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The large extension and diversity of the Cerrado vegetative cover, the second largest biome in South America, has a strong impact on regional, and possibly global, energy, water, and carbon balances. Nevertheless, as a major farming frontier in Brazil, it is estimated that about 40% of the Cerrado land cover has already been converted into cultivated pastures, field crops, urban development, and degraded areas. Despite this aggressive pace of land conversion, there have been few investigations on the operational utilization of remote sensing data to effectively monitor and understand this biome. Within this context, and within the goals and framework of the Large Scale Biosphere-Atmosphere Experiment in Amazonia (LBA), we evaluated the usefulness of spectral vegetation indices (VIs), to effectively monitor the Cerrado, detect land conversions, and discriminate and assess the conditions of the major structural types of Cerrado vegetation. Using a full hydrologic year (1995) of AVHRR, local-area-coverage (LAC), data over the Cerrado, converted to normalized difference vegetation index (NDVI) and soil adjusted vegetation index (SAVI), we were able to spatially discriminate three major communities based on their phenologic patterns. These included savanna formations and pasture sites, forested areas, and agricultural crops. We also analyzed wet and dry season, aircraft-based radiometric data and a ground-based set of biophysical measurements, collected over the Brasilia National Park (BNP), the largest LBA core site in the Cerrado biome. Overall, we found the MODIS vegetation indices, which include a continuity NDVI and the new enhanced vegetation index (EVI), to provide better performance capabilities with improved dynamic ranges and contrasts in seasonal dynamics. Land cover discrimination was favored by the NDVI, while the EVI more strongly responded to the seasonal contrast of the vegetative cover. Thus, the synergistic use of the MODIS VI products will very likely result in an improved monitoring capability and understanding of the Cerrado biome.

A greenhouse lysimeter experiment was performed to evaluate the use of in-situ bioremediation and phyto-remediation to reduce mineral oil concentrations in a weathered contaminated soil. The hypotheses for the study were (1) a combination of microbial- and phyto-remediation would yield a best remediation strategy, and (2) the addition of low levels (10 mg/L) of a biosurfactant would stimulate and increase the rate of remediation by increasing the bioavailability of the mineral oil in the soil. The results indicate, on average, a higher rate of mineral oil removal occurred in planted lysimeter tanks versus non-planted lysimeter tanks. Specifically, for unplanted treatments an average of 22% of the mineral oil was removed in 24 weeks in comparison to the planted treatments for which an average of 54% of the mineral oil was removed. The effect of application of fertilizer on mineral oil degradation was unclear, but a visual inspection showed that vegetated tanks receiving fertilizer had better growth. No conclusions can be made regarding the addition of biosurfactant. Though a couple of the lysimeter tanks receiving biosurfactant performed relatively well, overall, the results were inconclusive. Enumeration of mineral oil degraders showed that there was a statistical difference between planted tanks and unplanted tanks with planted tanks having higher numbers. These results help support the conclusion that plants enhanced mineral oil degradation. Enumeration of total heterotrophs showed that there was no statistical significant difference between the planted and unplanted treatments. In conclusion, this study demonstrated that a low-cost, low-maintenance approach to facilitate remediation of weathered mineral oil contaminated soil is a combination of microbial- and phyto-remediation.

The assessment of environmental degradation from farming practices has received recent attention due to the concern for sustainable agriculture. The United States Department of Agriculture and the Environmental Protection Agency have set forth the Unified National Animal Feeding Operation Strategy to protect the nation's water resources from contamination. The Unified Animal Feeding Operation Strategy requires that field application of manure, a common fertilization method and manure disposal practice, may not exceed crop nutrient needs. This requirement necessitates studies to determine how the multiple variables involved interact so that farmers may comply with the regulation. In this research, the effects of the application of manure, both fresh and composted, on a production alfalfa (Medicago sativa L.) field was examined. Manure and compost were applied to a production alfalfa field to determine the impact on alfalfa yield, soil nutrient content, and the potential for nitrate leaching. A conventional "no nitrogen added" treatment was also maintained as a control. Manure and compost were applied after each harvest in amounts such that the amount of nitrogen removed in the alfalfa harvest was replaced with the same amount of nitrogen in manure or compost. Application rates varied from 35 to 476 kg nitrogen ha⁻¹ after each harvest. It was found that the finer particles of the compost incorporated into the soil profile better than the chunky form of the manure. Soil analysis down to 150 cm depth showed that the compost treatment plots contained nearly 3000 kg total nitrogen ha⁻¹, the manure plots contained about 1750 kg ha⁻¹, and the no nitrogen plots had approximately 1400 kg ha⁻¹. Final PO₄-P soil analysis revealed that compost plots contained about 125 kg PO₄-P ha⁻¹, manure plots had approximately 115 kg ha⁻¹, and no nitrogen plots had only 20 kg ha⁻¹. Alfalfa yield did not vary between treatments throughout the one and a half year study. Also, no detectable nitrate or phosphate was found in the leachate collected from each of the treatments.

Nitrate contamination of surface and groundwater has become a serious concern in many agricultural areas throughout the world. The major source of nitrate contamination is believed to be nitrogen fertilizer from agricultural fields. Best Management Practices have been developed to guide fertilizer use and minimize nitrogen losses, but do not address control of nitrate movement from the crop root zone. It is proposed that an in-situ method, electrokinetics (EK), could be used to control nitrate movement, retaining it near the root zone. Lysimeter experiments were conducted to evaluate the effect of parallel electrodes on pH and nitrate distribution in field soils subjected to an electrical input. However, the expected results, increased nitrate retention, reduced sodium and calcium concentration and lower pH values near the anode, were not attained consistently in the test soils with and without Sudan grass. Small scale experiments in a vertical, partially saturated sandy soil column (25 cm height by 14 cm diameter) were conducted to evaluate the optimal EK parameters. After 80 mA current for 6 h the nitrate was retained near the anode, with the highest measured nitrate concentration of 7155 mg/L within 5 mm of the anode. The nitrate concentration at the cathode was 1/5 of the inflow solute concentration (221 mg/L). The pH was 11 near the cathode, 3.5 near the anode, and showed little changes in intermediate layers. The results demonstrate that in sandy soils nitrate can be strongly retained near the anode, even against gravity effect. As the percentage of illite clay in the soil increased, the EK effect decreased; due to the increase of fine clay particles both the transports of ions and the water were inhibited. The loam soil showed some increase in the nitrate concentration near the anode, but the clay soil showed no change. An increase of pH near the cathode was seen in all soils. The electrical potential analysis showed the sandy soil required the highest electrical potential 97.23 V, loam soil was 18.24 V and clay soil was 14.22 V.

In constitutive modeling, one of important tasks is to calibrate the model. To calibrate a model is to find out the values of the model parameters for a material whose stress-strain behavior is to be simulated by the model. Conventional approach is to find certain well-defined states ill certain tests where behavior of a material is controlled by those parameters and then the stress and strain and other history parameters at those states can be used to find them. However, as the model evolves more sophisticated, such as the Disturbed State Concept Model (DSC), in which a greater number of parameters are introduced to account for behavior of the material under various stress conditions, it is not possible to find an easy way to calibrate, mainly due to certain stress-strain states are difficult to be isolated out. In this study an optimization approach is proposed by using quasi-Newton method with BFGS up-dating scheme. Contrary to the conventional approach which determines parameter values by averaging values of laboratory tests or by simple data fitting of the assumed parameter relations, the optimization approach is to find the best agreement of the model simulation with the experimental observation, then gives a set of parameter values for the best agreement which is quantitatively measured by the least error residual. Weight is used in the optimization procedure to emphasize on better simulation agreement with the observation for certain stress path conditions. This weight can be decided based on the engineering judgment for certain practical problems. By using the DSC model to simulate stress-strain response of various laboratory tests of sands, and by using the DSC model in a finite element analysis to simulate dynamic soil-structure interaction response of a shaking table test for saturated soil, it is shown that the optimization approach yields closer agreement with the observation. Based on the proposed optimization approach, a computer program DSCOPT is developed for the DSC model. The program takes the laboratory test data as input and outputs the model parameter values by the conventional and optimized approaches, and graphics plots of the model simulation.

In an effort to determine the agronomic necessity of K fertilization of cotton (Gossypium spp.) in Arizona, a five-year study was initiated in 1991, with a single field study near Gila Bend. Subsequent sites selected ranged from western (Yuma) to eastern (Safford) Arizona which totaled 11 site-years. Both Upland (G. hirsutum L.) and Pima (G. barbadense L.) cottons were cultivated, using soil and foliar applications of K. In 1992, study sites included the Safford Ag. Center (SAC), Maricopa Ag. Center (MAC), and a fanner cooperator site at Coolidge. In 1993, the experiment stations (SAC and MAC) were continued and Yuma Valley was added. The 1994 sites included only the experiment stations (SAC and MAC). In 1995, SAC and MAC were again maintained and a third location, a fanner cooperator site at Buckeye was added. Results from the study (12 site-years) indicated no lint yield increases due to K fertilization in all locations with either Upland or Pima cotton However, in 1995 at Buckeye, the result revealed a significant yield reduction due to the K foliar treatments. There were, however, no significant differences among the soil-only or the soil- plus-foliar treated plots at this location. Potassium (K) release kinetics of clay samples from 10 agricultural representative soils of Arizona was determined by successive extraction using a Ca-saturated cation resin. A preseason physical and chemical characterization of the soils showed all soils contain smectite-mica minerals. Four mathematical models (power function, Elovich, parabolic diffusion and first-order) were used to describe the nonexchangeable K release reaction involving 700-hour cumulative extraction time. Comparison of the models using the coefficient of determination (r²) and the standard error of the estimate (SE) indicated that the Elovich and the power function equations overall displayed the best fit. The first-order, and for the most part, the parabolic diffusion equation did not describe the K release very well. The constants a (initial rate) and b (release rate) for the Elovich and the power function equations, are at least in the order of magnitude as those found by others in several previous studies.