No description available.

Switchgrass (Panicum virgatum L.), a warm-season grass, grows most rapidly in mid-summer when cool-season species such as tall fescue (Festuca arundinacea Schreb.) may have limited growth due to high temperature and low soil moisture availability. The objectives of this study were to investigate physiological factors and to determine management strategies that could optimize growth of switchgrass. The influences of two successive drought cycles on performance and water relation parameters of switchgrass and tall fescue were studied in growth chamber conditions. Water was withheld from conditioned plants until elongation of tillers stopped. Then pots were rewatered and a new drought cycle followed. Control plants remained well watered during this time. Both conditioned and control plants were then subjected to a challenge water stress. Total leaf elongation and soil water content (SWC) were measured daily. Leaf water potential (Ψ), osmotic potential (Π), relative water content, and concentrations of K, Na, Ca, and total free sugars were measured at the end of each water-stress cycle. Osmotic potential at full turgor (Π₁₀₀), symplastic water content (SYM) , and modulus of elasticity (∊) were determined from pressure-volume curves at the end of the two conditioning cycles. Conditioned plants of both species elongated more during the challenge water-stress than control plants and had lower SWC and Ψ when their leaf elongation ceased. Conditioned plants exhibited osmotic adjustment, accumulating free sugars and K, as a result of drought stress. Switchgrass SYM did not change, while Π₁₀₀ decreased, suggesting active salt accumulation. Increased ∊ somewhat counteracted the beneficial influence of osmotic adjustment. Tall fescue SYM increased, while Π₁₀₀ did not change. Decreased ∊ improved drought tolerance of tall fescue. Field experiments were conducted to investigate the influence of date of first harvest and cutting height on yield distribution and canopy characteristics of ‘Pathfinder’ (2-yr study), ‘Cave-in-rock’, and ‘Blackwell’ (1-yr study) switchgrass. Seasonal distribution of dry matter production was established by measuring first-harvest yields and regrowth. The canopy of Pathfinder was characterized by determining number and weight of tillers, light penetration, leafiness, specific leaf weight, and leaf area index in profiles of the canopy before harvest and in regrowth. First-harvest yields increased as date of first cut was delayed and cutting height was lowered. Cutting at 20 cm decreased the yield of first cutting in a second growing season. Plots not harvested in the first growing season gave higher yields in the second growing season compared with previously harvested plots, suggesting that any harvest may decrease subsequent yield potential. Regrowth decreased as date of first cut was delayed. A cutting height of 30 cm produced greater regrowth than cutting at 20 cm. Yields and canopy characteristics suggest that removal of growing points decreased second-harvest yields and weakened regrowth potential in the following year. To maximize regrowth to be used for grazing during July and August, switchgrass hay should be cut after 10 June and before 21 June. / Ph. D.

Soil moisture tension had a greater effect on both soil surface temperatures and growth of young Kentucky 31 tall fescue (Festuca arundinacea) seedlings under solar radiation than either wood-cellulose mulch or slope-facing. More growth and lower temperatures occurred at low than high moisture tensions. Mulch did not consistently benefit growth. Slope effects were evident primarily at high tensions: higher temperatures and less growth occurred on south than north slopes. Temperatures (a) within a millimeter above the soil-air interface and (b) below the surface of, yet within the mulch layer seemed the most critical to seedling growth. Inadequate moisture control, a sparse seeding rate, a high mulching rate, and below optimal weather conditions complicated environmental control and produced some ambiguous results. A characterization of surface temperature injury to perennial ryegrass (Lolium perenne) seedlings grown with wood-cellulose mulch at two moisture tensions showed seedling injury to increase with surface temperature while air and soil temperatures had no significant effect. Low moisture tension produced lower surface temperatures and less injury than high tension. / M.S.

M.S.

No description available.

No description available.

Diverse forage mixtures have improved resilience to drought, improved persistence, ability to adapt to changing environmental conditions, reduced fertilizer costs, improved root mass and greater soil carbon sequestration but do they improve forage and animal production. The objective was to determine if complex native forage mixtures provide superior nutritional quality throughout the grazing season as compared to simple native mixtures. Three studies were conducted in 2007 at Swift Current, SK to evaluate forage production potentials, nutritive qualities and in vitro dry matter digestibility of native and tame forage species common to or having potential in Southwestern Saskatchewan. In study one, plots were seeded in 2006 on Chernozemic Orthic Brown Swinton Loam soils and consisted of 11 native and three tame monoculture species common to southwestern Saskatchewan. Clippings at a 5 cm stubble height occurred on June 20 and every 28 days after until October 10. Forage DM production, in vitro OMD, NDF, ADF, ADL, CP, Ca and P concentrations were measured. As species matured, production and OMD declined (P¡Ü0.05) but NDF, ADF and ADL concentrations increased (P¡Ü0.05). There were harvest date by species differences (P¡Ü0.05) in forage production and nutritional qualities of C3 and C4 grass and legume species. Study two examined the in situ CP, NDF and DM disappearance of six selected species harvested in the fall. EDNDF and ADDM values did not differ (P>0.05) among C3 grasses. The C4 grasses had higher (P<0.05) EDNDF and EDDM and the legume, Canadian milkvetch had the highest (P<0.05) EDDM but lowest EDNDF. Study three occurred in 2005, 2006 and 2007 to determine if complex native forage mixtures had superior forage and animal production as compared to simple forage stands. Grazing occurred from June through August to achieve 60% utilization. Animal weights and available, cage and residual forage yields were taken to determine production and utilization. Forage production and quality did not differ (P>0.05) between simple and complex forage mixtures but animal production (AUD ha-1) was higher on complex native mixtures. Overall results showed; 1) C3 and C4 grass and legume species have different growth patterns and qualities that can improve forage quality and degradability of the stand throughout the grazing season, 2) forage and animal production benefits associated with complex native forage mixtures largely depend on environmental conditions like temperature and moisture.

Diverse forage mixtures have improved resilience to drought, improved persistence, ability to adapt to changing environmental conditions, reduced fertilizer costs, improved root mass and greater soil carbon sequestration but do they improve forage and animal production. The objective was to determine if complex native forage mixtures provide superior nutritional quality throughout the grazing season as compared to simple native mixtures. Three studies were conducted in 2007 at Swift Current, SK to evaluate forage production potentials, nutritive qualities and in vitro dry matter digestibility of native and tame forage species common to or having potential in Southwestern Saskatchewan. In study one, plots were seeded in 2006 on Chernozemic Orthic Brown Swinton Loam soils and consisted of 11 native and three tame monoculture species common to southwestern Saskatchewan. Clippings at a 5 cm stubble height occurred on June 20 and every 28 days after until October 10. Forage DM production, in vitro OMD, NDF, ADF, ADL, CP, Ca and P concentrations were measured. As species matured, production and OMD declined (P¡Ü0.05) but NDF, ADF and ADL concentrations increased (P¡Ü0.05). There were harvest date by species differences (P¡Ü0.05) in forage production and nutritional qualities of C3 and C4 grass and legume species. Study two examined the in situ CP, NDF and DM disappearance of six selected species harvested in the fall. EDNDF and ADDM values did not differ (P>0.05) among C3 grasses. The C4 grasses had higher (P<0.05) EDNDF and EDDM and the legume, Canadian milkvetch had the highest (P<0.05) EDDM but lowest EDNDF. Study three occurred in 2005, 2006 and 2007 to determine if complex native forage mixtures had superior forage and animal production as compared to simple forage stands. Grazing occurred from June through August to achieve 60% utilization. Animal weights and available, cage and residual forage yields were taken to determine production and utilization. Forage production and quality did not differ (P>0.05) between simple and complex forage mixtures but animal production (AUD ha-1) was higher on complex native mixtures. Overall results showed; 1) C3 and C4 grass and legume species have different growth patterns and qualities that can improve forage quality and degradability of the stand throughout the grazing season, 2) forage and animal production benefits associated with complex native forage mixtures largely depend on environmental conditions like temperature and moisture.

Thesis (M.S.)--Oregon State University, 2010. / Printout. Includes bibliographical references (leaves 31-39). Also available on the World Wide Web.

Global climate change is expected to be accompanied by changes in the composition of plant functional types. Such changes are predicted to follow shifts in the percentage cover and abundance of grass species, following the C3 and C4 photosynthetic pathways. These two groups differ in a number of physiological, structural and biochemical aspects. It is important to measure these characteristic properties because they affect ecosystem processes, such as nutrient cycling. High spectral and spatial resolution remote sensing systems have been proven to offer data, which can be used to accurately detect, classify and map plant species. The major challenge, however, is that the spectral reflectance data obtained over many narrow contiguous channels (i.e. hyperspectral data) represent multiple classes that are often mixed for a limited training-sample size. This is commonly referred to as the Hughes phenomenon or “the curse of dimensionality”. In the context of hyperspectral data analysis, the Hughes phenomenon often introduces a high degree of multicollinearity, which is caused by the use of highly-correlated spectral predictors. Multicollinearity is a prominent problem in processing hyperspectral data for vegetation applications, due to similarities in the spectral reflectance properties of biophysical and biochemical attributes. This study explored an innovative method to solve the problems associated with spectral dimensionality and the related multicollinearity, by developing a user-defined inter-band correlation filter function to resample hyperspectral data. The proposed resampling technique convolves the spectral dependence information between a chosen band-centre and its shorter and longer wavelength neighbours. The utility of the new resampling technique was assessed for discriminating C3 (Festuca costata) and C4 (Themeda triandra and Rendlia altera) grasses and for predicting their nutrient content (nitrogen, protein, moisture, and fibre), using partial least squares and random forest regressions. In general, results obtained showed that the user-defined inter-band correlation filter technique can mitigate the problem of multicollinearity in both classification and regression analyses. Wavebands in the shortwave infrared region were found to be very important in regression and classification analyses, using field spectra-only datasets. Next, the analyses were up-scaled from field spectra to the new generation multispectral satellite, WorldView-2 imagery, which was acquired for the Cathedral Peak region of the Drakensberg Mountains. The results obtained, showed that the WV2 image data contain useful information for classifying the C3 and C4 grasses and for predicting variability in their nitrogen and fibre concentrations. This study makes a contribution by developing a user-defined inter-band correlation filter to resample hyperspectral data, and thereby mitigating the high dimensionality and multicollinearity problems, in remote sensing applications involving C3 and C4 grass species or communities. / Thesis (Ph.D.)-University of KwaZulu-Natal, Durban, 2013.