Water Transfer from Soil to the Atmosphere as Related to Climate and Soil Properties

Facilities and Systems - Design of the lysimetric facility of the project began in 1966. During 1967, soil cores were taken for the lysimeters, and in 1968 an unforseen temperature problem in the lysimeters was solved. A total of 9 undisturbed soil cores were made into lysimeters. Since cores were procured, the lysimeters have the "natural" soil properties. Such lysimeters will be valuable tools for further studies. The lysimeters were designed for either visual or recorded readout of data. Initially, plans were made to use a datalogger owned by the USWB to collect the data. However, it is not reliable, and a system of strip chart recorders had to be procured to record the data. This proved to be time consuming, and subjected the data to possible human error when it was reduced to numerical form from the strip charts. Research-Results - Either the combination method of van Bavel or the Bowen Ratio will provide a fair estimate of evaporation from a wet soil surface in the area. In general, the combination method tends to overestimate while the Bowen Ratio tends to underestimate evaporation. This is due to the fact that the combination method places a strong emphasis on this parameter. Average wind speeds in the area commonly exceed 4 m/sec. Conductivity Studies - The conductivity of the Olton loam soil is very low at fairly low soil water pressures corresponding to high contents. This is an asset in preventing evaporation losses, but may be detrimental to crop production in that the crops need to develop extensive root systems to use the stored soil moisture. Canopy Effects on Evaporation - Evaporation within a cotton crop canopy following rains is related to the net radiation reaching the soil surface. After the surface dries, the moisture content of the soil surface is the limiting parameter. Effects of Crude Oil on Evaporation - Crude oil applied to the wet soil surfaces of the lysimeters following rains suppressed evaporation immediately following the rains. However, the value of the crude oil in preserving soil moisture over long periods needs further investigation. Diurnal Changes in Soil Moisture - Soil water content in the upper 30 cm (12 inches) of the soil apparently changes diurnally with major diurnal changes in soil temperature. Such changes may cause stress in young crop seedlings

Rapid Response Tensiometer for Evaluating Preplant Irrigation Efficiency

A study of the potential of using rapid response tensiometers to evaluate preplant irrigation was conducted at the Texas Agricultural Experiment Station, Lubbock and Halfway, Texas. Sites used for the study were an Olton loam soil at Lubbock and a Pullman clay loam at Halfway. Soil water potential was measured with both portable rapid response and permanently installed tensiometers. Soil water content was measured with a neutron probe. Since preirrigations are performed during freezing weather, it was necessary to develop a technique to keep the permanent tensiometers from freezing. Substituting a methanol-water mixture (30% by volume), the water in the tensiometers protected the tensiometers down to temperatures of -18.8¡C. Soil water potential values for "field capacity" (-14 to -17 cbars at 60 cm; -15 to -18 cbars at 120 cm) were significantly lower than those obtained during a previous study (-23 to -25 cbars at 60 cm; -34 to -35 cbars at 120 cm). Data obtained were insufficient to explain the differences. It was possible to install the rapid response tensiometers in 10 minutes or less. However, considerable problems were encountered once the rapid response tensiometers were installed. These included cracked bulbs and soil clay plugging the pores of the tensiometer bulbs which eventually resulted in slow response time and inaccurate readings. As long as the tensiometers were working properly, readings obtained compared favorably (within -5 cbars) with those from the permament tensiometers. Both permanently installed tensiometer and the neutron soil moisture probe provided good data for evaluating the efficiency of preplant irrigation from furrow irrigation. As expected, more water was applied to the soil close to the point of application with decreasing amounts applied with increasing distance from the point of application. The application efficiency was affected by the distance from the water source, flow rate, amount of water applied, and initial soil water content. Application efficiencies ranged from 22 to 76%. In general, the most efficient applications were those in which small amounts were applied to dry soils at fast flow rates. Infiltration rates calculated using rate of advance data were comparable to those previously determined with infiltrometers

Comportamento de genótipos de trigo cultivados em dois ecossistemas de terras baixas na metade sul do Rio Grande do Sul.

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Rendimento de grãos e fatores de produção de trigo em função da ocorrência de precipitação pluviométrica na fase reprodutiva.

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Manejo na cultura do trigo com finalidade de duplo propósito-forragem e grãos.

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Giant microwave photoresistance of two-dimensional electron gas

We measure microwave frequency (4-40 GHz) photoresistance at low magnetic field B, in high mobility 2D electron gas samples, excited by signals applied to a transmission line fabricated on the sample surface. Oscillatory photoresistance vs B is observed. For excitation at the cyclotron resonance frequency, we find an unprecedented, giant relative photoresistance (\Delta R)/R of up to 250 percent. The photoresistance is apparently proportional to the square root of applied power, and disappears as the temperature is increased.Comment: 4 pages, 3 figure

Controle da mortalidade por parasitismo gastrointestinal em filhotes de capivara (Hydrochaeris hydrochaeris) criados em sistema semi-intensivo.

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