilidade temporal da distribuicao espacial da umidade do solo, a correlacao da umidade com conteudo de argila e avaliar se ha estrutura de dependencia espacial dessas variaveis. Quanto mais estavel for a distribuicao espacial da umidade e mais estreita a correlacao com a textura, menos intensas poderao ser as amostragens para fins de controle das irrigacoes. Em area irrigada por pivo central, no campus da ESALQ/USP, de solo Podzolico Vermelho-Escuro, a umidade foi medida em pontos espacados de 2,83xa0m ao longo de uma transecao radial, nas profundidades de 0,15 e 0,30xa0m, por meio de uma sonda de neutrons. O conteudo de argila e a densidade global foram tambem medidos. As medidas foram feitas durante um periodo de secagem do solo. A estabilidade temporal das distribuicoes espaciais foi avaliada por meio do coeficiente de correlacao e da tecnica de diferencas relativas. Foi constatada a persistencia no tempo das distribuicoes de umidade, sendo possivel identificar pontos de amostragem cujos valores permitem estimar a media geral da umidade na area, a qualquer momento. A dependencia espacial da umidade foi avaliada por meio de semivariogramas, os quais mostraram que mais de 50% da variacao dos dados pode ser atribuida a variacao estruturada no espaco, cujo padrao se mantem estavel no tempo e varia com a profundidade. Na camada inferior, a correlacao espacial entre umidade e conteudo de argila e descrita por semivariograma cruzado com efeito pepita nulo. A estrutura de dependencia espacial pode ser usada no mapeamento da umidade do solo.

Influência de diferentes sistemas de preparo do solo nas propriedades físicas de um Latossolo Vermelho distrófico

Em geral, os sistemas de preparo do solo tem, como objetivo, oferecer condicoes fisicas adequadas para a otimizacao do crescimento, desenvolvimento e produtividade das culturas. O proposito deste estudo foi avaliar o efeito dos sistemas de preparo do solo em algumas propriedades fisicas de um Latossolo Vermelho distrofico, no Estado do Parana, cultivado com mandioca. Para isto, utilizaram-se, neste trabalho, os seguintes tratamentos: Plantio Direto - PD (sem revolvimento do solo ou revolvimento apenas ao longo das linhas de plantio); Preparo Minimo - PM (escarificacao a 0,30 m seguido de gradagem niveladora) e Preparo Convencional - PC (aracao com arado de aiveca a 0,25-0,30 m de profundidade, seguido de gradagem niveladora). As avaliacoes feitas nas camadas de 0-0,15 e 0,15-0,30 m constaram das seguintes propriedades fisicas do solo: densidade do solo (Ds), volume de macroporos drenados na tensao de 0,006 MPa (Mac), volume de microporos (Mic) e porosidade total (Pt). Avaliou-se, tambem, a resistencia do solo a penetracao das raizes (RP) a cada 0,05 m, ate a profundidade de 0,40 m, em duas diferentes epocas, em que os resultados indicaram maiores valores de Ds e menores de Mac no PD e no PM em comparacao com o PC. No PM e PD constatou-se que o volume de poros com ar na tensao de 0,006 MPa foi menor que 10% e a RP foi maior no PD em comparacao com os demais tratamentos, atingindo valores superiores a 2,0 MPa, ate a profundidade de 0,25 m. Os resultados sugerem que, nas condicoes em que o estudo foi conduzido, a qualidade fisica do solo mostrou-se restritiva no PD devido aos excessivos valores de RP e aos reduzidos valores de porosidade de aeracao.

Determinação da permeabilidade ao ar em amostras indeformadas de solo pelo método da pressão decrescente

Soil air permeability (Ka) controls the convective gas flux in the soil matrix and at the soil-atmosphere interface, directly affecting the soil physical quality for plant growth and the rate of processes that depend on the soil gas concentration. Ka can be estimated by a simplified method based on a modification of Darcys law for gas flow in soil under decreasing pressure. The objective of this research was to modify and improve a permeameter for laboratory quantification of Ka by the falling pressure method. Two data acquisition systems were used for this purpose: an electronic-automatic system composed of a pressure transducer connected to a datalogger (E1) and alternatively, a system composed of a digital manometer for measuring the pressure decrease and a chronometer (E2). In E1, samples of the surface layer of a Nitossolo Vermelho eutroferrico (Alfisol) collected on the experimental farm of the Escola Superior de Agricultura Luiz de Queiroz - USP, Piracicaba, Sao Paulo, were evaluated, while in E2 samples of a Nitossolo Vermelho distroferrico profile from different depths, collected from the experimental farm of the Universidade Estadual de Maringa, Maringa, PR, were evaluated. The Ka tests were performed in undisturbed samples with variability in soil bulk density and water content. Overall Ka increased with decreasing soil water content and bulk density. This can be related to the increase in air-filled porosity volume with the decrease in these two variables. The results show that the apparatus is inexpensive, versatile, fast, and simple for Ka determination, independently of the data acquisition system.

Influência da condutividade elétrica, concentração iônica e vazão de soluções nutritivas na produção de alface hidropônica

Objetivou-se, neste trabalho, estudar os efeitos de diferentes solucoes nutritivas aplicadas em duas vazoes na producao hidroponica da alface (Lactuca sativa), cultivada pelo sistema NFT (Nutritive Film Technique). O experimento foi conduzido em casa de vegetacao, na unidade de pesquisa em agricultura irrigada da Universidade Estadual de Maringa. Os tratamentos constaram de tres solucoes nutritivas com concentracoes diferentes (S1=0,8 dS/m, S2=1,2 dS/m e S3=2,5 dS/m), combinadas com duas vazoes de aplicacao (V1=0,8 L.min-1 e V2=1,2 L.min-1 ) nos canais de cultivo em esquema fatorial 3 x 2. Para avaliar o efeito dos tratamentos no desenvolvimento da cultura os dados foram submetidos a analise de variância (teste F), e os resultados avaliados atraves de teste de media de Tukey (5%). A analise dos resultados permitiu concluir que os fatores solucao e vazao nao apresentaram interacao significativa e que os maiores valores avaliados de biomassa fresca e diâmetro do caule foram obtidos no tratamento solucao 2 (CE= 1,2 dS/m).

Padrões de amostragem e intensidade de krigagem na caracterização do armazenamento de água no solo, em área irrigada por pivô central

Irrigation quality has been described by calculated parameters assuming that water storage capacity in soil is a constant. However, this property presents spatial variations. Concern with environmental and economic aspects has led to culture management in specific areas, a fact which requires knowledge of spatial distribution of soil properties. Geostatistics makes possible the identification of the spatial dependence structure and the mapping of a given soil property. The objective of this work was to identify sampling and block kriging intensities, adequate to estimate soil water storage with enough precision to characterize irrigation quality. A radial transect was sampled each 2.83 m, in 56 locations in a center pivot-irrigated area at ESALQ/USP, Sao Paulo, Brazil. At each point, the water storage capacity in soil was determined at pressures varying between 0.01 and 0.08 MPa at 0-3 m depth. Based on the semivariogram obtained for the transect data, kriging was performed in blocks of different lengths varying between 2 and 30 m and simulated sampling spacings between 2 to 20 m, in the transect direction. From these values, the available soil water storage at 0.30 m soil profile was calculated. The block kriging variance and deep percolation water volume were obtained for each block kriging combination. To quantify deep percolation, it was assumed that the constant depth of applied irrigation was equal to the mean soil water storage. The results showed that block kriging must be performed with a 2 m block length, provided computer resources are not limiting factors. Increasing the soil sampling intensity did not promote interpolation. Thus, a 20 m grid may be used but a 10 m grid should be more appropriate. Short range sampling should be performed to identify the semivariogram at lower distances. Although it promoted smoothing, block kriging must be used to describe the spatial pattern of the soil water storage, since it allows a better evaluation of excess and deficit volumes and, mainly, the identification of the sites where they occur.

Variabilidade espacial da resistência do solo à penetração e da taxa de estratificação de carbono orgânico do solo em um Latossolo Vermelho eutroférrico

The compaction and the quality of the soil are constantly questioned for the definition of the no-till soil management. This study was aimed at evaluating the spatial variability of the soil resistance to penetration, bulk density and soil organic carbon stratification ratio in layers on a clayey Typic Eutrothox, in contiguous areas of no-tillage with rotation of cultures and no-tillage with succession of cultures associated the chiselling. The study was set up from May to June of 2002, in Palotina, west region of the state of Parana, Brazil. The samples for determination the soil bulk density, soil resistance to penetration and soil organic carbon stratification ratio were obtained in 120 points in 2 x 5m grid, in the 0.40m depth. Soil resistance to penetration measures were made three times, in a period of 10 days, initiate after having interrupted precipitation. The soil bulk density did not explain the spatial dependence of the compaction of the soil. The soil resistance to penetration and soil organic carbon stratification ratio presented range of 17m. The temporal variation of the spatial dependence of the soil resistance to penetration happens in the 0.05-0.20m layers. Similares spatial e dependence of the soil resistance to penetration and soil organic carbon stratification ratio reveals the importance of the quality of the soil in the spatial and temporary stabilization of the compaction of the soil expresses for the soil resistance to penetration in no-tillage systems.

Influência da densidade do solo na estimativa da umidade em um nitossolo vermelho distroférrico, por meio da técnica de TDR

Among the techniques for soil moisture evaluation, the use of Time Domain Reflectometry (TDR) stands out, which consists of an indirect, non-destructive, fast and accurate method less dependent on environmental factors. However, works carried out after its applications suggest the influence of factors related to soils structural and mineralogical characteristics, which makes necessary the site calibration for the TDR proper functioning. The aim of this work was to study the influence of bulk density (Ds) on the volumetric soil water content (θ), using the TDR technique in a Dystroferric Red Ultisol. A model that expresses the relationship between the soil dielectric constant (Ka) and θ was adjusted by multiple polynomial regression, with the incorporation of Ds for the estimation of its coefficients. The results showed that in this soil, the calibration model should take into account the effect of Ds, without which the quality of the moisture estimates from the dielectric constant measurements is compromised. The results also highlighted the high sensitivity of TDR to the variation of soil moisture, making it possible the accurate use of this technique in actions involving the monitoring of the variation in soil moisture. The results indicated the need for further studies on the use of TDR in tropical soils.

Spatial variability and temporal stability of water storage in a cultivated tropical soil

Irrigated agricultural fields usually show variable crop water demand. If water application is done to match this spatially variable demand, the water use efficiency can be substantially improved. Soil water management by irrigation has been one of the most important factors to increase crop yield. To look for the economic viability of the process, the use of several inputs, particularly water, should be done with high efficiency levels. Historically, irrigation uniformity has been evaluated above the soil surface, in which applied water was the only factor to be taken into account. However, the crop will respond to soil water content uniformity, which can differ from the uniformity of water application. To evaluate temporal stability of spatial pattern of soil water storage (SWS), this work was done on a Brazilian clayed soil. Volumetric water content from soil surface to 0,30m depth, was measured by TDR in 80 points regularly spaced (3 x 3 m) on an experimental area cultivated with bean crop, irrigated by conventional sprinkling. The evaluations were done immediately before and after a water application by irrigation. Experimental semivariograms made from values obtained in the field showed that SWS distribution was spatially structured and strongly stable in time, being regulated mainly by intrinsic factors of the soil. In addition, obtained results showed that water application uniformity did not influence the spatial distribution pattern of SWS in these soil conditions.