Colin S. Campbell

Diel and seasonal variation in CO2 flux of irrigated rice

Abstract Rice is a primary food source for half the world’s population, but little is known of how temporal changes in the field-scale physical environment affect carbon dioxide exchange rate (CER), biomass accumulation, and crop yield. Experiments were conducted in 1998 and 1999 in a commercial field near El Campo, TX, to evaluate interactions between CER and the physical environment. Tower-based conditional sampling was used to measure CER. Environmental parameters such as photosynthetically active radiation (PAR), net radiation, and temperature were measured along with CER. Whole-plant biomass was also collected throughout both seasons. Fluctuations in diel CER were correlated with changes in PAR, while season-long trends in CER were associated with changes in leaf area index and stage of development. Crop yield was found to be directly related to total carbon-dioxide exchange after heading, and may have been affected by environmental conditions at anthesis, such as temperature and wind speed, or leaf nitrogen status, both of which differed considerably between the two seasons. Data showed a positive correlation between biomass accumulation and cumulative CER for both years of the study.

Thermal and Electrical Conductivity Probe (TECP) for Phoenix

Received 29 November 2007; revised 1 August 2008; accepted 30 November 2008; published 25 March 2009. [1] The Thermal and Electrical Conductivity Probe (TECP) is a component of the Microscopy, Electrochemistry and Conductivity Analyzer (MECA) payload on the Phoenix Lander. TECP will measure the temperature, thermal conductivity, and volumetric heat capacity of the regolith. It will also detect and quantify the population of mobile H2O molecules in the regolith, if any, throughout the polar summer, by measuring the electrical conductivity of the regolith as well as the dielectric permittivity. In the vapor phase, TECP is capable of measuring the atmospheric H2O vapor abundance as well as augmenting the wind velocity measurements from the meteorology instrumentation. TECP is mounted near the end of the 2.3 m Robotic Arm and can be placed either in the regolith material or held aloft in the atmosphere. This paper describes the development and calibration of the TECP. In addition, substantial characterization of the instrument has been conducted to identify behavioral characteristics that might affect landed surface operations. The greatest potential issue identified in characterization tests is the extraordinary sensitivity of the TECP to placement. Small gaps alter the contact between the TECP and regolith, complicating data interpretation. Testing with the Phoenix Robotic Arm identified mitigation techniques that will be implemented during flight. A flight model of the instrument was also field tested in the Antarctic Dry Valleys during the 2007–2008 International Polar Year.

Tower-based conditional sampling for measuring ecosystem-scale carbon dioxide exchange in coastal wetlands

Long-term measurements of CO2 exchange between coastal wetlands and the atmosphere are necessary to improve our understanding of the role these ecosystems play in the global carbon cycle, and the response of these systems to environmental change. We conducted research to adapt and evaluate tower-based conditional sampling as a method for measuring net CO2 exchange (NCE) at the ecosystem scale on a continuous basis. With conditional sampling, NCE is determined from the product of the standard deviation of vertical wind velocity, the difference in CO2 concentration between updrafts and downdrafts in the constant flux portion of the boundary layer above the surface, and an empirical coefficient. We constructed a system that used a sonic anemometer to measure vertical wind velocity (w) and control a high-speed three-way valve that diverted air from updrafts and downdrafts into separate sample lines, depending on the direction ofw. an infrared gas analyzer was used to measure the concentration difference. The conditional sampling system was installed and tested in a marsh in the Nueces River Delta near Corpus Christi, Texas, as part of a long-term study of effects of freshwater inflow on CO2 flux. System accuracy was evaluated by comparing conditional sampling measurements of water vapor flux with independent estimates obtained with the Bowen ratio method. Average daily flux estimates for the two methods agreed to within 13%. Measurements showed that freshwater inflow due to flooding of the Nueces River increased NCE by increasing CO2 assimilation and decreasing CO2 efflux. Over a 65-d period, daily NCE varied from a maximum gain of 0.16 mol CO2 m−2 d−1 during flooding to a maximum loss of −0.14 mol CO2 m−2 d−1 when the marsh dried. Our study showed that conditional sampling was well suited for quantifying CO2 exchange in coastal wetlands on a diel, daily, and seasonal basis.

Automatic irrigation scheduling of apple trees using theoretical crop water stress index with an innovative dynamic threshold

We developed an irrigation algorithm relying on a theoretical stress index (i.e. CWSI).A new, variable threshold for the CWSI was developed.Irrigation water was automatically delivered to the plots of apple trees.There was a high correlation between midday CWSI and stem water potential.The algorithm avoided over irrigation on humid, cool, and overcast days. An adaptive scheduling algorithm relying on a theoretical crop water stress index (CWSI) was developed to automatically irrigate apple trees. Unlike the traditional CWSI algorithm where the threshold is a constant value, in the present approach the threshold is dynamically determined by following the CWSI trend. A previous work on the energy budget analysis of a single apple leaf provided the base for calculating lower and upper boundaries of CWSI. To test the feasibility of the algorithm, it was applied to the thermal and meteorological data collected during the 2007 and 2008 growing seasons. A computer-based wireless control system was also developed to automatically schedule irrigations in three plots of apple trees in the 2013 growing season. In a small scale field experiment, two treatments were compared: (1) automatic irrigation using the new algorithm (CWSI-DT) and (2) irrigation scheduling based on weekly readings of neutron probe (NP). The soil water deficit under the CWSI-DT treatment was maintained within the well-watered range with no signs of over or under irrigation. This was better than the results in the NP treatment where there were occasions of under irrigation. Midday canopy and air temperature difference ( Δ T m ) exhibited a close agreement with midday stem water potential ( Ψ stem ; R2=0.63, p < 0.01 ). Normalizing Δ T m in the form of CWSI resulted in a much higher correlation between midday CWSI and midday Ψ stem (R2=0.91, p < 0.0001 ) suggesting CWSI as a reliable indicator of apple trees water status. The automatic control system running the new CWSI-DT algorithm was able to avoid over-irrigation under humid and cool weather conditions, and adapted itself to the changing conditions of the apple trees. The results of this study were promising in terms of using ground-based thermal sensing for automatic irrigation scheduling of sparse, discontinuous apple trees.

Comparison of irrigation automation algorithms for drip-irrigated apple trees

We developed a decision support system integrated with a wireless sensor network.We developed and field-tested seven irrigation scheduling algorithms for drip-irrigated apples.We used the time-temperature threshold (TTT) method in apple trees for the first time.The thermal-based treatments competed well with neutron probe (NP).Thermal/weather-based irrigation scheduling reduced applied water by about 70% compared with conventional irrigation. Seven irrigation scheduling algorithms and an automatic control system along with a wireless network of soil, thermal and weather sensors were developed and assessed in Prosser, WA in the growing season of 2013. The system was comprised of six wireless sensor and valve actuating nodes installed across an apple orchard, a central base station made up of a transceiver connected to a laptop, and a graphical user interface (GUI). The irrigation algorithms/treatments included the time-temperature threshold (TTT), crop water stress index with dynamic threshold (CWSI), soil-based using granular matrix sensors (SOIL), weather-based using a temperature-only-based evapotranspiration (ET) model and soil water balance (WB), a combination of SOIL and WB (SL+WB), a conventional irrigation practice used in the region (CNTRL), and soil-based using a neutron probe (NP) as benchmark. Different treatments were compared based on the total irrigation water (It) applied during the season. They were also compared based on simplicity and expense for a grower to implement. Soil water content (źs) and stem water potential (źstem) were monitored in a number of treatment plots. The total applied water for CNTRL was significantly higher than all other treatments (p<0.001). The thermal-based TTT and CWSI treatments applied the same amount of water as NP and WB (p<0.001). CWSI and TTT substantially reduced water applied (70%) while maintaining źstem within the non-stressed range. In addition, źs in the treatment plots of TTT and CWSI did not exceed the maximum allowed deficit recommended for apple trees (MAD of 50%) showing a strong agreement with NP. The SOIL and SL+WB treatments resulted in tangible under-irrigation as leaf drop, decreased leaf turgidity, growth reduction and abnormally small fruits were seen. Among all the strategies, WB seemed to bear the characteristics of being economical, easy to implement and fairly accurate. Our preliminary results also support the use of wireless sensor network for automatic irrigation management of drip-irrigated apple trees.

Direct Calculation of Thermodynamic Wet-Bulb Temperature as a Function of Pressure and Elevation

A simple analytical method was developed for directly calculating the thermodynamic wet-bulb temperature from air temperature and the vapor pressure (or relative humidity) at elevations up to 4500 m above MSL was developed. This methodology was based on the fact that the wet-bulb temperature can be closely approximated by a second-order polynomial in both the positive and negative ranges in ambient air temperature. The method in this study builds upon this understanding and provides results for the negative range of air temperatures (2178 to 08C), so that the maximum observed error in this area is equal to or smaller than 20.178C. For temperatures

A pragmatic, automated approach for retroactive calibration of soil moisture sensors using a two-step, soil-specific correction

08C, wet-bulb temperature accuracy was 60.658C, and larger errors correspondedto very high temperatures (Ta

Cold In-Place Recycling Moisture-Related Design and Construction Considerations for Single or Multiple Component Binder Systems

398C) and/or very high or low relative humidities(5%,RH,10% or RH . 98%). The mean absolute error and the root-mean-square error were 0.158 and 0.28C, respectively.

Constructing Fast, Accurate Soil Water Characteristic Curves by Combining the Wind/Schindler and Vapor Pressure Techniques

Individual laboratory calibration of many soil water content sensors is unpractical.We applied sensor-specific calibrations based on soil properties at insertion sites.This method is a retroactive approach for acquired sensor data.Produced accurate sensor values in a network installed across diverse soil profiles. Soil moisture sensors are increasingly deployed in sensor networks for both agronomic research and precision agriculture. Soil-specific calibration improves the accuracy of soil water content sensors, but laboratory calibration of individual sensors is not practical for networks installed across heterogeneous settings. Using daily water content readings collected from a sensor network (42 locations5 depths=210 sensors) installed at the Cook Agronomy Farm (CAF) near Pullman, Washington, we developed an automated calibration approach that can be applied to individual sensors after installation. As a first step, we converted sensor-based estimates of apparent dielectric permittivity to volumetric water content using three different calibration equations (Topp equation, CAF laboratory calibration, and the complex refractive index model, or CRIM). In a second, re-calibration step, we used two pedotransfer functions based upon particle size fractions and/or bulk density to estimate water content at wilting point, field capacity, and saturation at each sensor insertion point. Using an automated routine, we extracted the same three reference points, when present, from each sensors record, and then bias-corrected and re-scaled the sensor data to match the estimated reference points. Based on validation with field-collected cores, the Topp equation provided the most accurate calibration with an RMSE of 0.074m3m3, but automated re-calibration with a local pedotransfer function outperformed any of the calibrations alone, yielding a network-wide RMSE of 0.055m3m3. The initial calibration equation used in the first step was irrelevant when the re-calibration was applied. After correcting for the reference core measurement error of 0.026m3m3 used for calibration and validation, the error of the sensors alone (RMSEadj) was computed as 0.049m3m3. Sixty-five percent of individual sensors exhibited re-calibration errors less than or equal to the network RMSEadj. The incorporation of soil physical information at sensor installation sites, applied retroactively via an automated routine to in situ soil water content sensors, substantially improved network sensor accuracy.

Frequency, electrical conductivity and temperature analysis of a low-cost capacitance soil moisture sensor

In recent years, cold in-place recycling (CIR) has gained momentum because of its economic, performance, and sustainability characteristics; as a result CIR markets are likely to expand into, for example, higher traffic routes. To further understand how to continue improving CIR for existing applications as well as future applications, better techniques are needed with regard to interfacing design and construction. Moisture is one key area in which design and construction are often disconnected. This study’s objective, therefore, was to evaluate the moisture (and associated early-age strength and stability) aspects of CIR, particularly within a framework that could consider hydraulic cement, bituminous emulsion, or combinations of both binders. A universal design framework that accommodates any binder or combination thereof while representing early-age field conditions has advantages for agencies, not only in its reasonable characterization of construction processes, but also in its facilitation of competition and creativity in the process of selecting materials and proportions. This study was organized in three phases. Phase 1 documented moisture instrumentation of a cement CIR project. Data were successfully obtained throughout compaction and curing and were used in Phases 2 and 3 alongside supplemental field and laboratory testing. Phase 2 evaluated moisture’s role in compaction; Phase 3 evaluated moisture–strength and moisture–stability relationships for various curing protocols. Phase 2 concluded that high (>6%) moisture content, typical of Proctor compaction, is generally unnecessary. Thus, Proctor compaction is discouraged in favor of a fixed design moisture content. Phase 3 concluded that humid (35% to 50% humidity) and dry 40°C oven curing protocols are candidates for universal CIR design.