Several methods of infering plant water stress for irrigation scheduling are based upon measurements of the environment in which the plants grow. These measurements include parameters such as soil water content, air temperature, pan evaporation and incident radiation. It is hypothesized that improved estimates of plant water deficit can be obtained by direct measurements made on the plants. The main objective of this study was to test the performance of measurements of canopy temperature and leaf water potential for irrigation scheduling. This study seeks to establish whether a correlation exists between these monitoring methods and measurements of soil moisture content, leaf area, and evapotranspiration. The experiments were conducted in first-year peppermint irrigated at five different rates. Canopy and air temperatures were measured with a hand-held infrared thermometer. Leaf water potential was measured with a pressure bomb. A non-stressed baseline for the difference between canopy temperature and air temperature using data from well-watered plants was used together with the vapor pressure deficit to determine the crop water stress index (CWSI). The results of this study show that the CWSI is well correlated to evapotranspiration deficit and is useful for irrigation scheduling. The relationship between leaf area yield and CWSI in peppermint was described by a quadratic function. Leaf water potential varied during the day in such a way that it was not possible to establish a relationship with water stress, differences in soil moisture content, or different irrigation levels. Leaf water potential was influenced by the daily weather conditions and represented the current demand more than the cumulative demand. The results of this study indicate that mid-day pressure bomb measurements cannot be used in irrigation scheduling. Predawn measurements of leaf water potential were stable, were well correlated with the different irrigation levels and soil moisture content, and therefore may be useful in irrigation scheduling. / Graduation date: 1993

Thesis (Ph. D.)--Washington State University, December 2008. / Title from PDF title page (viewed on Jan. 15, 2009). "The Gene and Linda Voiland School of Chemical Engineering and Bioengineering." Includes bibliographical references.

Thesis (M.S.)--Oregon State University, 2008. / Printout. Page 145 left intentionally blank. Includes bibliographical references (leaves 123-125). Also available on the World Wide Web.

The purpose of this study was to measure the influence of an ambient peppermint aroma on participants' time-on-task and performance while using FACTOR, an open-source e-Learning application. I proposed time-on-task was moderating between olfactory stimulation and performance. A 2x2 research design measured interaction of group (nonscented, scented) and gender of participants (N = 65). The learning content consisted of 28 African countries. Two methods for measuring time-on-task were employed: participant self-report at six learning intervals, and second, video recordings captured by, and stored on each participant's computer. Independent samples t tests were used to measure group and gender differences in time-on-task and performance. Relationships between time-on-task and performance were assessed using bivariate correlation and were reported as r values. Time-on-task differences between groups were not significant but garnered ES =.53. After 24 minutes of learning time, control females spent more time-on-task than control males (ES =.71), which was a statistically significant result. There was a weak to almost neutral correlation between time-on-task of all participants and performance (r =.1) where controls showed a weaker relationship (r =.05) than treatments (r =.26). The correlation between observed time-on-task and posttest performance was neutral for controls (r = .008) but moderate for treatments (r =.38). During the 40-minute learning session, the relationship between observed time-on-task and performance was r =.04 (females) and r =.55 (males), which was statistically significant. When examining time-on-task at the six measured intervals, the relationship with performance was strongest for treatments after 16 (r =.39) and 24 (r =.39) minutes of learning time. The direct influence of olfactory stimulation on performance was weak as the peppermint scent had a greater influence on time-on-task. Significant differences and notable effect sizes were not achieved by examining these variables. Analysis of the entire model showed the variables (condition, time-on-task, performance) were weakly correlated (r =.19) and that only 4% of the variance in the model was explained by its variables. As such, I failed to reject the null hypothesis, which was that time-on-task did not act as a moderator between condition and performance.

Peppermint dry weight biomass was higher in Verona (8119 kg/ha) than in Stoneville (6115 kg/ha). Overall both, oil content and yield were higher in bud formation stage than flowering stage. The levels of major essential oil constitutes were (-)-menthol 26 – 30 %, (-)-menthone 14 – 21 %, (+)-menthofuran 5 – 11 %, and eucalyptol 3 – 4 % of total essential oil content at flowering stage. Menthone content and its yield were higher at first cut; however, (+)-menthofuran content and its yield were higher at the second cut at bud formation. Although N fertilizers at rate 80 kg/ha did not affect essential oil content and yield at cut 1, N rate at 80 + 80 kg/ha increased oil yield at cut 2.

The efficiencies of wet sieving/sucrose centrifugation (WS/SC) recovery of Pratylenchus penetrans (59 %), Paratylenchus sp., (80 %), and Criconemella xenoplax (66 %) were established. Baermann funnels (BF) recovered significantly more P. penetrans (p = 0.01) and significantly less (p = 0.01) C. xenoplax than did WS/SC. While densities of P. penetrans in stored soil remained constant over the three days following field sample collection, Paratylenchus sp. and C. xenoplax densities increased significantly on the second day and decreased to their original level on the third day. During mist chamber extraction, P. penetrans continued to emerge from peppermint root tissue for 38 days, but 90 % of the total was recovered after 10 days. The standard core, consisting of 500 g dry soil plus the roots and rhizomes in that soil, was developed to express endoparasitic and ectoparasitic nematode densities in peppermint field soil, roots, and rhizomes. Enumerating nematode densities within the different plantsoil components of a particular volume of soil more closely describes the total nematode population pressure on the plant growing in that volume of soil. Therefore, endoparasitic nematode population levels were expressed as numbers in standard core soil, roots, rhizomes, or total core (soil, root, and rhizome populations combined). P. penetrans populations in peppermint fields peaked in early May, decreased through the summer, peaked again in August, and decreased through the fall to a low winter level. Peaks in the P. penetrans population followed peppermint root weight peaks by 3 to 6 wks. Paratylenchus sp. populations remained at relatively low levels throughout the year except for a pronounced peak in August, which followed the root weight peak by 3 to 6 wks. The C. xenoplax population also peaked 3 to 6 wks after the August root weight peak but fluctuated markedly throughout the remainder of the year. From 70 to 90 % of the total P. penetrans population was in roots in early May, decreased to 40 to 50 % by late June and 20 to 40 % in August. Up to 20 % of the population was in rhizomes on some dates, but the rhizome percentage was usually less than 10. Fewer P. penetrans were recovered from rhizomes during the harsh winter of 1988-89 than during the mild winter of 1989-90. Analysis of point samples (pretreatment, posttreatment, and harvest samples) and area under nematode population curves (AUNPC) were used to compare nematode populations in oxamyl-treated (1.1 kg a.i./ha) and nontreated plots in two peppermint fields through the two growing seasons. Point sample analyses detected significant decreases in treated soil, root, and total standard core P. benetrans populations compared to nontreated populations in several pretreatment and harvest sample dates and in two rhizome harvest sample dates. No treatment differences were observed in Paratylenchus sp. or C. xenoplax populations using this analysis. AUNPC analysis detected significant decreases in several treated root and rhizome P. penetrans populations compared to nontreated populations and in total core populations in field 1 during one growing season and in field 2 during two growing seasons. Significant decreases in C. xenoplax populations were observed in one field during one growing season. Peppermint hay weight was significantly greater in treated than in nontreated plots in one of three fields in 1988 and in one of three fields during 1989. Oil in ml/kg fresh hay weight was significantly lower in treated than in nontreated plots in one of three fields during 1989. No treatment differences were detected in milliliters of oil distilled from 2m² field area. Peppermint oil production is the final measure of a treatment from a mint grower's perspective. Because oxamyl had no effect on mint oil production, AUNPC appears to be a better measure of parasitic nematode pressure on peppermint, since this method of analysis detected fewer significant differences between nematode populations between treated and non-treated plots. / Graduation date: 1991

Two experiments were conducted to examine the use of peppermint leaves and cinnamon oil on methane production and apparent ruminal digestibility. In experiment 1, 12 jars were utilized in a completely randomized design to conduct three separate 24 hour batch culture experiments. The objective of the batch culture experiments was to examine the effects of the selected natural supplements on methane production. For the first batch culture, jars were randomly assigned to one of the following treatments: 1) control diet (CON); 2) CON plus the addition of peppermint leaves at 3% of the diet (PEP3); 3) CON plus the addition of peppermint leaves at 6% of the diet (PEP6); or 4) CON plus the addition of peppermint leaves at 12% of the diet (PEP12). The addition of the peppermint leaves increased (P = 0.004) oxygen and tended to increase (P = 0.10) nitrogen gas, but had no significant (P ≥ 0.15) effect on methane production. For the second batch culture, jars were randomly assigned to one of the folloiwng treatments: 1) control diet (CON); 2) CON plus the addition of cinnamon oil at 125 mg/L (CIN 125); 3) CON plus the addition of cinnamon oil at 250 mg/L (CIN250); or 4) CON plus the addition of cinnamon oil at 500 mg/L (CIN500). Cinnamon oil decreased (P = 0.002) methane production when added at 500 mg/L which also decreased (P = 0.001) total gas production compared to the other treatments. For the final batch culture, jars were randomly assigned to one of the following treatments: 1) control diet (CON); 2) CON plus the addition of peppermint leaves at 3% of the diet and cinnamon oil at 125 mg/L (3:125); 3) CON plus the addition of peppermint leaves at 3% of the diet and cinnamon oil at 250 mg/L (3:250); or 4) CON plus the addition of peppermint leaves at 6% of the diet and cinnamon oil at 125 mg/L (6:125). The addition of the peppermint leaves at 6% of the diet and cinnamon oil at 125 mg/L significantly decreased nitrogen (P = 0.05) and methane (P = 0.0001) gas production compared to CON and 3:250 treatment. Based on the results of the three batch cultures, experiment 2 utilized four dual-flow continuous fermenters in a Latin Square design to examine the effects of the selected natural supplements on apparent ruminal digestibility and ruminal characteristics. Fermenters were randomly assigned to one of the following treatments: 1) control diet (CON); 2) CON plus the addition of peppermint leaves at 3% of the diet (PEP3); 3) CON plus the addition of cinnamon oil at 500 mg/L (CIN500); or 4) CON plus the addition of peppermint leaves at 6% of the diet and cinnamon oil at 125 mg/L (COMBO). Treatments for experiment 2 had no effect (P ≥ 0.17) on apparent ruminal digestibility of nutrients. There was no significant difference (P ≥ 0.09) in total or individual VFA concentrations, suggesting that the use of peppermint leaves, cinnamon oil, or a combination of the two has no adverse effects on apparent ruminal digestibility. Feeding ruminants a natural supplement such as cinnamon oil, peppermint leaves, or a combination could potentially reduce GHG production when feeding a low-quality, forage based diet.

Graduation date: 1995

No description available.

The agricultural production of peppermint has been shown to contribute significant quantities of nitrate-nitrogen to groundwater recharge. In an effort to provide new tools for increasing nitrogen efficiency within peppermint production, three research questions were proposed: i) How should plant tissue samples be collected to achieve the greatest precision when using the mint stem nitrate test for nitrogen management?; ii) What is the consumptive use of water by peppermint in the post-harvest period?; and iii) How does irrigation uniformity affect nitrate loading to groundwater when N is supplied through chemigation? In the first investigation, structured field experiments were designed and conducted on commercial peppermint fields to isolate potential environmental, management, and sampling influences on stem nitrate test results. The most significant effects observed were those of the type of stem material collected (a 441% effect at p<0.001) and the number of stems collected to estimate the field mean concentration. It was found that the variance of the sample population and the number of stems required for a given sampling error could be greatly reduced by only collecting stems from within the plant canopy. Less pronounced but statistically significant differences in stem nitrate concentrations were produced by variations in solar radiation on hourly (a 17% effect at p<0.05) and daily (a 29% effect at p<0.01) scales. In an analysis of stem nitrate spatial variability, a purely random distribution of stem nitrate concentrations was observed on the 1-150 m scale. For the second investigation, a field study was conducted to measure the consumptive use of peppermint in the post-harvest period and to develop crop coefficients (Kc) used to predict evapotranspiration rates. The soil water balance was measured on two fields with a neutron moisture probe over an 80 day period. Over the 49 days following harvest, a cumulative consumptive use of 96 mm was observed. Basal crop coefficients increased from near zero to approximately 0.40 within 40 days post-harvest. The third, and final, investigation developed a simple heuristic statistical model to explore the effective adequacy of chemical application as influenced by the uniformity of irrigation. To perform this analysis, an expression was presented whereby irrigation distribution parameters for the normal, or Gaussian, model could be derived from common irrigation design terms. The results of this model indicate that the effective chemical adequacy is greatly compromised when the irrigation uniformity coefficient is low and/or the design irrigation adequacy is high. / Graduation date: 1998