Revised; Originally published: 2009 / 6 pp. / Proper irrigation management requires that growers assess their irrigation needs by taking measurements of various physical parameters. Some use sophisticated equipment while others use tried and true common sense approaches. Whichever method used, each has merits and limitations. In developing any irrigation management strategy, two questions are common: “When do I irrigate?” and “How much do I apply?” This bulletin deals with the WHEN.

O presente trabalho teve por objetivo quantificar e caracterizar a variabilidade espacial e temporal da armazenagem de água no solo, do potencial mátrico, densidade de fluxo e evapotranspiração da água em um Latossolo Vermelho Amarelo Argissólico cultivado com citros. A parcela experimental constitui-se de duas transeções com 20 pontos de observação espaçados de 4,0 m, cada um deles localizado no centro da distância entre duas plantas ao longo da linha. A cultura de citros foi implantada em março de 1991 com espaçamento de 4,0 m entre plantas e 7,0 m entre linhas. Em cada ponto de observação foram instalados a) um tubo de acesso à uma sonda de nêutrons até a profundidade de 1,20 m, para a quantificação da armazenagem da água no solo, e b) três tensiômetros nas profundidades de 1,00 m, 1,10 m e 1,20 m para a quantificação do potencial mátrico e do gradiente de potencial total da água no solo. As medidas foram feitas ao longo de três anos. As medidas dos potenciais mátricos foram realizadas diariamente e as da armazenagem semanalmente. De cada ponto de observação e profundidade de 0,30 m, 0,50 m, 0,70 m, 0,90 m e 1,10 m foram coletadas amostras de solo com estrutura indeformada para a determinação da condutividade hidráulica saturada, da curva de retenção e a densidade do solo. Por meio da geoestatística, verificou-se uma dependência espacial para a armazenagem de água no solo com um alcance de 17,0 m em média e, para a densidade do solo, potencial mátrico e condutividade hidráulica saturada não se verificou estrutura de dependência espacial. A técnica da estabilidade temporal possibilita identificar no campo o ponto ou os pontos que, subestimam, superestimam ou representam a média de uma determinada variável. Pelo coeficiente de correlação de Spearman entre as datas, os valores de armazenagem e de potencial mátrico foram estáveis no tempo; para a armazenagem de água no solo, a correlação foi maior no período de recarga e, para o potencial mátrico, os coeficientes de correlação foram maiores para os períodos de secagem, ou seja, a estabilidade temporal foi maior para o os períodos de secagem. Por meio da diferença relativa foi possível identificar no estudo da estabilidade temporal, os pontos que mais se aproximaram da média que foram: o ponto 29 nos três anos, para a armazenagem de água no solo, pontos 24, 13 e 11 para o potencial mátrico da água no solo nos anos 1, 2 e 3, respectivamente. Por meio do balanço hídrico, verificou-se um consumo da água pela cultura de citros (evapotranspiração real) de 1.340 mm (consumo médio diário de 3,49 mm) e uma perda por drenagem interna que correspondeu a 10 %, em média nos três anos, da precipitação, para o solo e cultura em estudo. / The objective of the present work was to quantify and characterize spatial and temporal variability of water storage, matric potential, water flux density and actual evapotranspiration in an oxisol cropped to citrus. The experimental plot consisted of two transects with 20 observation points in a spacing of four meters. Each observation point was located in the central distance between two plants in the plant line. The citrus crop was installed in March of 1991 in a spacing of 4 x 7 m (four meters among plants in the line and seven meters among lines). In each observation point were installed a) one aluminiun tube to access a neutron probe till the depth of 1.2 m to determine water storage in the 0-1.2 m soil profile and b) three tensiometers at the depths of 1.0, 1.1 and 1.2 m to determine soil matric potential and soil water total potential gradient at the depth of 1.1 m then to calculated soil water flux density at the 1.1 m soil depth by means of Darcy-Buckingham equation. Measurements were made during three years, those of matric potential, dayly, and those of soil water content, weekly. In each observation point, undisturbed soil samples were removed from 0.3, 0.5, 0.7, 0.9 e 1.1 m soil depths to determine saturated soil hydraulic conductivity, soil water retention curve and soil bulk density. By means of geostatistical techniques, spatial dependence for soil water storage was verified with a range of 17 m in average. It was observed time stability for both soil water storage and matric potential that from the Spearman rank coefficients among dates. For the soil water storage, this coefficient showed higher values during the recharge period, that this, time stability for soil water storage was higher during the recharge period. For the matric potential occurred the inverse: time stability was higher during the drying period. By means of the relative difference from the mean, in the time stability study the following points closer were to the mean: point 29 (for the three years) for soil water storage and points 24, 13 and 11 for soil water matric potential for years 1, 2 and 3, respectively. By means of the soil water storage methodology, it was quantified a water consumption (actual evapotranspiration) for the citrus crop of 1,340 mm (daily average value of 3.49 mm) and a water loss by internal drainage that corresponded to 10 % in average, for the three years of experiment.

O presente trabalho teve por objetivo quantificar e caracterizar a variabilidade espacial e temporal da armazenagem de água no solo, do potencial mátrico, densidade de fluxo e evapotranspiração da água em um Latossolo Vermelho Amarelo Argissólico cultivado com citros. A parcela experimental constitui-se de duas transeções com 20 pontos de observação espaçados de 4,0 m, cada um deles localizado no centro da distância entre duas plantas ao longo da linha. A cultura de citros foi implantada em março de 1991 com espaçamento de 4,0 m entre plantas e 7,0 m entre linhas. Em cada ponto de observação foram instalados a) um tubo de acesso à uma sonda de nêutrons até a profundidade de 1,20 m, para a quantificação da armazenagem da água no solo, e b) três tensiômetros nas profundidades de 1,00 m, 1,10 m e 1,20 m para a quantificação do potencial mátrico e do gradiente de potencial total da água no solo. As medidas foram feitas ao longo de três anos. As medidas dos potenciais mátricos foram realizadas diariamente e as da armazenagem semanalmente. De cada ponto de observação e profundidade de 0,30 m, 0,50 m, 0,70 m, 0,90 m e 1,10 m foram coletadas amostras de solo com estrutura indeformada para a determinação da condutividade hidráulica saturada, da curva de retenção e a densidade do solo. Por meio da geoestatística, verificou-se uma dependência espacial para a armazenagem de água no solo com um alcance de 17,0 m em média e, para a densidade do solo, potencial mátrico e condutividade hidráulica saturada não se verificou estrutura de dependência espacial. A técnica da estabilidade temporal possibilita identificar no campo o ponto ou os pontos que, subestimam, superestimam ou representam a média de uma determinada variável. Pelo coeficiente de correlação de Spearman entre as datas, os valores de armazenagem e de potencial mátrico foram estáveis no tempo; para a armazenagem de água no solo, a correlação foi maior no período de recarga e, para o potencial mátrico, os coeficientes de correlação foram maiores para os períodos de secagem, ou seja, a estabilidade temporal foi maior para o os períodos de secagem. Por meio da diferença relativa foi possível identificar no estudo da estabilidade temporal, os pontos que mais se aproximaram da média que foram: o ponto 29 nos três anos, para a armazenagem de água no solo, pontos 24, 13 e 11 para o potencial mátrico da água no solo nos anos 1, 2 e 3, respectivamente. Por meio do balanço hídrico, verificou-se um consumo da água pela cultura de citros (evapotranspiração real) de 1.340 mm (consumo médio diário de 3,49 mm) e uma perda por drenagem interna que correspondeu a 10 %, em média nos três anos, da precipitação, para o solo e cultura em estudo. / The objective of the present work was to quantify and characterize spatial and temporal variability of water storage, matric potential, water flux density and actual evapotranspiration in an oxisol cropped to citrus. The experimental plot consisted of two transects with 20 observation points in a spacing of four meters. Each observation point was located in the central distance between two plants in the plant line. The citrus crop was installed in March of 1991 in a spacing of 4 x 7 m (four meters among plants in the line and seven meters among lines). In each observation point were installed a) one aluminiun tube to access a neutron probe till the depth of 1.2 m to determine water storage in the 0-1.2 m soil profile and b) three tensiometers at the depths of 1.0, 1.1 and 1.2 m to determine soil matric potential and soil water total potential gradient at the depth of 1.1 m then to calculated soil water flux density at the 1.1 m soil depth by means of Darcy-Buckingham equation. Measurements were made during three years, those of matric potential, dayly, and those of soil water content, weekly. In each observation point, undisturbed soil samples were removed from 0.3, 0.5, 0.7, 0.9 e 1.1 m soil depths to determine saturated soil hydraulic conductivity, soil water retention curve and soil bulk density. By means of geostatistical techniques, spatial dependence for soil water storage was verified with a range of 17 m in average. It was observed time stability for both soil water storage and matric potential that from the Spearman rank coefficients among dates. For the soil water storage, this coefficient showed higher values during the recharge period, that this, time stability for soil water storage was higher during the recharge period. For the matric potential occurred the inverse: time stability was higher during the drying period. By means of the relative difference from the mean, in the time stability study the following points closer were to the mean: point 29 (for the three years) for soil water storage and points 24, 13 and 11 for soil water matric potential for years 1, 2 and 3, respectively. By means of the soil water storage methodology, it was quantified a water consumption (actual evapotranspiration) for the citrus crop of 1,340 mm (daily average value of 3.49 mm) and a water loss by internal drainage that corresponded to 10 % in average, for the three years of experiment.

Submitted by (lucia.rodrigues@ufrpe.br) on 2016-07-05T11:23:22Z No. of bitstreams: 1 Edivan Rodrigues de Souza.pdf: 1105357 bytes, checksum: 872b1146ec684bad63978227ceff129f (MD5) / Made available in DSpace on 2016-07-05T11:23:22Z (GMT). No. of bitstreams: 1 Edivan Rodrigues de Souza.pdf: 1105357 bytes, checksum: 872b1146ec684bad63978227ceff129f (MD5) Previous issue date: 2007-02-26 / Conselho Nacional de Pesquisa e Desenvolvimento Científico e Tecnológico - CNPq / An experiment has been performed aiming to evaluate the spatial-time variation patterns of soil humidity in an irrigated area in Pesqueira – PE. The experiment has been carried out in an irrigated plot with carrot, with duration of 96 days. Two irrigated sectors (1 and 2) with 900 m2 each (30 m x 30 m) have been monitored in the experiment, using microsprinklers. Dead cover has been used to cover the soil surface after 23 days of sowing, in sector 2. The irrigation water was derived from a nearby Amazon well. The applied irrigation has been estimated considered the crop demand and a leaching fraction of 20%. Neutron probe access tubes have been installed to measure soil moisture at 20 and 40 cm depths, in 49 points in sector 1 and 52 points in sector 2, in a 5 x 5 m grid. The neutron probe readings were performed one hour after irrigation, twice a week, with a total of 20 monitoring days.Data has been analysed using descriptive statistics, geostatistics and temporal stability, based on relative difference and the Spearman correlation. The soil moisture in sector 2, for the two depths, was higher than in sector 1 for the whole cropping period. Temporal dependence for the whole period has been found through high values of the Spearman correlation test thoughout the sampling times. It has been possible to identify points in the sampling space representing the average soil moisture content, using the relative difference technique. The spatial dependence of the soil moisture content has been inferred through semi-variograms and contouring maps for the two sectors, at the two different depths. / Com o objetivo de avaliar o comportamento da umidade do solo, espacial e temporalmente, foi realizado um experimento em Pesqueira – PE, durante um cultivo de cenoura (Daucus carota L.) com duração de 96 dias. Dois setores de irrigação (1 e 2), cada um com 900 m2 (30 x 30 m) foram instalados, adotando um sistema de irrigação por microaspersão,utilizando água oriunda de poço Amazonas. Aos 23 dias após a semeadura foi adicionada cobertura morta no setor 2. O suprimento de água foi baseado na necessidade da cultura acrescida de uma fração de lixiviação de 20%. Foram instalados tubos de acesso para sonda de nêutrons para medição de umidade do solo, nas profundidades de 20 e 40 cm, em 49 pontos no setor 1, e 52 pontos no setor 2, em nós de uma malha de 5 x 5 m. As leituras com a sonda de nêutrons foram realizadas uma hora após o término da irrigação, com freqüência de duas vezes por semana, totalizando durante o ciclo da cultura 20 dias de monitoramento. Os dados foram avaliados adotando-se métodos de estatística descritiva, geoestatística e estabilidade temporal utilizando a diferença relativa e a correlação de Spearman. O setor 2, para as duas profundidades, apresentou umidade média maior que o setor 1 durante quase todo o ciclo da cultura. Os valores do teste de correlação de Spearman apresentaram-se altos entre as épocas de amostragens, indicando dependência temporal ao longo de todo o ciclo. Através da técnica da diferença relativa foi possível identificar pontos no espaço amostral que representam a média da umidade do solo. A dependência espacial da umidade foi inferida através dos semivariogramas e dos mapas de isolinhas para os dois setores em suas diferentes profundidades.

Improved soil water conservation has become an important subject in semi-arid areas due to low and erratic rainfall which is often combined with higher temperatures to provide unsuitable conditions for successful crop productivity. Dryland agriculture remains vulnerable to yield losses in these areas. This calls for implementation of conservation agricultural practices that would improve dryland maize productivity. An on-station field trial was started in 2007 at Zeekoegat experimental farm (24 kilometers north of Pretoria), to establish the effect of different conservation agriculture practices on soil and plant properties. The experimental lay-out was a split-plot randomized complete block design, replicated three times, with each replicate split into two tillage systems (whole plots) and then each whole plot (reduced tillage (RT) and conventional tillage (CT)) was subdivided into 12 treatments (two fertilizer levels x 6 cropping patterns). The present study explored the impacts of different tillage practices, cropping patterns and fertilization levels on soil water content, soil temperature and dryland maize productivity during the 2010/11 and 2011/12 growing seasons. To improve the quality of soil water content (SWC) data, the effect of correction for concretions on soil bulk density and the relationship between volumetric soil water content (SWC) vs neutron water meter (NWM) count ratios was also investigated. Corrections for concretions on soil bulk density did not improve NWM calibrations in this study. In all seasons, significantly higher mean SWC was found under RT treatment than in CT at all depths except at 0-300 mm. For example, during the 2010/11 growing season, SWC under RT was 1.32 % and 1.10 % higher than CT for the 300 – 1350 mm and 0 – 1350 mm soil profiles, respectively. The mean weekly SWC was consistently higher for RT throughout both the growing seasons. Significantly higher SWC was also found under monoculture at all soil depths (except at 0-300 mm during 2011/12) compared to treatments under intercropping. For example, during 2010/11, at 0-300mm, SWC under maize monoculture was 1.72 % higher than under intercropping. The maximum and minimum soil temperatures were significantly higher at 100 and 400 mm soil depths under CT than under RT during 2010/11. During 2011/12, significantly higher minimum soil temperatures at 100 mm depth and lower temperature differences (maximum – minimum soil temperatures) at 400 mm depth were observed under intercropping. Despite the higher SWC and reduced soil temperature under RT, the maize seeds emergence rate was lower and plant stand was reduced. This is attributed to other factors associated with RT systems such as increased soil penetration resistance which often leads to poor root development. The lower soil temperatures under RT were generally within the range that would not be expected to inhibit growth and uptake of nutrients. Slower growth under RT resulted in lower biomass and grain yield. Plants that received high fertilizer rates grew more vigorously than plants under lower fertilizer levels when water was not a limiting factor, but produced lower grain yield due to water shortage in March, especially in 2011/12. The harvest index was therefore lower for treatments that received high fertilizer levels. Maize biomass under monoculture x low fertilizer level was significantly lower compared to other fertilizer x cropping pattern treatments. Maize plant growth under intercropping was improved throughout the seasons, which led to significantly higher grain yield than under maize monoculture. It is therefore recommended that farmers in dryland areas take the advantage of intercropping maize with legumes to obtain higher maize productivity. Further research should focus on investigating the possibility of roots restrictions occurring under RT conditions and under various environmental and soil conditions. / Dissertation (MScAgric)--University of Pretoria, 2014. / lk2014 / Plant Production and Soil Science / MScAgric / Unrestricted

]The scale difference between point in situ soil moisture measurements and low resolution satellite products limits the quality of any validation efforts in heterogeneous regions. Cosmic Ray Neutron Probes (CRNP) could be an option to fill the scale gap between both systems, as they provide area-average soil moisture within a 150-250 m radius footprint. In this study, we evaluate differences and similarities between CRNP observations, and surface soil moisture products from the Advanced Microwave Scanning Radiometer 2 (AMSR2), the METOP-A/B Advanced Scatterometer (ASCAT), the Soil Moisture Active and Passive (SMAP), the Soil Moisture and Ocean Salinity (SMOS), as well as simulations from the Global Land Data Assimilation System Version 2 (GLDAS2). Six CRNPs located on five continents have been selected as test sites: the Rur catchment in Germany, the COSMOS sites in Arizona and California (USA), and Kenya, one CosmOz site in New SouthWales (Australia), and a site in Karnataka (India). Standard validation scores as well as the Triple Collocation (TC) method identified SMAP to provide a high accuracy soil moisture product with low noise or uncertainties as compared to CRNPs. The potential of CRNPs for satellite soil moisture validation has been proven; however, biomass correction methods should be implemented to improve its application in regions with large vegetation dynamics.

O objetivo do presente trabalho foi estudar a variabilidade espacial dos parâmetros da equação da condutividade hidráulica determinada no campo em função do conteúdo de água no solo, pelo método do perfil instantâneo, e avaliar a estabilidade temporal da armazenagem da água no solo, com vistas a identificação de um local de amostragem ótimo para a determinação da densidade de fluxo da água pela equação de Darcy-Buckingham. O estudo foi desenvolvido num Latossolo Vermelho Amarelo, textura areno-argiloso, em área experimental do Campus "Luiz de Queiroz", Universidade de São Paulo, município de Piracicaba, Estado de São Paulo, Brasil. Suas coordenadas geográficas são: 22° 42’ 43,3’’ de latitude sul, 47° 37’ 10,4’’ de longitude oeste e 456 m de altitude. A parcela experimental apresentava um comprimento de 45 m e uma largura de 15 m, na qual foram instalados 40 tubos de alumínio para acesso de uma sonda de nêutrons para medida do conteúdo da água no solo nas profundidades 0,20 m; 0,40 m; 0,60 m; 0,80 m e 1,00 m e cálculo da armazenagem da água no perfil 0- 1,0 m. A distribuição desses tubos foi feita na forma de uma grade de quatro colunas por dez linhas, com cada tubo distando de seu vizinho de 5 m. As funções K(θ) nos 40 pontos foram determinadas a partir das análises de regressão de θ em função de lnt e hz em função de lnt, durante o processo de redistribuição da água no solo. De posse das 40 funções K(θ) nas cinco profundidades estudadas, foram aplicadas as técnicas geoestatitisticas para o estudo da variabilidade espacial dos parâmetros θ0, K0 e γ da função. Foi realizada também a análise da estabilidade temporal da armazenagem da água no solo, ao longo do período de redistribuição da água no solo para verificar quais e quantos são os locais adequados para o monitoramento da água precisão aceitável e reduzido esforço amostral. Pelos resultados obtidos, pôde-se concluir que: a) os métodos geoestatísticos utilizados foram adequados para descrever a estrutura de dependência espacial dos parâmetros da relação da condutividade hidráulica em função da umidade do solo: θ0 , K0 e γ; b) para as três variáveis estudadas ( θ0 , K0 e γ) houve estrutura de dependência espacial dos parâmetros na escala utilizada com alcances máximos de 8,33, 19,09 e 10,35 m; c) a técnica da estabilidade temporal que possibilita identificar, no campo, o ponto, ou os pontos, que representam a média e os pontos que superestimam ou subestimam a média real de determinada variável, identificou, para os valores de armazenagem da água no solo do presente estudo, os pontos 19, 20 e 21 como os mais representativos da média geral do campo; d) a metodologia com base nos coeficientes de correlação de Spearman também permitiu concluir que os valores de armazenagem da água no solo, foram estáveis no tempo, para os 40 pontos amostrados. Palavras-chave: perfil instantâneo, estabilidade temporal, sonda de nêutrons, armazenagem / The objective of this work was to study the spatial variability of the parameters of the hydraulic conductivity equation determined in the field as a function of soil water content, by the instantaneous profile method, and to evaluate the soil water storage time stability, in order to identify a sampling location for the determination of soil water flux by means of Darcy-Buckingham equation. The study was carried out in a clay sandy Oxisol in the country of Piracicaba, State of São Paulo, Brazil (22º42’ 43,3’’ S, 47° 37’ 10,4’’ W, 546 m). The dimensions of the experimental plot were 45 m x 15 m in wich 40 aluminium tubes were installed to acess a neutron probe to measure the soil water content at the depths of 0.2, 0.4, 0.6, 0.8 and 1.0 m and, then, calculate the soil water storage of the 0 - 1.0 m soil layer. The distribution of these tubes were made in grid of four columns by ten lines in spacing of 5m x 5m. The Kθ functions were determined in the 40 points from regression analyses of θ as function lnt and hz as a function of lnt, being K the hydraulic conductivity, θ the volumetric soil water content, z h the soil water storage in the 0 - Z m layer and t the soil water redistribution time. With the 40 Kθ functions in the five studied soil depths, geostatistical techniques were used to evaluate the spatial variability of the parameters 0 θ , 0 K and γ of the function ( ) [ ] 0 0 exp θ θ γ − = K K , where the subindex o means lnt = 0. Soil water storage time stability analysis were also carried out along the soil water redistribution period in order to verify which and how many are the adequate locations for water monitoring with acceptable precisi on and reduced sample effort. From the results, the follwing could conclude: (i) the used geostatistical methods were adequate to described the spatial dependence structure of the parameters θ0 , Kθ0 and γ; (ii) there were a spatial dependence structure of the parameters in the used scale with maximum ranges of 8.33, 19.09 and 10.35 m; (iii) from the time stability technique, it was possible to identify the points 19,20 and 21 as the more representative of the field overall mean; (iv) the rank Spearmam coefficients also showed that the soil water storage of the 40 sampled points were in the time.

O objetivo do presente trabalho foi estudar a variabilidade espacial dos parâmetros da equação da condutividade hidráulica determinada no campo em função do conteúdo de água no solo, pelo método do perfil instantâneo, e avaliar a estabilidade temporal da armazenagem da água no solo, com vistas a identificação de um local de amostragem ótimo para a determinação da densidade de fluxo da água pela equação de Darcy-Buckingham. O estudo foi desenvolvido num Latossolo Vermelho Amarelo, textura areno-argiloso, em área experimental do Campus "Luiz de Queiroz", Universidade de São Paulo, município de Piracicaba, Estado de São Paulo, Brasil. Suas coordenadas geográficas são: 22° 42’ 43,3’’ de latitude sul, 47° 37’ 10,4’’ de longitude oeste e 456 m de altitude. A parcela experimental apresentava um comprimento de 45 m e uma largura de 15 m, na qual foram instalados 40 tubos de alumínio para acesso de uma sonda de nêutrons para medida do conteúdo da água no solo nas profundidades 0,20 m; 0,40 m; 0,60 m; 0,80 m e 1,00 m e cálculo da armazenagem da água no perfil 0- 1,0 m. A distribuição desses tubos foi feita na forma de uma grade de quatro colunas por dez linhas, com cada tubo distando de seu vizinho de 5 m. As funções K(θ) nos 40 pontos foram determinadas a partir das análises de regressão de θ em função de lnt e hz em função de lnt, durante o processo de redistribuição da água no solo. De posse das 40 funções K(θ) nas cinco profundidades estudadas, foram aplicadas as técnicas geoestatitisticas para o estudo da variabilidade espacial dos parâmetros θ0, K0 e γ da função. Foi realizada também a análise da estabilidade temporal da armazenagem da água no solo, ao longo do período de redistribuição da água no solo para verificar quais e quantos são os locais adequados para o monitoramento da água precisão aceitável e reduzido esforço amostral. Pelos resultados obtidos, pôde-se concluir que: a) os métodos geoestatísticos utilizados foram adequados para descrever a estrutura de dependência espacial dos parâmetros da relação da condutividade hidráulica em função da umidade do solo: θ0 , K0 e γ; b) para as três variáveis estudadas ( θ0 , K0 e γ) houve estrutura de dependência espacial dos parâmetros na escala utilizada com alcances máximos de 8,33, 19,09 e 10,35 m; c) a técnica da estabilidade temporal que possibilita identificar, no campo, o ponto, ou os pontos, que representam a média e os pontos que superestimam ou subestimam a média real de determinada variável, identificou, para os valores de armazenagem da água no solo do presente estudo, os pontos 19, 20 e 21 como os mais representativos da média geral do campo; d) a metodologia com base nos coeficientes de correlação de Spearman também permitiu concluir que os valores de armazenagem da água no solo, foram estáveis no tempo, para os 40 pontos amostrados. Palavras-chave: perfil instantâneo, estabilidade temporal, sonda de nêutrons, armazenagem / The objective of this work was to study the spatial variability of the parameters of the hydraulic conductivity equation determined in the field as a function of soil water content, by the instantaneous profile method, and to evaluate the soil water storage time stability, in order to identify a sampling location for the determination of soil water flux by means of Darcy-Buckingham equation. The study was carried out in a clay sandy Oxisol in the country of Piracicaba, State of São Paulo, Brazil (22º42’ 43,3’’ S, 47° 37’ 10,4’’ W, 546 m). The dimensions of the experimental plot were 45 m x 15 m in wich 40 aluminium tubes were installed to acess a neutron probe to measure the soil water content at the depths of 0.2, 0.4, 0.6, 0.8 and 1.0 m and, then, calculate the soil water storage of the 0 - 1.0 m soil layer. The distribution of these tubes were made in grid of four columns by ten lines in spacing of 5m x 5m. The Kθ functions were determined in the 40 points from regression analyses of θ as function lnt and hz as a function of lnt, being K the hydraulic conductivity, θ the volumetric soil water content, z h the soil water storage in the 0 - Z m layer and t the soil water redistribution time. With the 40 Kθ functions in the five studied soil depths, geostatistical techniques were used to evaluate the spatial variability of the parameters 0 θ , 0 K and γ of the function ( ) [ ] 0 0 exp θ θ γ − = K K , where the subindex o means lnt = 0. Soil water storage time stability analysis were also carried out along the soil water redistribution period in order to verify which and how many are the adequate locations for water monitoring with acceptable precisi on and reduced sample effort. From the results, the follwing could conclude: (i) the used geostatistical methods were adequate to described the spatial dependence structure of the parameters θ0 , Kθ0 and γ; (ii) there were a spatial dependence structure of the parameters in the used scale with maximum ranges of 8.33, 19.09 and 10.35 m; (iii) from the time stability technique, it was possible to identify the points 19,20 and 21 as the more representative of the field overall mean; (iv) the rank Spearmam coefficients also showed that the soil water storage of the 40 sampled points were in the time.

Traditional irrigation was practiced in Ethiopia since time immemorial. Despite this, water productivity in the sector remained low. A survey on the Godino irrigation scheme revealed that farmers used the same amount of water and intervals, regardless of crop species and growth stage. In an effort to improve the water productivity, two traditional irrigation scheduling methods were compared with two scientific methods, using furrow irrigation. The growth performance and tuber yield of potato (cv. Awash) revealed that irrigation scheduling using a neutron probe significantly outperformed the traditional methods, followed by the SWB model Irrigation Calendar. Since the NP method involves high initial cost and skills, the use of the SWB Calendar is suggested as replacement for the traditional methods. SWB is a generic crop growth model that requires parameters specific to each crop, to be determined experimentally before it could be used for irrigation scheduling. It also accurately describes deficit irrigation strategies where water supply is limited. Field trials to evaluate four potato cultivars for growth performance and assimilate partitioning, and onions' critical growth stages to water stress were conducted. Crop-specific parameters were also generated. Potato and onion crops are widely grown at the Godino scheme where water scarcity is a major constraint. These crop-specific parameters were used to calibrate and evaluate SWB model simulations. Results revealed that SWB model simulations for Top dry matter (TDM), Harvestable dry matter (HDM), Leaf area index (LAI), soil water deficit (SWD) and Fractional interception (FI) fitted well with measured data, with a high degree of statistical accuracy. The response of onions to water stress showed that bulb development (70-110 DATP) and bulb maturity (110-145) stages were most critical to water stress, which resulted in a significant reduction in onion growth and bulb yields. SWB also showed that onion yield was most sensitive to water stress during these two stages. An irrigation calendar, using the SWB model, was developed for five different schemes in Ethiopia, using long-term weather data and crop-specific parameters for potatoes and onions. The calendars revealed that water depth varied, depending on climate, crop type and growth stage. / Thesis (PhD)--University of Pretoria, 2009. / Plant Production and Soil Science / unrestricted

The vadose zone is the unsaturated zone between the ground surface and water table. This zone is of much importance as it acts as a link between surface water and ground water. Knowledge of soil moisture in this zone is very much essential to understand the meteorologic, hydrologic and agronomic process. Flow and transport in the unsaturated zone are more complex compared to saturated medium, as the pores in unsaturated zone are partly filled by air and partly by water. Most of vadose zone studies are done on agricultural plots where anthropogenic activities govern the vadose zone flows. Vadose zone studies in natural pristine conditions such as in forested areas where no anthropogenic activities are present are very limited that too in Indian conditions are rare. The present research work deals with understanding of the flow behavior in the vadose zone in a small experimental forested watershed called Mule Hole. Mule Hole watershed is 4.5 km2 and located in Bandipur National Park in Chamrajnagar District of Karnataka state, in the southern part of India. The forest is of deciduous type with 3 to 4 months of leafless dry period. The watershed has mean annual 25 years rainfall of 1120 mm and mean yearly temperature is 27o. The rainfall pattern is bimodal i.e. it receives rainfall during South West Monsoon (June -September) and North East Monsoon (October – December) with dominant rainfall occurring during South West Monsoon. Human activity is minimal as watershed is a part of Bandipur National Park, dedicated to wildlife and biodiversity preservation. The watershed consists of around 80 % of red soils, and black soil and saprolite covering the rest. The first part of the study involves soil moisture measurements by neutron probe and electrical resistivity measurements by geophysical method and their linking, i.e. developing volumetric soil moisture vs electrical resistivity relationship. The second part of the study involves application of neutron probe soil moisture measurement in identifying relationship between soil and erosion in the watershed. The third part involves development of two dimensional (2D) vadose zone model for watershed and validating it with measured data. The last part involves development of three dimensional model of watershed and validating it with observed data. Vadose zone is briefly described in chapter 1 along with its governing equations. Different soil moisture measurement techniques including invasive and non – invasive ones are also discussed. Different vadose zone modeling software which are public domain as well as commercial ones are also discussed. The chapter ends with organization of this thesis. Chapter 2 reviews relevant literature related to this study with focus on soil moisture measurement techniques and vadose zone flow modeling. Different soil moisture measurement techniques, their applications and limitations are reviewed. In the soil moisture measurement techniques, invasive and non – invasive types are reviewed. In the modeling part, different vadose zone models for 2D and 3D flow along with its applications and limitations are reviewed. Also a brief review about application of HYDRUS 2D/3D model is done which is used for the vadose zone modeling in this thesis. Chapter 3 introduces study area Mule Hole watershed, which is a forested watershed located in Bandipur National Park, Karnataka. India. The watershed has mean annual 25 years rainfall of 1120 mm and mean yearly temperature is 27o. The watershed has average regolith thickness or vadose zone of 17 m with roots of the trees able to penetrate up to groundwater. A toposequence T1 is identified in the watershed which has red soil – black soil confluence where soil moisture measurements and electrical resistivity measurements are carried out. The toposequence consists of 8 layers with organic layer forming the top layer followed by 3 red soil layer with 2 black soil layers intruding from stream into red soil layers and sandy weathered horizon at base of red and black soil. Also a sandy horizon at the top of black soil. Soil moisture measurements with neutron probe and electrical resistivity measurements with electrical logging tool which are done on toposequence periodically for two years are explained and the data are presented in this chapter. These data are used for validation of vadose zone models. Chapter 4 discusses in detail about comparison of electrical resistivity by geophysical method and neutron probe logging for soil moisture monitoring in a forested watershed. The electrical resistivity data and soil moisture data are compared for different soils and existence of relationship between them are studied and discussed in this chapter. For the red soil, existence of relationship between volumetric soil moisture content and electrical resistivity is found. Chapter 5 discusses soil moisture measurements as a tool to study erosion processes in forested watershed. Hydrodynamic behavior of the red soil – black soil system at toposequence T1 is studied using neutron probe soil moisture measurements. Two distinctive types of erosional landforms have been identified at T1 viz, rotational slips (Type 1); seepage erosion (Type 2),which are highlighted by neutron probe soil moisture measurements. Based on the observations relative chronology of formulation of different soil horizons are studied, which guided in developing four-stage model showing the relative chronology in the recent formation of the soil cover at downslope. Chapter 6 discusses application of 2D vadose zone modeling using HYDRUS – 2D model at two experimental sites in forested watershed where soil moisture monitoring and groundwater monitoring have been conducted. At the first site, which is toposequence T1 in the forested watershed, where soil moisture measurements are done, three case studies for comparison of daily scale data with hourly scale data and effects of internal layering by clubbing red soil layers and black soil layers to equivalent red soil and black soil layers respectively are performed. The model is run for two years. In that, first year results are used for calibrating the model where measured soil moisture content data are used to get soil hydraulic parameters for all the three cases by inverse modeling using Marquardt – Levenberg algorithm which is a part of HYDRUS 2D. The parameters thus obtained fall under particular soil range and performed efficiently in predicting soil moisture content. The second year results of model run is used for validation of the model in all the three cases where simulated soil moisture content is compared with measured soil moisture content. It is found that model is performing well and match between measured and simulated soil moisture contents is good in all the three cases. It can be said that having hourly scale data with detailed layering information is always advantageous in modeling soil moisture content. But, in absence of hourly scale data or finer scale data and absence of detailed layering information, the soil moisture model can also perform well. The scale of data and detailed layering information has minimal effect on soil moisture modeling. At the second site ERT profile near the watershed outlet has five monitoring wells are available and all layering information regarding regolith and hard rock layer distribution profiles. The soil hydraulic parameters obtained at toposequence T1 for soil and sandy weathered horizon are used and tested at this site to simulate the groundwater levels. The parameter for rock layer is estimated by testing different hydraulic parameters from HYDRUS database. The results are validated using observed groundwater levels at the site. The results show significant match between observed and simulated groundwater levels. Chapter 7 discusses 3D modeling of Mule Hole forested watershed using HYDRUS – 3D model. A three layer model of Mule Hole along with its topographic details is modeled. The layering information is derived from geophysical study done at 12 Electrical Resistivity Tomography (ERT) profiles distributed in the watershed. The three layers considered are top soil layer followed by sandy weathered layer and bottom rock layer. Anisotropy in hydraulic conductivity, root water uptake and sloping water table are introduced to make the model more realistic. Soil hydraulic parameters obtained during 2D vadose zone modeling of toposequence T1 are used initially for soil and sandy weathered layers and are subsequently tuned to make model more efficient. Different scenarios are considered to test flux as well as constant head boundary conditions and effect of different porosities for rock layer. The model is run for 7 years and model simulations are validated with observed groundwater levels from monitoring wells across the watershed. The result shows good fit between simulated and observed groundwater levels especially for monitoring well which has shallow groundwater level. It is found that porosity in the rock layer is not uniform and there exist different porosities for the rock layer across the watershed. Also the distribution of sandy weathered zone requires improvement. The model is also able to predict ET closer to ET predicted by COMFORT model which was developed earlier. Also the model shows rise in groundwater fluxes as groundwater starts replenishing. Over all, the 3D model of Mule Hole watershed in HYDRUS – 3D worked well with satisfactory results and HYDRUS – 3D can be used for modeling small forested watersheds. Chapter 8 concludes the study and discusses the further scope of the work.