Maize grain yield is often highly influenced by the genotype-by-environment (GxE) interactions which limit plant breeders’ ability to select for superior performance as variation in line performance exists across different environments. While studies have focused on the genetic components underlining GxE interactions, few have investigated the environmental components. The focus of this thesis was to investigate the role that soil moisture stress plays in the formation of GxE patterns using a unique set of hybrid recombinant inbred lines (RIL) that exhibit minimal phenological differences. With the use of environmental groups (EG, environments with similar GxE patterns), the field trials demonstrated that different EGs form when relative soil moisture stress is moderate to high; however, relative low soil moisture stress did not appear to influence the formation of GxE patterns. Seasonal corn heat unit (CHU) accumulation among EGs was the likely cause for EG differentiation among the low moisture stress EGs. It appears that CHUs were the primary cause of different GxE patterns forming when they did not exceed the recommended CHU for a population and when CHU differed greatly from one environment to another. When CHU were not limiting different GxE patterns formed based on the relatively moderate to high soil moisture stress conditions within the growing season. / Ontario Research Fund, National Science and Engineering Research Council, and The Ontario Ministry of Agriculture, Food and Rural Affairs.

A one year water table management field study was conducted on a Soulanges sandy loam soil in Soulanges county, Quebec. Two controlled water table levels, i.e. 0.5 m and 0.75 m from the soil surface, as well as free outlet conventional drainage treatments were established in monocropped corn (Zea mays L.) and corn intercropped with ryegrass (Lolium multiflorum Lam) plots. / Cropping system showed no significant effects on evapotranspiration, and on soil moisture distribution. It was observed that the 0.5 m and 0.75 m controlled water tables (CWT) provided the same soil moisture trends in both cropping systems. The soil moisture was always higher in controlled water table plots compared to freely drained plots. The water use efficiency of 0.75 m CWT in both cropping systems was high compared to 0.5 m CWT. / The soil moisture contents at three depths were only 2% to 10% less in intercropped plots compared to monocropped plots. The soil moisture was 12 to 13% higher in CWT plots compared to freely drained plots for both cropping systems. The soil moisture in 0.5 m CWT and 0.75 m CWT plots was not significantly different. The average water table levels in monocropped plots were not significantly different from intercropped plots.

Water management for the irrigation of containerized production remains a task reserved to a highly qualified personnel. Without proper instruments to determine the actual water needs, nursery crops can face growth losses of 20 to 30%. / Reviewing the different methods that are used in field production, tensiometer have shown the greatest potential of adaptation to potted plants. / Tests on the utilization of tensiometer were realized on two peat-vermiculite substrates, using two types of porous cup (1 bat--standard flow and 1 bar--high flow). The instruments were tested while permanently fixed in the growing medium, and temporarily fixed for three hours in the growing medium. / The results show that the instruments give excellent measurements for normal condition of growth, requiring saturation level between 50 and 100%, and that for both mode of operation. / Preferably, the choice of the instrument should be based on the hydraulic characteristics of the substrate. Little difference has been found using both instrument in the substrate 1, but in substrate 2 however, the high flow porous cups have given better response. The high flow cups have higher porosity and bigger pores that suit better substrate 2, which is made of coarser particles.

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Field experiments were conducted in 1996, to evaluate the need of supplemental irrigation of maize on some sandy soils in Eastern Ontario. Field and laboratory measurements of soil properties were conducted. Plow layer and deficit irrigation management approaches were evaluated. Irrigation requirements using rain and evaporation data of the humid 1996 summer, as well as data from the drier 1974 summer, were evaluated. The results show that using a root zone depth less than 300 mm led to more water losses by drainage, more irrigation water requirements and more frequent irrigation applications, as compared to using a 400 mm root zone. Therefore, it is recommended that a 400 mm root zone depth be used for scheduling irrigation applications of 25 mm. Wilting began to appear at 60% soil moisture depletion. Thus, 50% moisture depletion is suggested as the time to start irrigation to avoid crop stress. / The principal assumptions for tabulation of irrigation scheduling were: (1) That the soil is at field capacity at the beginning of June; and (2) That upward flux from a water table is negligible, since the summer water table is deeper than 2 m. These assumptions are based on the facts that rain in May keeps the soil moist, the maize is small at the end of May and that AET (Actual Evapotranspiration) is less than PET (Potential Evapotranspiration). / The measurements show that soil moisture depletion varies from site to site within the fields. The water balance was calculated using weather data and available soil moisture holding capacities for three locations on the farm. The tensions that the plant roots exerted to obtain water from the soil were measured with tensiometers and tabulated as a guide for irrigation management.

and-atmosphere interactions are an important component of climate, especially in semi-arid regions such as the Southern Great Plains. Interactions between soil moisture and vegetation modulate land-atmosphere coupling and thus represent a crucial, but not well understood climate factor. This study examines soil moisture-vegetation health interactions using both in situ observations and land surface model simulations. For the observational study, soil moisture is taken from 20 in situ Oklahoma Mesonet soil moisture observation sites, and vegetation health is represented by MODIS-derived normalized difference vegetation index (NDVI). For the modeling study, the variable infiltration capacity (VIC) hydrologic model is employed with two different vegetation parameterizations. The first is the model default vegetation parameter which is interannually-invariant leaf area index (LAI). This parameter is referred to as the control parameter. The second is MODIS-derived LAI, which captures interannual differences in vegetation health. Soil moisture simulations from both vegetation parameterizations are compared and the VIC-simulated soil moisture’s sensitivity to the vegetation parameters is also examined. Correlation results from the observation study suggest that soil moisture-vegetation interactions in Oklahoma are inconsistent, varying both in space and time. The modeling results show that using a vegetation parameterization that does not capture interannual vegetation health variability could potentially result in dry or wet biased soil moisture simulations.

Grasslands are the most important ecosystem to humanity, as they are responsible for feeding that majority of the human population. These are also very large ecosystems; they cover approximately 40% of the surface of the earth (Loveland et al., 1998), making ground-based surveys for monitoring grassland health and productivity extremely time consuming. Remote sensing has the advantage of providing reliable and repeatable observations over large swaths of land; however, optical sensors exploiting the visible and near infrared regions of electromagnetic (EM) spectrum will be unable to collect information from the ground if clouds are present (Wang et al., 2009). Imaging radar sensors, the most common being synthetic aperture radar (SAR), have the advantage of being able to image the ground even during cloudy conditions. The longer wavelengths of EM energy used by the SAR sensor are able to penetrate clouds while shorter wavelength used by optical sensors are scattered. A grassland monitoring tool based on SAR imagery would have many advantages over an optical imagery system, especially when SAR data becomes widely available. To demonstrate the feasibility of grassland monitoring using SAR, this study experimented with a set of dual-polarimetric SAR imagery to extract several grassland biophysical parameters such as soil moisture, canopy moisture, and green grass biomass over the mixed grassland in southwestern Saskatchewan. Soil moisture was derived from these images using the simple Delta Index (Thoma et al., 2006) first developed for a sparsely vegetated landscape. The Delta Index was found to explain 80% of the variation in soil moisture, in this vegetated landscape. Canopy moisture was modeled using the water cloud model (Attema and Ulaby, 1978). This model has a similar explanatory power of R2 = 0.80. This study found that only the photosynthesizing green grass biomass had a significant relationship with the canopy moisture model. However, only about 40% of the variation in green grass biomass can be explained by canopy moisture alone. The cross-polarized ratio developed from the dual polarimetric images was found to reflect the plant form diversity of the grassland. Biophysical parameters extracted from optical satellite imagery, Landsat-5 in the case of this study, were compared to those derived from the SAR images. This comparison revealed that the SAR images were superior in sensitivity to soil and canopy moisture. Optical imagery was found to be more sensitive to green canopy cover. An approach combining the results from both sensors showed an improvement in green grass biomass estimation (Adjusted R2 = 0.71).

Typescript. / Thesis (Ph. D.)--University of Hawaii at Manoa, 1984. / Bibliography: leaves [187]-199. / Microfiche. / xvii, 199 leaves, bound ill. 29 cm