No description available.

Although the drying process can improve the overall quality and usefulness of forest products, if drying is not carefully controlled, drying loss can be substantial. As most drying defects occur when the lumber moisture content is above fiber saturation point (FSP), measurement of moisture content (MC) above FSP is critically important. In this study, a technique was developed which permits use of an electrical resistance moisture meter RDX-1 (Delmhorst Instrument Company) to measure MCs of red oak and yellow-poplar during drying when MC is above FSP. The Lignomat in-kiln probe electrode was used throughout experiments. Two experiments were conducted. The first dealt with developing a two-point technique to measure MC above FSP. The other evaluated the effect of the moisture gradient on the MC reading from the meter. During the drying, pin electrode also was used when oven-dry MC was about 40% in order to compare the MC readings by the pin electrode and the probe electrode. The experimental results show the correlation between the MC readings and oven-dry MC of the sample is quite high during drying; the correlation of each sample is higher than 0.9. Based on this relationship, two-point technique of measuring MC above FSP was developed. This technique can predict MC above FSP of red oak within 5%, and the MC of yellow-poplar within 10%. From the experiment, it was found, when MC is above FSP, MC readings measured by probe electrodes are significantly different from those measured by pin electrodes. It was also found that the moisture gradient affects the MC readings dramatically. The depths of probes inserted into the boards are an important parameter for measuring MC. Different depths yield different MC readings. / Master of Science

Water is a scarce resource used by various stakeholders. Agriculture is one of the users of this resource especially for growing plants. Plants need to take up carbon dioxide to prepare their own food. For this purpose plants have stomatal openings. These same openings are used for transpiration. Quantifying transpiration is important for efficient water resource management and crop production because it is closely related to dry matter production. Transpiration could be measured using a number of methods or calculated indirectly through quantification of the soil water balance components using environmental instruments. The use of models such as the Decision Support System for Agrotechnology Transfer (DSSAT v3.5) is, however, much easier than environmental instruments. Nowadays, with increased capabilities of computers, the use of crop simulation modelling has become a common practice for various applications. But it is important that models, such as DSSAT v3.5, be calibrated and verified before being used for various applications such as long-term risk assessment, evaluation of cultural practices and other applications. In this study the model inputs have been collected first Then the model was calibrated and verified. Next sensitivitY analysis was carried to observe the model behavior to changes in inputs. Finally the model has been applied for long-term risk assessment and evaluation of cultural practices. In this study, the data collected formed the basis forthe minimum dataset needed for running the DSSAT v3.5 model. In addition, the factory given transmission of shading material over a tomato crop was compared to actual measurements. Missing weather data (solar irradiance, minimum and maximum air temperature and rainfall) were completed after checking that it was homogeneous to measurements from nearby automatic weather station. It was found that factory-given transmission value of 0.7 of the shade cloth was different from the actual one of 0.765. So this value was used for conversion of solar irradiance measured outside the shade cloth to solar irradiance inside the shade cloth. Conventional laboratory procedures were used for the analysis of soil physical and chemical properties. Soil water content limits were determined using texture and bulk density regression based equations. Other model inputs were calculated using the DSSAT model. Crop management inputs were also documented for creation of the experimental details file. The DSSATv3.5 soil water balance model was calibrated for soil, plant and weather conditions at Ukulinga by modifying some of its inputs and then simulations of the soil water balance components were evaluated against actual measurements. For this purpose half of the data available was used for calibration and the other half for verification. Model simulations of soil water content (150 to 300 mm and 450 to 600 mm) improved significantly after calibration. In addition, simulations of leaf area index (LA!) were satisfactory. Simulated evapotranspiration (E1) had certain deviations from the measured ET because the latter calculated ET by multiplying the potential ET with constant crop multiplier so-called the crop coefficient. Sensitivity analysis and long-term risk assessments for yield, runoff and drainage and other model outputs were carried out for soil, plant and weather conditions at Ukulinga. For this purpose, some of the input parameters were varied individually to determine the effect on seven model output parameters. In addition, long-term weather data was used to simulate yield, biomass at harvest, runoff and drainage for various initial soil water content values. The sensitivity analysis gave results that conform to the current understanding of the soil-plant atmosphere system. The long-term assessment showed that it is risky to grow tomatoes during the winter season at Ukulinga irrespective of the initial soil water content unless certain measures are taken such as the use of mulching to protect the plants from frost. The CROPGRO-Soya bean model was used to evaluate the soil water balance and gro'W1:h routines for soil, plant and weather conditions at Cedara. In addition, cultural practices such as row spacing, seeding rate and cultivars were also evaluated using longterm weather data. Simulations of soil water content were unsatisfactory even after calibration of some of the model parameters. Other model parameters such as LAI, yield and flowering date had satisfactory agreement with observed values. Results from this study suggest that the model is sensitive to weather and cultural practices such as seeding rates, row spacing and cultivar maturity groups. The general use of decision support systems is limited by various factors. Some of the factors are: unclear definition of clients/end users; no end user input prior to or during the development of the DSS; DSS does not solve the problems that the client is experiencing; DSS do not match their decision-making style; producers see no reason to change the current management practices; DSS does not provide benefit over current decision-making system; limited computer ownership amongst producers; lack of field testing; producers do not trust the output due to the lack of understanding of the underlying theories of the models utilized; cannot access the necessary data inputs; lack of technical support; lack of training in the development ofDSS software; marketing and support constraints; institutional resistances; short shelf-life of DSS software; technical constraints, user constraints and other constraints. For successful use of DSS, the abovementioned constraints have to be solved before their useful impacts on farming systems could be realized. This study has shown that the DSSAT v3.5 model simulations of the soil water balance components such as evapotranspiration and soil water content were unsatisfactory while simulations of plant parameters such as leaf area index, yield and phonological stages were simulate to a satisfactory standard. Sensitivity analysis gave results that conform to the current understanding of the soil-plant -atmosphere system. Model outputs such as yield and phonological stages were found to sensitive to weather and cultural practices such as seeding rates, row spacing and cultivar maturity groups. It ha been further investigated that the model could be used for risk assessment in various crop management practices and evaluation of cultural practices. However, before farmers can use DSSAT v3.5, several constraints have to be solved. / Thesis (M.Sc.)-University of Natal, Pietermaritzburg, 2003.

A ground-based near-infrared spectroradiometer was built and used to measure relative spectral reflectance from cumulus congestus and cumulonimbus clouds during the 1985 and 1986 Arizona summer monsoon seasons. Thermodynamic phase was inferred from spectral features in the regions between 1.55-1.75μm and 2.1-2.3μm where there are distinct differences between absorption in liquid water and ice and absorption by water vapor is very weak. Although liquid water and ice are nearly transparent in the visible, they absorb weakly in the near-infrared and that absorption is amplified by multiple scattering in clouds. Reflectance measurements are simple to make, requiring neither high spectral resolution nor absolute detector response. Three distinct aspects of differences between absorption in liquid water and ice were used to infer phase: (a) Ratio of the signal at 1.65 μm to that at 2.2 μm; (b) Wavelength of peak signal in the 1.65 μm water vapor transmission window; (c) Half-bandwidth of the 2.1-2.3 μm feature. Representative spectra are presented and analyzed on the basis of the predicted behavior of liquid water and ice cloud absorption. The results are consistent with young cumuli rapidly glaciating as they reach cooler levels, well before evidence of anvil formation or fibrous structure, contrary to the notion that phase can be inferred from visible cloud features.

Spatial variation of in situ available water content was studied along with related parameters over three 16-ha irrigated fields. The fields, two near Marana (Pima County, Arizona) and one near Casa Grande (Pillai County), range in texture from very fine loam to loamy sand. All soil series present are mapped as Entisols or Aridisols. A 50-m grid provided 56 sampling sites in each field. Each site was sampled at 30, 60, 90, 120 and 150 cm. Samples were collected from each field following a heavy irrigation in March 1977. Bulk samples were collected two days and four weeks after the application of approximately 300 mm of water, to determine in situ water content at field capacity and moisture redistribution with time. Related parameters such as particle size distribution and soil water characteristics were also studied. Bulk density and saturated hydraulic conductivity were determined from undisturbed, core samples. The measured parameters showed different patterns of variation within the same field as well as from one field to the other. Spatial variability of saturated hydraulic conductivity was the highest for which coefficient of variability (CV) ranged upward to 108%. Bulk density, on the other hand, showed the lowest coefficient of variability, as low as 5%. The in situ available water content (AWC), estimated by subtracting moisture content at 15 bars from the corresponding in situ FC values, showed a general tendency to increase with depth corresponding to the increase in percent silt plus sand with depth in all three fields. The coefficient of correlation between the two parameters was high (up to 0.70). The mean values of AWC as estimated using 0.1 bar values for field capacity in the laboratory were consistently higher than the in situ values. The values were within 25 - 35% of each other in Fields 1 and 2, while in the sandier soil of Field 3, the AWC was overestimated by an average of 74% in the laboratory. The CV showed an irregular tendency to increase with depth, but was consistently high in the 150 cm layer in all three fields. Values estimated in the laboratory showed lower CV and higher correlations with soil separates than in situ AWC in all three fields. These two observations can be attributed to the elimination of in situ factors such as texture stratification, compaction, and/or amount of water applied. Agricultural soil formed on water transported material at 0.1 bar were highly correlated with sand (r = -0.8) and the 15 bar values were better correlated with clay (r = 0.5). Also, the coefficient of variability increased consistently with decreases in moisture content. The analysis of variance showed the three fields to be heterogeneous. The variation for within and between the 5 depth groups was significant. A two-way interaction between depths and subareas within each field accounted for 44, 45 and 38% of the total variability in Fields 1, 2, and 3 respectively. Cumulative frequency distribution plots, full normal plots, Kolmogorov-Smirnov tests of goodness-of-fit, tests of skewness and tests of kurtosis were conducted to test the null hypothesis of normal distribution for each parameter. The full normal plots, being sensitive to deviations from normality, rejected the null hypothesis in all cases with few exceptions. They showed the data tends to be skewed to the right and/or kurtic. The alternative frequency distribution of the parameters indicated the data to be asymmetric, short tailed with the exception of percent sand which was symmetric, short tailed for all three fields. A power transformation is suggested as a possibility for transforming the data to get near normal distribution.

No description available.

Call number: LD2668 .T4 1986 S237 / Master of Science / Agronomy

No description available.

Graduation date: 1994

Soil solution samplers have certain inadequacies that limit their range of possible applications. Passive Capillary Samplers (PCAPS), which apply suction to the soil pore-water via a fiber glass wick, have shown promising results in preliminary experiments in regard to collection efficiency of water and of bromide tracers. The objectives of this study were to evaluate PCAPS under non-steady state field conditions with respect to (1) effect of installation procedure and operational characteristics, (2) ability to estimate the soil-water flux, and (3) ability to estimate the mean concentration of agrochemicals. At the same time, samplers were used to (4) evaluate the effect of a cereal rye (Secale cereale (L.)) cover crop on NO₃⁻ leaching. Thirty-two PCAPS and 32 suction cup samplers were installed below the root zone at a depth of 120 cm in a Willamette Variant loam wet soil (fine loamy mixed mesic Pachic Ultic Argixeroll). Samplers were installed in an ongoing cover crop/crop rotation study. Regarding overall performance, flux measurements were within 20 % of the native values as determined by a water balance. The air release from the sample bottles was a point of concern and might have slowed down the sampling rate. The installation procedure introduced bias into volume and concentration measurements of the part of the PCAPS closest to the refilled trench. The leachate concentration as calculated using the arithmetic mean of suction cup sampler measurements holds a significant bias, deviating by up to 97 % for bromide concentrations. Phosphate was not detected by the suction cup samplers indicating that ceramic cups should not be used for phosphate sampling. Matrix and preferential flow could clearly be distinguished using the PCAPS, showing that PCAPS are a valuable tool to assess the hydrology and solute transport mechanisms of a field site. The cover crop reduced NO₃⁻-N leaching significantly at the recommended N rate as evaluated by PCAPS. The cover crop reduced the seasonal mean NO₃⁻-N concentration at the recommended N rate from 13.5 mg LI to 8.1 mg L⁻¹, which is under the E.P.A. drinking water quality standard of 10 mg L⁻¹. The total NO₃⁻-N mass lost under the fallow treatment at the recommended N rate was 48 kg N ha⁻' which compares to 32 kg N ha⁻' under the cover crop treatment. Given the increasing problems with nitrate contamination of ground water, programs to support the cultivation of catch crops in conjunction with nitrogen soil testing should be considered as a relatively easy, effective, and biologically sound means to reduce nitrate concentrations in the recharge to the ground water in agricultural settings. / Graduation date: 1994