Paul R. Bullock

The Soil Moisture Active Passive Validation Experiment 2012 (SMAPVEX12): Prelaunch Calibration and Validation of the SMAP Soil Moisture Algorithms

The National Aeronautics and Space Administration (NASA) Soil Moisture Active Passive (SMAP) satellite is scheduled for launch in January 2015. In order to develop robust soil moisture retrieval algorithms that fully exploit the unique capabilities of SMAP, algorithm developers had identified a need for long-duration combined active and passive L-band microwave observations. In response to this need, a joint Canada-U.S. field experiment (SMAPVEX12) was conducted in Manitoba (Canada) over a six-week period in 2012. Several times per week, NASA flew two aircraft carrying instruments that could simulate the observations the SMAP satellite would provide. Ground crews collected soil moisture data, crop measurements, and biomass samples in support of this campaign. The objective of SMAPVEX12 was to support the development, enhancement, and testing of SMAP soil moisture retrieval algorithms. This paper details the airborne and field data collection as well as data calibration and analysis. Early results from the SMAP active radar retrieval methods are presented and demonstrate that relative and absolute soil moisture can be delivered by this approach. Passive active L-band sensor (PALS) antenna temperatures and reflectivity, as well as backscatter, closely follow dry down and wetting events observed during SMAPVEX12. The SMAPVEX12 experiment was highly successful in achieving its objectives and provides a unique and valuable data set that will advance algorithm development.

Persistent organic pollutants and mercury in the Himalaya

Persistent organic pollutants and mercury are important contaminants due to their persistence in the environment and potential toxic effects on ecosystems and humans. Concerns related to these contaminants are particularly pertinent in Asia where the use of pesticides and mercury emissions have been increasing dramatically due to changing agricultural practices and rapidly expanding industrialization. Based on studies in European and North American mountain regions, evidence is increasing that alpine regions function as regional convergence zones for selected organic pollutants due to an effect called orographic cold trapping. It is hypothesized that such an effect may be particularly pronounced in the Himalaya because of dramatic elevational temperature and precipitation gradients relative to contaminant source regions in its immediate vicinity, and because of the regional monsoon system that has been shown to deliver particles and inorganic air pollutants to higher altitudes. A review of studies of persistent organic pollutants and mercury in the Himalayan ecosystem reveals that measurements of these contaminants are sparse and rarely adhere to strict quality control procedures, making it difficult to judge whether relatively high concentrations reported for these materials are indeed an indication of efficient transfer of toxic contaminants to Himalayan ecosystems. Knowledge gaps are identified and suggestions are made for research that would allow for the testing of the hypothesis that the Himalaya is an important cold trap for semi-volatile organic contaminants and mercury.

Genotypic and environmental variation in grain, flour, dough and bread-making characteristics of Western Canadian Spring Wheat

Wheat (Triticum aestivum L.) grain, flour, dough and bread quality characteristics are strongly influencedby growing-season weather conditions. Understanding the impact of genotype, environment, and their interactions on Canadian wheat quality is important for Canada to maintain its high standard for delivery of consistent quality wheat to domestic and international customers. The effects of genotype, environment and genotype by environment (G × E) interaction on numerous grain, flour, dough and bread-making characteristics were assessed. The Canadian Western Red Spring (CWRS) cultivars were AC Barrie, Superb, AC Elsa, and Neepawa; the Canadian Prairie Spring (CPS-white) cultivar was AC Vista; and the Canadian Western Hard White Spring (CWHWS) cultivar was Snowbird. These genotypes were grown at five locations across the Canadian prairies in 2 yr to provide a total of 7 site-years of milling quality wheat for analysis. Genotype, environment and their interactions had significant effects on most parameters...

Thermal time models for estimating wheat phenological development and weather-based relationships to wheat quality

Accurate prediction of crop phenology is a key requirement for crop development models. The prediction of spring wheat yield and quality from meteorological data can be improved by quantifying heat and moisture conditions during specified phenological phases; therefore, accurate prediction of phenological development is important for estimating weather impacts on wheat quality. The objective of this study was to test the accuracy of biometeorological time (BMT), growing degree days (GDD), and physiological days (Pdays) for prediction of wheat phenological stages and impacts of growing season weather during those stages on wheat bread-making quality. Observed crop phenological stages and detailed weather data across 17 site-years in western Canada for six hard spring wheat varieties were collected to assess BMT, GDD and Pdays. Biometeorological time was most consistent for predicting the length of the seeding to jointing and seeding to anthesis growth stages and second most consistent behind GDD for predic...

Estimating canola (Brassica napus L.) yield potential using an active optical sensor

Active optical sensors have potential as tools to increase N fertilizer use efficiency in crop production; however, empirical data are required to utilize the sensors for this purpose. Data were compiled from N fertilizer trials at five Canadian locations (2004-2007) to determine the feasibility of using optical sensors during the growing season to estimate the seed yield potential of canola (Brassica napus). The normalized difference vegetation index (NDVI) of each plot in each trial was measured using a hand-held optical sensor several times each season. The NDVI between the six-leaf stage and the beginning of flowering was divided by one of several different heat unit summations to normalize the measurements, and data were combined across locations. Linear and exponential regression analyses were completed for canola seed yield as a function of both the original and normalized NDVI measurements. When data from all locations were combined, NDVI was significantly correlated with canola seed yield (R2 = 0...

Bromide redistribution as influenced by landscape morphology and pedogenic properties in a variable glacial till landscape: A qualitative examination

Redistribution of water and associated solutes in undulating to hummocky landscapes affects crop yield via losses of valuable nutrients and negatively impacts groundwater quality. The objective of this study was to determine the influence of qualitative soil-landscape complexes on vertical and lateral redistribution of solutes in a variable glacial till landscape under zero tillage agricultural management by employing a bromide tracer. Tracer plots were established in the fall of 1999 within three sites comprising three representative soil-slope associations. Values of soil development indicators (A horizon thickness, solum thickness, depth to CaCO3, profile development index and organic carbon) generally increased from crest to midslope to depression. Further to this, the occurrence and thickness of eluvial and illuvial horizons increased from crest to midslope to depression. Well-developed, clay-coated blocky Bt horizons with vertical cracking and overlying Ae horizons in depressions appeared to have fa...

Near-infrared spectroscopy for soil water determination in small soil volumes

Critical soil water levels for soil microscale processes are difficult to determine because of variability in large soil volumes and lack of techniques for logging soil water contents in small soil volumes. This study tested nearinfrared (NIR) spectroscopy for soil water content determination. Five soil horizons with a range in soil texture, soil organic carbon, carbonates, pH and horizon depth, were tested at air-dry, field capacity and 0.1 MPa tension water content. Volumetric soil water content, determined using the standard method of oven-drying and soil bulk density, was compared to NIR absorbance in various combinations and wavelengths. The NIR spectra obtained with the probe in direct contact with the soil gave better results than when the probe was separated from the soil with a glass slide. The most reliable validation results were obtained using a multivariate partial least squares regression of the full spectrum with an r2 of 0.95 and RMSE of prediction of 6.4%. Smoothing and derivatives of the...

Modeling the Soil-water Retention Characteristic With Pedotransfer Functions for Shallow Seedling Recruitment

The soil-water retention characteristic (SWRC) is a necessary parameter in seedling recruitment studies. The SWRC was investigated for three 25-mm increments of the shallow seedling recruitment zone to a depth of 75 mm at three hillslope positions on two hillslope aspects across cultivated field topography. Volumetric water content was determined at matric potentials from saturation to −1.5 MPa for the middle soil increment. Three local pedotransfer functions (PTF) were developed using basic soil physical properties and detailed particle size distribution to estimate the parameters of the van Genuchten model for the middle soil increment. The local PTF were compared with Rosetta, HYPRES, and SOILPROP regional PTF. The local PTF generally predicted water retention better than the regional PTF. Rosetta H4 and H5 models predicted water retention as well as one of the local PTF. The SWRC in the upper and lower soil increments were estimated by local PTF using soil properties from the upper and lower increments coupled with the estimated SWRC from the middle increment. Soil properties used to parameterize local PTF varied with soil depth; however, SWRC did not differ with depth. Where direct measurement of soil hydraulic properties is resource limiting, accurate estimation of local SWRC by regional PTF is possible; however, input of partial water retention information was necessary to achieve accuracy. Using local PTF to estimate the SWRC in the upper and lower profile increments of the seedling recruitment zone indicates that a single SWRC is sufficient to describe the profile in this study.

Optical sensors have potential for determining nitrogen fertilizer topdressing requirements of canola in Saskatchewan

An important challenge in N management is matching fertilizer inputs to crop requirements for specific environmental conditions. Field experiments were completed over 3 yr at two locations in Saskatchewan to evaluate the feasibility of using optical sensors and high-N reference plots along with topdressed liquid urea ammonium-nitrate (UAN) to arrive at more optimal N rates for canola (Brassica napus L.). Treatments included N management strategies where the timing and methods of application were varied along with the total quantities of N applied. Sensor-based N management was compared with the predominant practice of banding predetermined amounts of N at seeding. On average, sensor-based N management resulted in a 34 kg N ha-1 reduction in fertilizer use with no effect on seed yields except at Indian Head in 2006 where dry conditions resulted in yield reductions of 370 to 454 kg ha-1 compared with applying canolas entire N requirements at seeding. Sensor-based N management or split-N applications never ...

A comparison of growing season agrometeorological stress and single-date Landsat NDVI for wheat yield estimation in west central Saskatchewan

Modeled moisture stress from three weather stations and normalized difference vegetation index (NDVI) values from historical Landsat images for an area of west central Saskatchewan were utilized to assess the yield potential of several wheat fields, some of which were suspected to have suffered residual herbicide damage. The study was initiated to assess whether the crop yields in recent years had been adversely affected by residual herbicide damage. There was a wide variation in wheat yields between fields within a growing season and between growing seasons. NDVI values from individual fields could not provide a reliable estimate of wheat yield. However, a linear regression of mean annual producer-reported wheat yields on mean growing season moisture stress from three weather stations that surrounded the study area was significant with a coefficient of determination (r2) of 0.85. Although mean annual producer-reported wheat yields showed a direct relationship with mean NDVI, the regression was not significant. Mean NDVI was also poorly correlated with mean growing season moisture stress. This may be partly related to the inability to source cloud-free Landsat images from late July when the wheat would normally be near peak growth. A within-year comparison of individual yields and NDVI values for fields that had been treated and those that had not been treated with herbicide showed that there was no statistical difference between them.