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Diss. (sammanfattning) Uppsala : Sveriges lantbruksuniversitet, 2009. / Härtill 4 uppsatser.

Diss. (sammanfattning). Uppsala : Sveriges lantbruksuniv. / Härtill 3 uppsatser.

Diss. (sammanfattning) Uppsala : Sveriges lantbruksuniv., 2009. / Härtill 4 uppsatser.

Diss. (sammanfattning) Uppsala : Sveriges lantbruksuniv. / Härtill 3 uppsatser.

From the Proceedings of the 1971 Meetings of the Arizona Section - American Water Resources Assn. and the Hydrology Section - Arizona Academy of Science - April 22-23, 1971, Tempe, Arizona / A study was made to determine how the evaporation rate from a bare Adelanto loam soil in Phoenix changes with season and with time since the last irrigation. The evaporation rates were determined by precision lysimeters in a bare field, with measurements being taken in every month of the year for at least a week after irrigation. The data exhibited a cosine-shaped curve, with a maximum evaporation rate of about 5 mm/day in summer and a minimum rate of about 2 mm/day in winter. By the seventh day, seasonal effects virtually disappear, and the evaporation rate is the same in both summer and winter, being about 2 mm/day after the 7th day and about 0.75 mm/day after the 21st day. It is generally accepted that soil dries in 3 stages, and the transition between the 1st and 2nd stages occurs when atmospheric conditions are no longer critical. In previous laboratory studies of soil drying, with constant atmospheric conditions, stage 1 was easily distinguished from stage II, and these results correlated closely with the equations of Gardner and Hillel. The individual drying curves of this field study were qualitatively different from the laboratory studies and did not confirm the predictions of the equations, suggesting that diurnal variations in temperature and other meteorological parameters have caused the difference.

From the Proceedings of the 1977 Meetings of the Arizona Section - American Water Resources Assn. and the Hydrology Section - Arizona Academy of Science - April 15-16, 1977, Las Vegas, Nevada / Soil water content was measured every two weeks during 1974-1975, using a neutron probe, at selected locations around the desert plant species creosote (Larria divaricata), bursage (Ambrosia deltoidea), and in an open space. The purpose of taking the measurements was to enable one to estimate the evapotranspiration rate of the desert plants by measuring soil moisture depletion. The sampling problem associated with measuring soil moisture, using neutron access tubes, is the number, location, and installation depth of the tubes. Analyses of the total soil moisture beneath the creosote plant showed greater variability between access tubes located near different plants the same distance from the crown of the plant than between tubes located around the same plant. Because of the size of the bursage plant, the variability in total soil moisture beneath the plant was greater among tubes around the same plant than between tubes at the same location at different plants.

From the Proceedings of the 1978 Meetings of the Arizona Section - American Water Resources Assn. and the Hydrology Section - Arizona Academy of Science - April 14-15, 1978, Flagstaff, Arizona / The equations of Darcy, Kostiakov, Ostashev, Philip, and four modified Philip equations were evaluated for use in predicting and controlling rainwater infiltration and rainfall excess in crop and rangelands. These eight equations were least- square fitted to data from ring, border-irrigation, closed-top, and sprinkling infiltrometers. Kostiakov's equation satisfied the evaluation criteria better than the other seven equations. The parameters of Kostiakov's equation were physically interpreted by relating their magnitudes to some physical, biological, and hydraulic characteristics of the infiltration system. These characteristics included several infiltration abatement and augmentation processes and factors that are controlled at the soil surface by land management practices. The eight equations were also fitted to rainfall data to permit calculating runoff from small surface areas about the size of a typical crop plant. Comparison of the regression curves for infiltration and rainfall suggested that land management practices that appropriately alter the soil surface will permit wide-range control of infiltration, runoff, and erosion; and thereby achieve conservation and more efficient use of soil and water resources for crop production. The most important soil surface conditions affecting infiltration were microroughness, macroporosity, plant litter, and effective surface head.

From the Proceedings of the 1978 Meetings of the Arizona Section - American Water Resources Assn. and the Hydrology Section - Arizona Academy of Science - April 14-15, 1978, Flagstaff, Arizona / Described is a microroughness meter developed to obtain numerous and accurate measurements of rangeland surface microroughness and characteristics. The meter, which consists of four basic parts: (1) meter base and pin guide, (2) pin lifting support bar and lifting mechanism, (3) 100 vertically moving pins, and (4) stripchart support guide and winding mechanism, was designed to measure soil surface evaluations and characteristics of a 1m2 plot. Performance tests on multi-plot sprinkler infiltrometer studies conducted on the Santa Rita Experimental Range in southeastern Arizona indicated that the meter was accurate and relatively precise in repeating soil surface roughness measurements but was not precise in defining the theoretical characteristics of constructed surfaces. It was concluded, however, that these errors in precision were insignificant and due partly to surface geometry construction errors and that the meter is a convenient, quick, simple and accurate means of measuring surface roughness in studies requiring many plots and data points.

Made available in DSpace on 2016-08-31T13:24:20Z (GMT). No. of bitstreams: 1 LuizAAS_DISSERT.pdf: 2790394 bytes, checksum: 1bac58cbcfc89d893d66e58cfa50081f (MD5) Previous issue date: 2009-03-06 / In this work, a mathematical model was developed for the simulation of soil water movement under surface drip irrigation, being used the method of the finite volumes for the resolution of the partial differential equation of water flow in porous media. The soil water flow was treated three-dimensionally for the determination of your movement in the infiltration and redistribution phases. The model allows the determination dimensions and shape of the wetted bulb, of the partial and final dimension of the saturated disc radius and the determination of the saturated soil volume, when to deal about of isolated bulb. In the case of overlapping bulbs, the model allows the determination of the width and depth of the formed wetted strip, making possible the choice of the drippers spacing that better it is adapted to the conditions of the irrigation project and management. A computational program was developed with base in the model, and the obtained results were validated starting from comparisons with field data and results of simulations of other models. These comparisons demonstrated that the model presents reliable results and it can be used as tool for the designing of drip irrigation installations. The sensibility analysis accomplished starting from the variation of some parameters of the soil and of the emitter (initial moisture, saturated soil hydraulic conductivity and trickle discharge), it demonstrated that, with relationship to the final moisture inside of the bulb, the model is so much relatively sensitive to positive variations as negatives of those parameters. / Neste trabalho, foi desenvolvido um modelo matemático para a simulação do movimento de água no solo sob irrigação por gotejamento superficial, utilizando-se o método dos volumes finitos para a resolução da equação diferencial parcial de escoamento de água em meios porosos. O fluxo de água no solo foi tratado tridimensionalmente para a determinação do seu movimento nas fases de infiltração e redistribuição. O modelo permite a determinação da forma e das dimensões do bulbo molhado, da dimensão parcial e final do raio do disco saturado e a determinação do volume de solo saturado, quando tratar-se de bulbo isolado. No caso de bulbos sobrepostos, o modelo permite a determinação da largura e profundidade da faixa molhada formada, possibilitando a escolha do espaçamento entre gotejadores que melhor se adeque às condições do projeto e manejo da irrigação. Um programa computacional foi desenvolvido com base no modelo, e os resultados obtidos foram validados a partir de comparações com dados de campo e resultados de simulações de outros modelos. Estas comparações demonstraram que o modelo apresenta resultados confiáveis e pode ser utilizado como ferramenta para o dimensionamento de instalações de irrigação por gotejamento. A análise de sensibilidade realizada a partir da variação de alguns parâmetros do solo e do emissor (umidade inicial, condutividade hidráulica do solo saturado e vazão do gotejador), demonstrou que, com relação à umidade final dentro do bulbo, o modelo é relativamente sensível tanto à variações positivas quanto negativas desses parâmetros.