Ground-based, remotely sensed reflectance and temperature data were collected over differentially irrigated, developing cotton and sorghum canopies in order to investigate interrelations of these parameters; to monitor their temporal changes ; to understand their spatial structure ; and to estimate crop coefficient (KO from canopy reflectance. Spectral reflectance and derived vegetation indices showed ability to significantly discriminate among differential irrigation levels of sorghum canopies, starting the fourth week of growth. All vegetation indices increased as a result of crop development, with the perpendicular vegetation index (PVI ) demonstrating the greatest potential for assessing water stress conditions, whereas, soil indices behaved independently of crop development and water stress. Canopy temperature and derived water stress indices, on the other hand, were in high concordance and were able to detect crop water stress with variable degrees of sensitivity. Experimental variograms revealed that cotton reflectance and temperature were not spatially dependent when all water treatments were included. For the moisture stress treatments, only canopy temperature exhibited spatial dependence early in the period of stress. Sorghum canopy reflectance and temperature demonstrated some spatial structure; however, a drift was suspected due to regularity in the data spatial distribution. Normalized difference (ND), normalized perpendicular vegetation index (NPVI) and normalized green vegetation index (NGVI), for fifty days covering the period from planting to heading, were fitted with a complementary error function equation with minor adjustment. Both NPVI and NGVI displayed a 1:1 relation with interpolated tabular values of basal Kc, whereas ND deviated from the 1:1 relation for the period beyond 30 days after planting. The model was also found to be valid for estimating K(c) for moderately deficit irrigation conditions.

No description available.

No description available.

Carbon and energy fluxes were measured with the eddy covariance technique above two semi-arid ecosystems, ponderosa pine and juniper/sagebrush, located in central Oregon. The two ecosystems have low LAI and a very open canopy structure. The energy closure was ~70-80% at both ecosystems, equivalent to an imbalance of 150-250 W m⁻² on cloudless summer days, when net radiation (R[subscript n]) was ~600-700 W m⁻². The lack of closure cannot be explained by the uncertainty of an estimate of available energy due to a single R[subscript n] sensor location. At the more open juniper/sagebrush ecosystem, a numerical model showed that spatial variation in R[subscript n], even for large differences in surface radiation temperature and reflection coefficient between ecosystem components (soil and vegetation), is less than 10% of measured R[subscript n]. The uncertainty in R[subscript n] at the two-layered ponderosa pine ecosystem with patches of young and old-growth trees is expected to be smaller than at the juniper ecosystem. Net carbon exchange (NEE) at the pine site strongly depends on environmental factors effecting carbon assimilation (A[subscript c]) and ecosystem respiration (R[subscript e]). A more detailed analysis of the carbon budget showed a strong negative response of carbon uptake to large vapor pressure deficits (VPD), whereas water vapor exchange (LE) was less affected. At large VPD the vegetation maintains a sustainable water flow through the soil-plant system by stomatal control of transpiration. The stomatal closure leads to limitation in A[subscript c], but LE is subject to a positive feedback from higher evaporative demand. Annual NEE of the ponderosa pine forest (200-300 gC m⁻²) was in the mid-range of reported NEE of temperate forest ecosystems, though, unusually, much of the annual carbon gain occurred during the fall through spring, because the relatively mild winters allowed carbon assimilation to occur and R[subscript e] rates were low. The information gathered at our ponderosa pine site during two years with contrasting climate suggests that the carbon uptake of the ponderosa pine ecosystem will be more sensitive to global climate change than the water vapor exchange. / Graduation date: 2000

Thesis (M.S.)--University of Missouri-Columbia, 2003. / Typescript. Includes bibliographical references (leaves 61-63). Also available on the Internet.

Thesis (M.S.)--University of Missouri-Columbia, 2003. / Typescript. Includes bibliographical references (leaves 61-63). Also available on the Internet.

The West African savanna is characterized by limited and erratic rainfall in one rainy season, increasing degradation of plant and soil resources, a rapidly growing population, and annual food shortages. Zorse is a Kusasi village in Bawku District, Upper Region, northeast Ghana. The Kusasis are intensive farmers of millet and sorghum who live in villages of houses dispersed over the savanna. Surrounding each house is the continuously cultivated field called the saman whose fertility is maintained by annual applications of manure and compost. Field work in Zorse from October, 1978, to March, 1978, included an intensive study of a 50% sample of all houses in the village (n = 126) containing 900 people. In the traditional farming system each household grows and consumes its food as a unit. During the wet season there is a high demand for labor, especially for weeding, but food supplies are at an annual low. In the dry season farming activity is limited to those with dry season gardens. Agricultural development began in earnest in the 1930's but annual food shortages continue to worsen and famine, such as the one in 1976-77 has not been uncommon. Population growth and structure is determined by fertility, mortality, and migration, and reflects the population's relationship to its environment. Population pyramids for Zorse are like those for other areas of the savanna. Their broad bases reflect high mortality and fertility and their skewed sex ratios are the result of excessive outmigration by males 15-45 years old. Migration has been increasing since the beginning of the century and presently about 50% of males 15-45 years old are absent from Zorse and the Upper Region for extended periods of time. Fertility has also been increasing, primarily as a result of decreasing birth intervals, but also as a result of decreasing age at marriage. Birth intervals are controlled by postpartum sexual abstinence. Kusasi couples make the decision to resume intercourse based on the health and development of the youngest child. The shortening of birth intervals reflects the decreased mortality and increased personal security. The pace of social change has increased greatly since the establishment of the British in 1900. The endemic warfare and feuding were stopped and personal security was greatly increased. Public health programs and Western medical treatment were introduced and links with the rest of Ghana and the world were established and began to grow. The savanna environment is fragile and agriculture in Bawku depends on highly variable rainfall of about 1000 mm per year, and on maintaining fertility on the thin, erosion-prone soils. In areas of high population density like Bawku, there is much evidence of soil erosion, loss of soil structure and fertility, and degraded vegetation. The rapid population growth and high emigration rate in Bawku and similar areas of the savanna jeopardize the possibility of improving the food supply. People's decisions about migrating and birth spacing are adaptations to an intensive agricultural system in an environment where productive potential is decreasing under the present system. For the situation to improve it will be necessary for community resources management systems to develop so that demographic and farming behavior by individuals and households will be linked to community well being.

A Handbook Prepared by The University of Arizona for the City of Tucson.

Thesis (PhD)--University of South Australia, 1998

88 leaves : ill., maps, tables, photos. (part col.) ; 30 cm. / Title page, contents and abstract only. The complete thesis in print form is available from the University Library. / Thesis (Ph.D.1976) from the Dept. of Botany, University of Adelaide