O terraceamento é uma prática de conservação do solo que visa reduzir a perda de água e solo pela interceptação de enxurradas que ocorrem quando a intensidade da chuva supera a capacidade de infiltração de água no solo. Atualmente, o dimensionamento dos terraços tem sido feito com base em conhecimento empírico; no entanto, um conhecimento mais detalhado da física dos processos que regem o funcionamento dos terraços possibilitaria otimizar o dimensionamento dos terraços. No presente estudo foi avaliada a capacidade de infiltração de água no canal de um terraço em nível pelos métodos da densidade de fluxo e da armazenagem de água em diferentes condições de manejo agrícola (solo nu, solo gramado e solo sob preparo convencional e plantio direto para a implantação da cultura de milho) num Latossolo vermelho com declividade média de 0,08 m m-1. Em cada tratamento foram instaladas sondas de TDR em três pontos de observação no centro do canal do terraço (distanciados de 4 m entre si e considerados como repetições), nas rofundidades de 0,05, 0,10, 0,20, 0,40, 0,60 e 0,80 m. Nestas mesmas profundidades amostras indeformadas de solo foram retiradas para determinação da densidade e curva de retenção de água no solo. As leituras das guias de onda do TDR foram feitas automaticamente e a intensidade de chuva monitorada por um pluviômetro automatizado. Ao final de cada evento de chuva erosiva a deposição de solo foi medida por meio de 14 pontos de observação dispostos ao longo do centro do canal do terraço de cada tratamento. Durante a estação seca (julho-agosto), a condutividade hidráulica do solo não saturado foi determinada em cada repetição nas mesmas profundidades, utilizando o método do perfil instantâneo. Os resultados demonstraram que os manejos agrícolas influenciam na deposição de água e solo sobre o canal do terraço e estas na formação de selo superficial e na capacidade de infiltração de água do canal. Conclui-se que a alta variação comumente obtida entre as repetições de determinação da condutividade hidráulica implica em dificuldades quando se objetiva detectar pequenas diferenças nas densidades de fluxo entre tratamentos. Assim, mostrou ser inviável utilizar densidades de fluxo calculadas pela equação de Darcy-Buckingham para encontrar diferenças em taxas de infiltração em terraços em nível. Essa conclusão reforça-se devido às condições superficiais altamente variáveis encontradas em canais de terraços em nível devido a deposições irregulares do material erodido. Uma metodologia para se realizar medições da umidade nas deposições sobre o canal deve ser desenvolvida para aumentar a acurácia da medida da armazenagem. A taxa de infiltração de água no canal do terraço não pode ser estimada pela variação da armazenagem da água no solo somente, devido ao papel importante da drenagem profunda e, possivelmente, da absorção de água pela camalhão do terraço. Uma adequada estimativa da taxa de infiltração no canal do terraço, imprescindível para seu dimensionamento, deve aliar um grande número de repetições, além da medição da umidade no interior da camada de material depositado sobre o canal ao longo do tempo. / Terracing is a soil conservation practice that aims to reduce water and soil loss by interception of runoff that occurs when rainfall intensities exceed infiltration capacity. Actually, dimensions of terraces are being determined in an empirical way; however, a more detailed understanding of the physics behind the hydrological functions of terraces would allow an optimized dimensioning of terraces. In this study the infiltration capacity of a level terrace was evaluated by the methods of flux density and water storage, under different management conditions (bare soil, pasture, conventionally tilled maize and zero-tillage maize) on an oxisol with a slope of 0.08 m m-1. In each treatment TDR sensors were installed at three observation points in the middle of the terrace canal (distance between points: 4 m; considered to be repetitions) at the depths of 0.05, 0.10, 0.20, 0.40, 0.60 and 0.80 m. At the same depths, undisturbed soil samples were taken to determine soil density and soil water retention curve. TDR readings were made automatically and a rainfall gauge automatically monitored rainfall intensity. At the end of each rainfall event, soil deposition was measured at 14 locations in the terrace canal in each treatment. During the dry season (July-August), unsaturated hydraulic conductivity was determined at each repetition at the same depths by the instantaneous profile method. The results showed that agricultural management influenced water and soil deposition in the terrace canal and these affected surfaced sealing and infiltration capacity. It was concluded that the high variation usually obtained between repetitions of the hydraulic conductivity determinations makes the detection of small differences between flux densities difficult. Therefore, it showed to be impossible to use flux densities calculated by Darcy-Buckingham equation in the order to prove existence of different infiltration rates in level terraces. This conclusion was reinforced due to the highly variable surface conditions in the terrace canal. A methodology to measure water contents within the depositions in the canal should be developed to increase the precision of water storage estimation. Infiltration rates in the terrace canal cannot be estimated by storage variation alone, due to the important role of drainage and, possibly, ascension of water in the terrace hill. A correct estimate of the infiltration rate in the canal, necessary for its dimensioning, should combine a high number of repetitions with the measurement of water content within the layer of deposits over the terrace canal surface along time.

O entendimento dos processos hídricos do solo, tais como infiltração, drenagem, e disponibilidade de água para as plantas, necessita do conhecimento da relação entre o conteúdo de água no solo e o potencial matricial, representado pela curva de retenção de água no solo (CRA). No entanto, a determinação da CRA demanda tempo e possui um custo relativo alto. Uma alternativa é sua determinação através de modelos que estimam a CRA a partir de alguns atributos de fácil determinação, chamados funções de pedotransferência (FPT). A finalidade desse trabalho foi quantificar os efeitos da mudança do uso do solo sobre os atributos físicos e hídricos no Sudeste do Estado do Pará. Utilizou-se o banco de dados do Projeto Serviços ecossistêmicos e sustentabilidade das paisagens agrosilvipastoris da Amazônia Oriental, para obter dados de textura (areia, silte e argila), densidade do solo (Ds), carbono orgânico (CO), pH, capacidade de troca de cátions (CTC) e, as vezes, as CRA. Primeiramente, foram avaliadas 16 FPT existentes na literatura; 8 FPT paramétricas, que estimam os parâmetros empíricos do modelo de van Genuchten e 8 FPT pontuais, que estimam a umidade em potenciais específicos de água no solo. Posteriormente, buscando maior capacidade preditiva das FPT, através da técnica de regressão múltipla, desenvolveu-se uma FPT utilizando os atributos do solo mensurados no projeto. As melhores FPT foram utilizadas para estimar os parâmetros do modelo de van Genuchten nos sítios onde não havia CRA medida. Através desta extrapolação, avaliou-se o efeito da mudança de uso do solo sobre a distribuição dos tamanhos de poros, utilizando-se análise de componentes principais (ACP). Dentre as FPT testadas, as que apresentaram melhor resultado foram as FPT propostas por Tomasella et al. (2000), no entanto, a avaliação de desempenho realizada mostrou resultados não satisfatórios. Por outro lado, os resultados apresentados pela FPT desenvolvida neste trabalho alcançaram boa capacidade preditiva dos parâmetros empíricos do modelo de van Genuchten (1980). A ACP possibilitou identificar uma grande variabilidade entre os atributos medidos e estimados dos solos. Devido a esta variabilidade, não foram detectadas diferenças marcantes nos atributos dos solos em função do uso. Para isso, faz-se necessário estudos complementares, aumentando a escala e/ou classes de solo. / The understanding of soil water attributes, such as infiltration, drainage, solute movement and water availability for plants, needs the knowledge of the relationship between water content and soil matric potential, represented by the soil water retention curve (SWRC). However, the determination of the SWRC demands considerable time and has a relatively high cost. An alternative is to model its determination using pedotransfer functions (PTF) that calculate the SWRC parameters using easily obtainable soil attributes. The aim of this study was to use PTF to quantify the effects of changing land use on soil hydro-physical attributes at three locations in southern Pará. The database obtained in the project \"Ecosystem services and sustainable agroforestry landscapes in Eastern Amazonia\" was used in order to obtain soil texture data (sand, silt and clay), bulk density (Bd), organic carbon (OC), pH, cation exchange capacity (CEC) and the SWRC. First, 16 PTF found in the literature were evaluated (8 estimating the empirical parameters of the van Genuchten (1980) model and 8 to estimate soil moisture at specific matric potentials). Later, aiming at a greater predictive ability, a PTF was developed using the technique of multiple regression and the soil attributes determined in the project. The best PTF were used to estimate the model parameters of van Genuchten (1980) at the locations where there was no SWRC data. These results were used to determine the changes in pore distribution due to land use using principal component analysis (PCA). These changes were also associated with changes in content of OC and Bd using multivariate analysis. Of the FPT found in the literature the one that showed the best performance was the FPT developed by Tomasella et al. (2000), however, the evaluation performed showed poor results when the data was extrapolated to the locations where no SWRC were determined. The results presented by the FPT developed in this work showed a better efficiency in determining the SWRC in the locations that did not have this information. The PCA analysis performed on this data identified a large variability among the measured and estimated soil attributes. Because of this variability, there were no marked differences in soil attributes depending on land use. For this, more detailed studies are necessary at a increasing scale and/or at the soil class level.

Estudos mostram que ocorre uma compactação superficial após alguns anos de utilização do sistema plantio direto (SPD), podendo interferir no desenvolvimento das plantas. A escarificação tem sido utilizada para amenizar os efeitos da compactação sob SPD, porém há evidências de que seus efeitos são de curta duração. O objetivo deste trabalho foi avaliar o comportamento de alguns parâmetros físicos após a escarificação em curto prazo (um ano) nas seguintes profundidades: 0,0-0,10 m; 0,10-0,20 m; 0,20-0,30 m; 0,30-0,40 m. A densidade do solo (Ds) e o grau de compactação (Gc) foram analisados em área de plantio direto por 16 anos (PD), imediatamente após a escarificação (ESC), seis meses (ESC6M) e um ano após a escarificação (ESC12M). Nas camadas superiores a densidade do solo apresentou variação semelhante, com redução significativa em ESC e um aumento expressivo em ESC6M, sendo que a Ds retornou aos valores registrados antes da mobilização em ESC12M. Nos períodos ESC, ESC6M e ESC12M foi observado um aumento da Ds na camada 0,30-0,40 m em comparação com o PD. A escarificação provocou redução do grau de compactação nas camadas 0,0-0,10 m e 0,10-0,20 m, com o Gc retornando aos valores originais um ano após a escarificação. Os maiores valores de Gc foram observados seis meses após a escarificação, porém o solo apresentou grande recuperação visto que em ESC12M o grau de compactação apresentou tendência de retorno aos valores originais em todas as profundidades, possivelmente devido à alta resiliência do solo. Os efeitos da escarificação avaliados pela Ds e Gc apresentaram duração inferior a um ano, sugerindo que neste solo não é necessária esta operação. / Studies show that a surface compaction occurs after some years adoption of no-tillage (NT), which may interfere in plant development. Chiseling has been used to alleviate the effects of soil compaction under NT, but studies show that this operation has short-term effects. The aim of this study was to evaluate the behavior of some physical parameters after chiseling in shortterm (one year) in the following depths: 0.0 to 0.10 m, 0.10-0.20 m, 0.20-0, 30 m, 0.30 to 0.40 m. Soil bulk density (BD) and the degree of compactness (DC) were analyzed in long-term (16 years) no-tillage (NT), chiseling of the long-term no-tillage (CHI), six months (CHI6M) and one year after chiseling (CHI12M). In top layers bulk density showed similar variation, with significant reduction in CHI and a marked increase in CHI6M, returning to the values recorded before mobilization in CHI12M. In periods CHI, CHI6M and CHI12M was an increase in the BD 0.30-0.40 m layer in comparison with NT. Chiseling caused a reduction the degree of compaction in the layers 0.0-0.10 m and 0.10-0.20 m, with DC returning to the original values one year after chiseling. The greatest DC values were observed six months after chiseling, nevertheless the soil showed great recovery whereas in CHI12M the degree of compactness tended to return to the original values in all layers, possibly due the high soil resilience. The duration of chiseling effects measured by BD and DC was less than one year, suggesting in this soil is not necessary this operation.

O entendimento dos processos hídricos do solo, tais como infiltração, drenagem, e disponibilidade de água para as plantas, necessita do conhecimento da relação entre o conteúdo de água no solo e o potencial matricial, representado pela curva de retenção de água no solo (CRA). No entanto, a determinação da CRA demanda tempo e possui um custo relativo alto. Uma alternativa é sua determinação através de modelos que estimam a CRA a partir de alguns atributos de fácil determinação, chamados funções de pedotransferência (FPT). A finalidade desse trabalho foi quantificar os efeitos da mudança do uso do solo sobre os atributos físicos e hídricos no Sudeste do Estado do Pará. Utilizou-se o banco de dados do Projeto Serviços ecossistêmicos e sustentabilidade das paisagens agrosilvipastoris da Amazônia Oriental, para obter dados de textura (areia, silte e argila), densidade do solo (Ds), carbono orgânico (CO), pH, capacidade de troca de cátions (CTC) e, as vezes, as CRA. Primeiramente, foram avaliadas 16 FPT existentes na literatura; 8 FPT paramétricas, que estimam os parâmetros empíricos do modelo de van Genuchten e 8 FPT pontuais, que estimam a umidade em potenciais específicos de água no solo. Posteriormente, buscando maior capacidade preditiva das FPT, através da técnica de regressão múltipla, desenvolveu-se uma FPT utilizando os atributos do solo mensurados no projeto. As melhores FPT foram utilizadas para estimar os parâmetros do modelo de van Genuchten nos sítios onde não havia CRA medida. Através desta extrapolação, avaliou-se o efeito da mudança de uso do solo sobre a distribuição dos tamanhos de poros, utilizando-se análise de componentes principais (ACP). Dentre as FPT testadas, as que apresentaram melhor resultado foram as FPT propostas por Tomasella et al. (2000), no entanto, a avaliação de desempenho realizada mostrou resultados não satisfatórios. Por outro lado, os resultados apresentados pela FPT desenvolvida neste trabalho alcançaram boa capacidade preditiva dos parâmetros empíricos do modelo de van Genuchten (1980). A ACP possibilitou identificar uma grande variabilidade entre os atributos medidos e estimados dos solos. Devido a esta variabilidade, não foram detectadas diferenças marcantes nos atributos dos solos em função do uso. Para isso, faz-se necessário estudos complementares, aumentando a escala e/ou classes de solo. / The understanding of soil water attributes, such as infiltration, drainage, solute movement and water availability for plants, needs the knowledge of the relationship between water content and soil matric potential, represented by the soil water retention curve (SWRC). However, the determination of the SWRC demands considerable time and has a relatively high cost. An alternative is to model its determination using pedotransfer functions (PTF) that calculate the SWRC parameters using easily obtainable soil attributes. The aim of this study was to use PTF to quantify the effects of changing land use on soil hydro-physical attributes at three locations in southern Pará. The database obtained in the project \"Ecosystem services and sustainable agroforestry landscapes in Eastern Amazonia\" was used in order to obtain soil texture data (sand, silt and clay), bulk density (Bd), organic carbon (OC), pH, cation exchange capacity (CEC) and the SWRC. First, 16 PTF found in the literature were evaluated (8 estimating the empirical parameters of the van Genuchten (1980) model and 8 to estimate soil moisture at specific matric potentials). Later, aiming at a greater predictive ability, a PTF was developed using the technique of multiple regression and the soil attributes determined in the project. The best PTF were used to estimate the model parameters of van Genuchten (1980) at the locations where there was no SWRC data. These results were used to determine the changes in pore distribution due to land use using principal component analysis (PCA). These changes were also associated with changes in content of OC and Bd using multivariate analysis. Of the FPT found in the literature the one that showed the best performance was the FPT developed by Tomasella et al. (2000), however, the evaluation performed showed poor results when the data was extrapolated to the locations where no SWRC were determined. The results presented by the FPT developed in this work showed a better efficiency in determining the SWRC in the locations that did not have this information. The PCA analysis performed on this data identified a large variability among the measured and estimated soil attributes. Because of this variability, there were no marked differences in soil attributes depending on land use. For this, more detailed studies are necessary at a increasing scale and/or at the soil class level.

O terraceamento é uma prática de conservação do solo que visa reduzir a perda de água e solo pela interceptação de enxurradas que ocorrem quando a intensidade da chuva supera a capacidade de infiltração de água no solo. Atualmente, o dimensionamento dos terraços tem sido feito com base em conhecimento empírico; no entanto, um conhecimento mais detalhado da física dos processos que regem o funcionamento dos terraços possibilitaria otimizar o dimensionamento dos terraços. No presente estudo foi avaliada a capacidade de infiltração de água no canal de um terraço em nível pelos métodos da densidade de fluxo e da armazenagem de água em diferentes condições de manejo agrícola (solo nu, solo gramado e solo sob preparo convencional e plantio direto para a implantação da cultura de milho) num Latossolo vermelho com declividade média de 0,08 m m-1. Em cada tratamento foram instaladas sondas de TDR em três pontos de observação no centro do canal do terraço (distanciados de 4 m entre si e considerados como repetições), nas rofundidades de 0,05, 0,10, 0,20, 0,40, 0,60 e 0,80 m. Nestas mesmas profundidades amostras indeformadas de solo foram retiradas para determinação da densidade e curva de retenção de água no solo. As leituras das guias de onda do TDR foram feitas automaticamente e a intensidade de chuva monitorada por um pluviômetro automatizado. Ao final de cada evento de chuva erosiva a deposição de solo foi medida por meio de 14 pontos de observação dispostos ao longo do centro do canal do terraço de cada tratamento. Durante a estação seca (julho-agosto), a condutividade hidráulica do solo não saturado foi determinada em cada repetição nas mesmas profundidades, utilizando o método do perfil instantâneo. Os resultados demonstraram que os manejos agrícolas influenciam na deposição de água e solo sobre o canal do terraço e estas na formação de selo superficial e na capacidade de infiltração de água do canal. Conclui-se que a alta variação comumente obtida entre as repetições de determinação da condutividade hidráulica implica em dificuldades quando se objetiva detectar pequenas diferenças nas densidades de fluxo entre tratamentos. Assim, mostrou ser inviável utilizar densidades de fluxo calculadas pela equação de Darcy-Buckingham para encontrar diferenças em taxas de infiltração em terraços em nível. Essa conclusão reforça-se devido às condições superficiais altamente variáveis encontradas em canais de terraços em nível devido a deposições irregulares do material erodido. Uma metodologia para se realizar medições da umidade nas deposições sobre o canal deve ser desenvolvida para aumentar a acurácia da medida da armazenagem. A taxa de infiltração de água no canal do terraço não pode ser estimada pela variação da armazenagem da água no solo somente, devido ao papel importante da drenagem profunda e, possivelmente, da absorção de água pela camalhão do terraço. Uma adequada estimativa da taxa de infiltração no canal do terraço, imprescindível para seu dimensionamento, deve aliar um grande número de repetições, além da medição da umidade no interior da camada de material depositado sobre o canal ao longo do tempo. / Terracing is a soil conservation practice that aims to reduce water and soil loss by interception of runoff that occurs when rainfall intensities exceed infiltration capacity. Actually, dimensions of terraces are being determined in an empirical way; however, a more detailed understanding of the physics behind the hydrological functions of terraces would allow an optimized dimensioning of terraces. In this study the infiltration capacity of a level terrace was evaluated by the methods of flux density and water storage, under different management conditions (bare soil, pasture, conventionally tilled maize and zero-tillage maize) on an oxisol with a slope of 0.08 m m-1. In each treatment TDR sensors were installed at three observation points in the middle of the terrace canal (distance between points: 4 m; considered to be repetitions) at the depths of 0.05, 0.10, 0.20, 0.40, 0.60 and 0.80 m. At the same depths, undisturbed soil samples were taken to determine soil density and soil water retention curve. TDR readings were made automatically and a rainfall gauge automatically monitored rainfall intensity. At the end of each rainfall event, soil deposition was measured at 14 locations in the terrace canal in each treatment. During the dry season (July-August), unsaturated hydraulic conductivity was determined at each repetition at the same depths by the instantaneous profile method. The results showed that agricultural management influenced water and soil deposition in the terrace canal and these affected surfaced sealing and infiltration capacity. It was concluded that the high variation usually obtained between repetitions of the hydraulic conductivity determinations makes the detection of small differences between flux densities difficult. Therefore, it showed to be impossible to use flux densities calculated by Darcy-Buckingham equation in the order to prove existence of different infiltration rates in level terraces. This conclusion was reinforced due to the highly variable surface conditions in the terrace canal. A methodology to measure water contents within the depositions in the canal should be developed to increase the precision of water storage estimation. Infiltration rates in the terrace canal cannot be estimated by storage variation alone, due to the important role of drainage and, possibly, ascension of water in the terrace hill. A correct estimate of the infiltration rate in the canal, necessary for its dimensioning, should combine a high number of repetitions with the measurement of water content within the layer of deposits over the terrace canal surface along time.

Estudos mostram que ocorre uma compactação superficial após alguns anos de utilização do sistema plantio direto (SPD), podendo interferir no desenvolvimento das plantas. A escarificação tem sido utilizada para amenizar os efeitos da compactação sob SPD, porém há evidências de que seus efeitos são de curta duração. O objetivo deste trabalho foi avaliar o comportamento de alguns parâmetros físicos após a escarificação em curto prazo (um ano) nas seguintes profundidades: 0,0-0,10 m; 0,10-0,20 m; 0,20-0,30 m; 0,30-0,40 m. A densidade do solo (Ds) e o grau de compactação (Gc) foram analisados em área de plantio direto por 16 anos (PD), imediatamente após a escarificação (ESC), seis meses (ESC6M) e um ano após a escarificação (ESC12M). Nas camadas superiores a densidade do solo apresentou variação semelhante, com redução significativa em ESC e um aumento expressivo em ESC6M, sendo que a Ds retornou aos valores registrados antes da mobilização em ESC12M. Nos períodos ESC, ESC6M e ESC12M foi observado um aumento da Ds na camada 0,30-0,40 m em comparação com o PD. A escarificação provocou redução do grau de compactação nas camadas 0,0-0,10 m e 0,10-0,20 m, com o Gc retornando aos valores originais um ano após a escarificação. Os maiores valores de Gc foram observados seis meses após a escarificação, porém o solo apresentou grande recuperação visto que em ESC12M o grau de compactação apresentou tendência de retorno aos valores originais em todas as profundidades, possivelmente devido à alta resiliência do solo. Os efeitos da escarificação avaliados pela Ds e Gc apresentaram duração inferior a um ano, sugerindo que neste solo não é necessária esta operação. / Studies show that a surface compaction occurs after some years adoption of no-tillage (NT), which may interfere in plant development. Chiseling has been used to alleviate the effects of soil compaction under NT, but studies show that this operation has short-term effects. The aim of this study was to evaluate the behavior of some physical parameters after chiseling in shortterm (one year) in the following depths: 0.0 to 0.10 m, 0.10-0.20 m, 0.20-0, 30 m, 0.30 to 0.40 m. Soil bulk density (BD) and the degree of compactness (DC) were analyzed in long-term (16 years) no-tillage (NT), chiseling of the long-term no-tillage (CHI), six months (CHI6M) and one year after chiseling (CHI12M). In top layers bulk density showed similar variation, with significant reduction in CHI and a marked increase in CHI6M, returning to the values recorded before mobilization in CHI12M. In periods CHI, CHI6M and CHI12M was an increase in the BD 0.30-0.40 m layer in comparison with NT. Chiseling caused a reduction the degree of compaction in the layers 0.0-0.10 m and 0.10-0.20 m, with DC returning to the original values one year after chiseling. The greatest DC values were observed six months after chiseling, nevertheless the soil showed great recovery whereas in CHI12M the degree of compactness tended to return to the original values in all layers, possibly due the high soil resilience. The duration of chiseling effects measured by BD and DC was less than one year, suggesting in this soil is not necessary this operation.

Irrigation needs to be applied to soils in relatively humid regions such as western Kentucky to supply water for crop uptake to optimize and stabilize yields. Characterization of soil and crop variability at the field scale is needed to apply site specific management and to optimize water application. The objective of this work is to propose a characterization and modeling of soil and crop processes to improve irrigation management. Through an analysis of spatial and temporal behavior of soil and crop variables the variability in the field was identified. Integrative analysis of soil, crop, proximal and remote sensing data was utilized. A set of direct and indirect measurements that included soil texture, electrical conductivity (EC), soil chemical properties (pH, organic matter, N, P, K, Ca, Mg and Zn), NDVI, topographic variables, were measured in a silty loam soil near Princeton, Kentucky. Maps of measured properties were developed using kriging, and cokriging. Different approaches and two cluster methods (FANNY and CLARA) with selected variables were applied to identify management zones. Optimal scenarios were achieved with dividing the entire field into 2 or 3 areas. Spatial variability in the field is strongly influenced by topography and clay content. Using Root Zone Water Quality Model 2.0 (RZWQM), soil water tension was modeled and predicted at different zones based on the previous delineated zones. Soil water tension was measured at three depths (20, 40 and 60 cm) during different seasons (20016 and 2017) under wheat and corn. Temporal variations in soil water were driven mainly by precipitation but the behavior is different among management zones. The zone with higher clay content tends to dry out faster between rainfall events and reveals higher fluctuations in water tension even at greater depth. The other zones are more stable at the lower depth and share more similarities in their cyclic patterns. The model predictions were satisfactory in the surface layer but the accuracy decreased in deeper layers. A study of clay mineralogy was performed to explore field spatial differences based on the map classification. kaolinite, vermiculite, HIV and smectite are among the identified minerals. The clayey area presents higher quantity of some of the clay minerals. All these results show the ability to identify and characterize the field spatial variability, combining easily obtainable data under realistic farm conditions. This information can be utilized to manage resources more effectively through site specific application.

The aim of the thesis is to find a method, in conjunction with the ordinary differential equation (ODE) based method of lines (MOL) solution of Richards’ equation, to model the steep wetting front infiltration in very dry soils, accurately and efficiently. Due to the steep pressure head or steep water volumetric content gradients, highly nonlinear soil hydraulic properties and the rapid movement of the wetting front, accurate solutions for infiltration into a dry soil are usually difficult to obtain. Additionally, such problems often require very small time steps and large computation times. As an enhancement to the used ODE/MOL approach, Higher Order Finite Differencing, Varying Order Finite Differencing, Vertical Scaling, Adaptive Schemes and Non-uniform Stretching Techniques have been implemented and tested in this thesis. Success has been found in the ability of Vertical Scaling to simulate very steep moving front solution for the Burgers’ equation. Unfortunately, the results also show that Vertical Scaling needs significant research and improvement before their full potential in routine applications for difficult nonlinear problems, such as Richard’s equation with very steep moving front solution, can be realized. However, we have also shown that the use of the composed form of RE and a 2nd order finite differencing for the first order derivative approximation is conducive for modelling steep moving front problem in a very dry soil. Additionally, with the combination of an optimal influx value at the edges of the inlet, the ODE/MOL approach is able to model a 2-D infiltration in very dry soils, effectively and accurately. Furthermore, one of the strengths of this thesis is the use of a MATLAB PDE template. Implementing the ODE/MOL approach via a MATLAB PDE template has shown to be most suitable for modelling of partial differential equations. The plug and play mode of modifying the PDE template for solving time-dependent partial differential equations is user-friendly and easy, as compared to more conventional approaches using Pascal, Fortran, C or C++. The template offers greater modularity, flexibility, versatility, and efficiency for solving PDE problems in both 1-D and 2-D spatial dimensions. Moreover, the 2-D PDE template has been extended for irregular shaped domains.

The effects of irrigation-induced salinity and/or sodicity on sugarcane yield, and two growth parameters, namely stalk height and number of nodes per stalk , were investigated on a sugarcane estate in the Zimbabwean lowveld. The effects of soil salinity and/or sodicity on the size, activity and metabolic efficiency of the soil microbial community was also studied. Furrow-irrigated fields which had a gradient in soil salinity and/or sodicity which increased from the upper to lower ends of the fields were selected for this study. This gradient was recognized by decreasing sugarcane growth down from the upper to the lower ends and the appearance of salt on the soil surface at the lower ends of fields. Sugarcane growth was classified as either dead, poor, satisfactory or good; and soil samples (0-0 .15 m, 0.15-0 .3 m, 0.3-0 .6 m and 0.6-0.9 m) were taken from each of these areas. Soils from under adjacent areas of undisturbed veld were also sampled. Sugarcane growth and yields in micro-plots of the various areas of the fields were measured. Foliar samples of sugarcane were taken at 22 weeks of age and analysed for nutrient content. Soil salinity and sodicity were quantified by measuring pH(water), electrical conductivity (ECe) and cation content of saturation paste extracts and the exchangeable cation content. From this information, the sodium adsorption ratio (SARe)and exchangeable sodium percentage (ESP) were also calculated. The calcareous, vertic soils in the study area under undisturbed veld were found to have high pH values (8 to 9.5), very high exchangeable Ca and Mg concentrations and there was evidence of accumulation of soluble salts in the surface 0.15 m. Under sugarcane production, irrigation induced salinity and sodicity had developed. Under poor and dead sugarcane, high values for ECe, SARe, and ESP were generally encountered in the surface 0-0 .3 m of the profile. In addition, the pH values under sugarcane were often between 9 and 10 particularly in profiles where sugarcane grew poorly or had died. As expected, pH was positively related to ESP and SARe, but negatively related to ECe. Measurements of aggregate stability by wet sieving, the Emerson dispersion test and the Loveday dispersion score all showed that soils from the study sited tended to disperse and that dispersion was most apparent where high ESP and SARe values occurred in association with elevated pH values and relatively low ECe values. These measurements confirmed observations at the sites of low infiltration rates and restricted drainage particularly on the lower ends of fields where sugarcane had died. In addition to the above measurements it was also observed that there was a rise in the watertable under furrow irrigation and that the watertable was nearest to the surface at the lower ends of the fields. In some cases the watertable was observed to be only 0.2 to 0.3 m from the surface. Thus, death of roots due to anaerobic conditions could be occurring to a greater extent at the lower ends of the fields. Another consequence of the high watertable was that these vertic soils were observed to remain in a permanently swollen state. This limits air and water movement in the soil profile as such soils need to be allowed to dry out and crack regularly so that macroporosity can be restored. Sugarcane yield, stalk height and number of nodes per stalk were not significantly related to ECe. Sugarcane yields were, however, significantly correlated with ESP and pH while stalk height and number of nodes were negatively correlated with ESP, SARe and pH. These results suggested that sodicity was a more limiting factor for sugarcane growth than salinity. Foliar analysis of leaf tissue did not reveal substantial differences in macro- or micro-nutrient content between good and poorly-growing sugarcane. It was concluded that the gradient of decreasing sugarcane growth down the furrow-irrigated fields, with crop death at the lower ends, was the result of a combination of factors. That is, the watertable had risen due to over-irrigation and it was nearer the surface at the lower ends of the fields. Due to capillary rise of salts, this resulted in sodic and sometimes saline-sodic conditions in the surface soil. These conditions could limit plant growth through ion toxicities, plant water stress and inhibition of root growth and function and physiological processes. These would be induced by the high pH and high salt, Na and HC03- concentrations in soil solution. Poor physical conditions associated with sodicity and the continually swollen state of the soils presumably limited infiltration and aeration in the surface soil, and probably restricted root growth. In addition, it is likely that the high watertable limited effective crop rooting depth to about 0.2 m at the lower ends of the fields. The net result was that sugarcane died at the lower ends. A negative effect of soil salinity and/or sodicity was also observed on the soil microbial population. Significant negative correlations were obtained with ECe SARe and ESP with microbial biomass C and microbial activity (as measured by FDA hydrolytic activity or arginine ammonification rate). The activity of enzymes involved in C (P-glucosidase), P (phosphatase) and S (arylsulfatase) mineralization and potential nitrogen mineralization (as determined by aerobic incubation) were also negatively correlated with these factors, with the exception of arylsulfatase activity and ESP. All the above mentioned microbial population measures were also positively correlated with soil organic C content, besides potential nitrogen mineralization. The metabolic quotient, which provides an indication of stress and efficiency of the microbial community, increased considerably with increasing salinity and sodicity and decreased with soil organic C. Thus, increasing salinity and/or sodicity resulted in a smaller, more stressed, less efficient microbial community, while the turnover rate and cycling of C, N, P and S also decreased. It was concluded that salt affected soil not only causes a decline in sugarcane yield through raising the concentration of soluble salts in soil solution, but also has a detrimental effect on microbial activity and on mineralization of soil organic C, N, Sand P. / Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 2001.

A two year study was initiated in 2001 on a 2.4 ha site of mostly St. Amable loamy sand and shallow loamy sand at the Macdonald Campus Research Farm. This study sought to assess the effects of long term tillage and residue practices on soil physical properties and to relate these properties to their influence on total carbon, total nitrogen and soil microbial biomass-carbon. The site was set up as a factorial experiment with three tillage practices (no till---NT; reduced till---RT; and conventional till---CT) and two residue practices (with residue (grain corn), +R; without residue (silage corn), -R). Soil physical properties measured were bulk density, macroporosity at -6 kPa, saturated hydraulic conductivity (Ksat ), dry aggregate distribution, soil moisture and soil temperature. Wheel versus non-wheel track bulk density was also determined in the NT plots. Total porosity, soil water characteristic curves and pore volume distribution were derived from field samples. Crop yield was also assessed. Tillage alone had an effect on total porosity, bulk density, pore diameter and macroporosity. No individual physical property was significantly affected by the residue treatments; however, the tillage and residue interaction was significant for Ksat, soil moisture and soil temperature. Dry aggregate distribution was not affected by either tillage, residue or the combination of the two. Tillage affected total carbon and total nitrogen in the 0--0.10 m depth. Soil microbial biomass-carbon was affected by residue inputs. Total carbon and nitrogen were influenced by the bulk density, but none of the other soil physical properties. Soil microbial biomass-carbon was not influenced by any of the physical properties. Tillage and residue practices had no significant effect on crop yield for either year.