The adverse effect of moisture stress at flowering and maturation stages on corn (Zea mays L.) grain yield is well documented. Stress at vegetative stages, on the other hand, affects dry matter more than grain yield but is also reported to condition the corn plant to withstand later stress. The objectives of this study were (1) to determine if moisture stress at vegetative stages could condition the corn crop to minimize the effect of stress at reproductive stages, and (2) to document the effect of this vegetative stress on corn root growth, water use and yield. Secondary root initiation was reduced by moisture stress at the 4 and 7 leaf stages. Moisture stress during vegetative stages reduced water use and stover weight but not grain yield. However, stress at silking reduced grain yield. Stress at vegetative stages did not precondition the corn to endure water deficit later in the season.

A field experiment was conducted to evaluate the effect of planting date on Upland as a short staple (Gossypium hirsutum L.) and Pima cotton as a long staple (Gossypium barbadense L.) cotton. Planting dates were 27 April, 13 May, 27 May, and 9 June, 1988. Cotton varieties consisted of three maturity groups: early maturity Delta and Pine Land 20 (DPL 20) and full season Delta and Pine Land 90 (DPL 90) from G. hirsutum L., and Pima S-6, a variety of the more indeterminate type G. barbadense L. A number of cold periods at Marana in the early spring of 1988 created unfavorable conditions for all cotton varieties on the early planting date. This condition resulted in lower head unit (H.U.) availability during germination, and significantly altered the usual pattern for flowering on planting date (PD) 1. The amount of H.U. accumulation for PD 2, especially during germination, was higher than for PD 1. (Abstract shortened with permission of author.)

A greenhouse experiment was conducted to evaluate the effect of five amendments (H₂SO₄, Al₂(SO₄.18H₂O, FeSO₄.7H₂O, and CaS₅ and CaSO₄.2H₂O) on crust formation, seedling emergence, dry matter yield (DMY) of tomato and soil properties in a sodic soil from the Safford Agricultural Center. When applied in equivalent quantities (600 kg/ha S), sulfuric acid and Al-sulfate proved to be the best anti-crusting agents and gypsum the least. Tomato seedling emergence and DMY increased with addition of H₂SO₄ followed by gypsum. Sulfuric acid was superior in reducing ESP in 0-3 cm depth, while EC was increased with additions of all amendments. In 3-8 cm depth the amendments affected pH, EC and ESP less than at the 0-3 cm depth. DTPA extractable and plants concentrations of Zn, Fe and Mn significantly increased with the addition of various amendments, while Cu was not effected by any amendments.

Crop performance depends on genotype, the environment in which the crop is grown, and interaction between genotype and environment. A measure of these effects is important in determining adaptation and in recommending crop genotypes to growers. In instances where hybrid seed has been introduced into developing countries, which often traditionally save seed for the next planting, determining the adaptation of genotypes and making accurate recomendations may be difficult. This experiment evaluated 15 commercial hybrid grain sorghums (Sorghum bicolor (L.) Moench), along with their segregating F₂ and F₃ generations, for adaptation to variable moisture environments. Grain yield per entry in all tests was the main phenotypic character used to measure adaptation in environments differing in mean moisture stress. Grain yield was also the main characteristic used to observe changes through generations F₁ to F₃.There was an expected decrease in yield with decreased irrigation, and with advanced generations. A close association was observed between mean 3-year grain yield of the selected hybrids and their F₂ and F₃ progenies when grown in the same environment.

Greenhouse studies were carried out to determine the effects of three calcareous soils on the foliar growth and elemental composition of a vinifera variety, three common roostocks, and the variety grafted to the three roostocks. Soils, water, shoot growth, tissue analyses, and cation uptake were evaluated in grapevines on which grape variety rootstocks and grafted materials were established on Mohall, Sonoita, and Casa Grande soil series in PVC columns collected from three agricultural areas in Arizona. Grapevines have a root system that explores the subsoil as well the surface of the soil; however, in calcareous soils with high pH and high lime content, some micronutrient are relatively insoluble, also calcium tends to be precipitated forming calcium carbonate and becomes water insoluble; therefore, the purpose of this study is to evaluate the roostock effect in the nutritional uptake. Good compatibility was observed between rootstocks and scions, also all grafted vines grew very well and no chlorosis or foliar elemental deficiencies were obserbed during the experiments. In this study, roostocks showed bigger shoot growth in grapevines than the rest of the treatments. Grafted grapevines contained higher foliar potassium than the rest of the treatments. Also all material evaluated had calcium and iron deficiencies with content less than 1.2 percent and 70 mg kg-1, respectively, and no one had more than 0.5 percent of sodium content, foliar grape content reported by California that can be a problem. Cabernet savignon had the highest magnesium content in the three soils. Cation balance was used to measure the cation uptake for the evaluated materials; consequently, grafted plants had higher cation uptake than nongrafted plants. In this evaluation, Cabernet savignon grafted to 41 B had the highest cation content in comparision with every treatment; therefore, it was the highest in potassium, calcium, magnesium, and iron content. No one treatment had a deficient level of manganese; although, the studied soils were basic with high pH. In relationship with copper uptake, Dogridge had the highest copper uptake in the three evaluated soils.

Increased efficiency in agricultural production is becoming increasingly important in the present economic climate. The three studies presented in this dissertation have been developed to help producers achieve a greater efficiency with respect to crop production. The first is the development of the cotton monitoring system (CMS). This software was developed as an end product to over ten years of research into cotton crop monitoring. It allows for the entry of crop growth and development data, along with other crop inputs. All growth indices are plotted against long-term baselines to indicate the crops status in relation to normal growth patterns. Other University of Arizona extension publications are available that are directed at helping the user interpret the data and how best to use it in making management decisions. The second project involves the evaluation of added nitrogen interaction (ANI) effects in irrigated cotton. This was accomplished by comparing two methods of determining nitrogen recovery efficiencies (NREs), the difference technique and the isotopic dilution technique. No differences were observed between the two methods in the first year, 1997 indicating the absence of a ANI. However in 1999, differences were observed between the two methods due to abnormally high vegetative growth experienced by the crop which resulted in increased root growth and subsequent exploration of the soil and an increased uptake of soil N. The third and final project was conducted to examine the loss of N from several different sources of irrigation water around the state of Arizona and to observe the effects of temperature on this process (25, 30, 35, and 40°C). Ammonium sulfate was added to a 350 mL volume of water from which aliquots were drawn at specific time intervals and analyzed for NH₄⁺-N. In a 24 hour period up to 90% of the added N was lost at 40°C). In general, as soluble salts increased the rate at which NH3 was volatilized also increased. The results from this study indicate the need to consider potential N losses from irrigation water when making decisions regarding N fertilizer management.

This research evaluated flow characteristics in three irrigation system components: Venturi injector, chemigation oil drop generator, and pressurized landscape bubbler. Foliar chemicals are often applied as oils through irrigation systems in order to prevent wash off from leaves. The system application uniformity and efficiency depends on oil drop size distribution. The primary parameters that influence oil drop size are water flow rate and eddy shear stress, interfacial tension and oil viscosity. In this laboratory experiment, the oil-based chemical drop diameter distributions were evaluated over a range of these physical parameters. Drop sizes were in the range of an equation used to predict drop size in turbulent flow; however, there was very little change in drop size with change in physical parameters. The injection flow rate for four chemicals (CAN17, UAN32, soybean oil, and OrchexRTM) and water was measured over a range of pressure differentials between the upstream and downstream side of the Venturi, and over a range of chemical temperatures. The injection flow rate for water, with low viscosity, did not change significantly with temperature. However, the injection rate for the four chemicals was correlated with temperature and viscosity. If the chemical tank temperature variation is 20°C during the day, then the injection flow rate variation would be in the range of 50% for soybean oil, 30% for OrchexRTM, 10% for UAN32, and 5% for CAN17. Five commercial bubbler with flow rate screw adjustments were evaluated: RainbirdRTM, ToroRTM, IrritrolRTM , HunterRTM, and LegoRTM. The coefficient of variation at full flow for the five brands ranged from 8.2% to 20.8%. Bubbler flow rates were measured at 140 and 210 kPa over a range of number of screw turns. Equations were developed for each bubbler based on the emitter flow equation, Q = KHx. Because K and x varied with number of screw turns, equations were developed for K and x for each bubbler based on regression of flow data. Correlation between calculated flow rates with the equations and measured flow rates was in the range of 80% to 90%.

Field trials were conducted in Tucson, Arizona to evaluate the effects of certain aspects of water and crop management on germination and stand establishment of directly seeded guayule (Parthenium argentatum), using drip irrigation. In a study in May, 1983, seed cover and seed placement were the principle experimental variables, under three irrigation frequencies and two water levels. Vermiculite covered seed plots had significantly more germination than the non-covered plots. Germination was higher in seed rows placed at 4 cm from the drip line than at 9 cm. In a study in October, 1983, irrigation frequency, irrigation water level, and seed placement were analyzed for their effect on stands during germination and post-emergence phases of growth. Significant differences were found as a result of seed placement and it's interaction with irrigation water level. Highest stands occurred under the low water level treatment, with seeds placed at a distance of 5 cm from the drip line.

Fast growing, highly productive, low N demanding, C3 and C4 perennial rhizomatous grasses (PRGs) have the potential to be excellent future lignocellulosic bioenergy feedstocks under temperate climatic conditions. Biochar, a black carbon sequestering material, and an active plant growth promoting rhizobacteria (PGPR) community have both been shown to enhance plant growth, although they have not been tested with relevant PRGs under Québec (high-latitude temperate zone) field conditions. Agronomic field studies were conducted on bioenergy crop production with two grass species (switchgrass - SG - C4 species and reed canarygrass - RCG - C3 species) using biochar (0 or 20 t ha-1) and PGPR (able to mobilize soil phosphorus or supply nitrogen) as soil amendments. The SG research was conducted at three field sites in southern Québec. The sites represented three soil types in two climatic regions (sites 1 and 2 in southwestern Québec and associated with McGill University, and site 3 associated with Laval University in southeastern Québec). In these studies, interactions occurred between biochar and PGPR for many of the measured switchgrass growth variables (height, stand density, tiller DWs, dry biomass production, N export) that resulted in increasing growth and biomass yield at the comparatively warmer growing season sites 1 and 2. At site 3, with a cooler summer climate, both biochar and PGPR caused improved levels of at least some variables. The reed canarygrass work was conducted at one site, associated with McGill University, for 2 years. A positive biochar by N interaction (P < 0.05) occurred for both C4 and C3 grass productivity. Biochar amendment tended to increased nitrogen use efficiency (NUE) at 50 kg N ha-1 and 150 kg N ha-1 for C4 and C3 grasses, respectively. A similar pattern was observed for apparent N recovery for both PRGs and C content of reed canarygrass. Based on three years of data collection at three sites (nine site-years) for switchgrass, plus 2 additional site years for reed canarygrass, PGPR along with biochar generally, and particularly in the second and third years of the experiments promoted bioenergy plant growth and N use efficiencies, demonstrating their potential utility in development of low-input bioenergy feedstock production systems for high-latitude temperate zone areas, such as southern Québec. / Ayant de la croissance rapide, hautement productive et une faible consommation de N, les herbes vivaces à rhizomes (GPR) C3 et C4 ont le potentiel d'être d'excellentes futures matières premières bioénergétiques lignocellulosiques dans des zones climatiques tempérées. Le biochar, un matériel noir séquestrant de carbone, est une communauté actif de PGPR dont tous les deux ont été demonstrés à améliorer la croissance des plantes, cependant elles n'ont pas été testées avec des PRG pertinentes dans les conditions Québecoises (zones tempérées de haute latitude). Des études agronomiques ont été menées sur la production agricole des cultures pour bioénergie avec deux espèces modèles (panic érigé-C4, et alpiste roseau-C3) en utilisant le biochar (0 ou 20 t ha-1) et PGPR (mesure de mobiliser le phosphore du sol ou de l'azote) comme amendements du sol dans trois champs dans le sud du Québec. Les sites ont représenté les trois types de sol dans deux régions climatiques (sites 1 et 2 dans le sud-ouest du Québec et associé à l'Université McGill, et le troisième site associé à l'Université Laval dans le sud-est du Québec). Dans ces études, des interactions significatives ont eu lieu entre le biochar et PGPR pour la plupart des variables mesurées croissance (hauteur, densité, matière sèche de tiges, rendement de matière sèche, niveau de N) sur les sites avec une saison de croissance relativement chaude (1 et 2). Sur le site 3, avec un climat plus frais pendant l'été, le biochar et PGPR ont provoqué des niveaux améliorés d'au moins certaines des variables pendant les trois années. Une interaction entre le biochar et N (P <0.05) a été observée pour la productivité des herbes de C4 et C3. Le biochar à augmenté le NUE aux niveaux de 50 kg N ha-1 et 150 kg N ha-1 pour les herbes C4 et C3, respectivement. Une tendance similaire a été observée pour N pour les GPR et teneur en C d'alpiste Roseau RCG. D'après les données sur trois sites, et collectionnées pour trois années (neuf années-sites), le PGPR ainsi que le biochar améliore la croissance des plantes et l'utilisation efficace de N, ce qui démontre leur potentielle dans le développement des systèmes bioénergetiques à faibles intrants de production des matières premières dans des zones tempérées d'haute latitudes comme le sud du Québec.

Predicted future increases in atmospheric CO2 concentration and air temperature may significantly affect, timothy (Phleum pratense L.), a widely grown perennial forage grass across eastern Canada. A study was done to assess the impacts of predicted increases in CO2 concentration and temperature under contrasted N fertilization on timothy growth, photosynthetic rate, nutritive value, and root degradability as it relates to C sequestration potential. Response of timothy biomass, photosynthesis, and nonstructural carbohydrate and fibre concentrations to CO2 and temperature depended on soil N availability. Future timothy production will likely remain unchanged with potential increases in photosynthesis and the nonstructural carbohydrate concentration available for animal consumption. Future conditions may also reduce forage ruminant N supply without affecting either fibre concentration or digestibility. By decreasing root degradability, these conditions could improve the C sequestration potential of timothy. / Les changements prédits en termes de concentration en CO2 et de température pourraient affecter la croissance de la fléole (Phleum pratense L.), une espèce pérenne utilisée comme plante fourragère dans l'est du Canada. Une étude a été réalisée afin de mesurer l'impact de l'augmentation de concentration de CO2 et de la température, sous un régime contrasté de fertilisation azotée, sur la croissance, la photosynthèse, la valeur nutritive, et la capacité de séquestration du C en mesurant la dégradabilité des racines de la fléole des prés. Les réponses de la fléole au CO2 et à la température ont varié selon le niveau de fertilisation azotée. Sous les conditions climatiques futures, le rendement de la fléole serait peu modifié alors que la qualité nutritive pourrait augmenter en raison d'une concentration plus élevée en sucres solubles. Les futures conditions auront peu d'impact sur la concentration en fibres alors que l'azote de la plante pourrait diminuer. Les conditions futures pourraient améliorer la capacité de séquestration du C de la fléole en diminuant la dégradabilité racinaire.