Thesis (Ph.D.)--Murdoch University, 2008. / Thesis submitted to the Faculty of Sustainability, Environmental and Life Sciences. Includes bibliographical references (leaves 147-163)

The Linear Voltage Differential Transformer (LVDT) is an accurate sensor for stem diameter measurements. Based on the results of this dissertation it was found that stem diameter [mm] was related to water content [grams] of the cotton crop by the following equation: W(D) = 0.114(D)³ˑ¹⁸² Also the ratio of stem diameter contraction rate to the rate of water loss in cotton was experimentally determined to be: (dW/dt)/(dD/dt) = (0.166 [g min⁻¹])/(0.535 [μm min⁻¹]) = (.0469% per minute)/(.0039% per minute). Similarly the cellular water potential was derived to be a non linear function of stem diameter in cotton: ψ(t) - ψₒ = 2 ε ln (D(t)/ Dₒ) + πₒDₒ² [(1/D²(t)) – (1/Dₒ²)]. Based on this work, the grower can estimate the water content, transpiration rate and water potential of the cotton crops via stem diameter measurements. Moreover, a computer system can be implemented to remotely keep track of the water status of the field, and control the irrigation system. A general model was proposed to quantify the nature of input-output relation of the cotton crop. A proposed simplified model based on stem diameter is also introduced. The stem diameter measurements can be used as an index for estimation of cotton's water content, transpiration rate, and water potential. These three parameters and the proposed simplified model established a plant based predictive irrigation scheduling technique. The electrical output of the LVDT was quite noisy. To remove the noise and demodulate the data, two cascade circuits were designed and implemented. First, the external output circuit removed the noise and isolated the LVDT. Second, the LVDT signal conditioner demodulated the phase information from the secondary windings which were produced by the movement of the rod. By the implementation of these circuits, 1 m of the rod displacement resulted in 1.14 mv of dc voltage changes in the output.

Mémoire (M.Ress.Renouv.)--Université du Québec à Chicoutimi, 1999. / Document électronique également accessible en format PDF. CaQCU

Thesis (Ph. D.)--University of Missouri-Columbia, 1999. / Typescript. Vita. Includes bibliographical references (leaves 93-96). Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 1999. / Typescript. Vita. Includes bibliographical references (leaves 93-96). Also available on the Internet.

Thesis (M.S.)--University of Wisconsin--Madison, 1981. / Typescript. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 94-96).

The study of readily measurable agronomic traits which may estimate total dry matter production and the determination of their relationships with quality characteristics needs more emphasis in alfalfa breeding. The main objective of this study was the selection of specific stem weight (SSW) and its relationship to other agronomic and nutritive traits. A secondary study was on agronomic and nutritive traits and their relationship with one another. Means, standard deviations, analyses of variance, and correlations were obtained on 98 Mesa-Sirsa alfalfa clones for SSW, plant height, yield, leaf-stem ratio, stem acid detergent fiber (ADF), leaf ADF, stem acid detergent lignin (ADL), and leaf ADL. The means of SSW (70-47 mg/5 cm), plant height (58-48 cm), yield (52-23 g), leaf-stem ratio (2.1-1.0), stem ADF (45-42%), and stem ADL (10.1-9.1%) varied from one harvest to another depending on the temperature. Significant differences were observed among alfalfa clones on June 1980 for SSW, plant height, yield, leaf-stem ratio, stem ADF, stem ADL, and leaf ADL. Range values were as follows: SSW (92-53 mg/5 cm), plant height (70-41 cm), yield (82-22 g), leaf-stem ratio (1.6-0.6), stem ADF (50-36%) stem ADL (13-8%), leaf ADF (18-13%), and leaf ADL (5-3%). A low correlation was reported between stem ADF and SSW (0.34) and also was observed between stem ADF and leaf ADF (0.46). The SSW probably would be more effective in increasing total dry matter production in dense stands. The coarseness of the stem was not related with high fiber. High leaf ADF could be useful in selecting for leaf cells which are more resistant to rupture and would gradually release soluble protein in the rumen; thus, the incidence of bloat probably would be reduced. A low stem ADF would make the stem more digestible; therefore, intake of the stem fraction may be greater. With more coarse material in the rumen, salivary secretion might be stimulated. The SSW and stem ADF could be used to select individual genotypes which could increase growth and development and at the same time improve forage quality, since SSW and stem ADF are not related.

Plants under variable water stress exhibit a contraction of their stem diameter. This variation can be monitored to determine the plant water status which, in turn, will lead us to a method of scheduling subsequent irrigation. In this dissertation, the possibility of determining the water status in cotton plants by automatically sensing their stem diameter variation was explored. A full description of the displacement sensor, the electronic circuits used for automatic stem diameter monitoring and the data analysis is given. Simultaneous measurement of the leaf water potential and the stem diameter variation were done for a total of eight days during an irrigation cycle. Statistical analysis was performed to infer the water status in the plant from the stem diameter variation. It was discovered that the stem diameter variation lags the water potential by two hours, and that there was no simple linear correlation between them. In fact, it was discovered that the stem diameter variation was not only a function of the leaf water potential of the plant as it was believed; but indeed, it is also a function of the soil water condition. According to the results obtained, a basic model to describe the relationship between the stem diameter variation and the plant and soil water condition was developed.

No description available.

Thesis (Ph. D.)--University of Missouri-Columbia, 2001. / Typescript. Vita. Includes bibliographical references (leaves 143-149). Also available on the Internet.