Atriplex canescens (Pursh) Nutt., Atriplex polycarpa (Torr.) Wats., and Atriplex lentiformis (Torr). Wats. have been considered candidate perennial shrubs for revegetation of abandoned farmlands in southern Arizona. Objectives of the 1992-1994 field studies were to investigate the establishment characteristics of populations of these species and to estimate water requirements for establishing transplants and/or seedlings under a line-source sprinkler irrigation system. During the summer on a sandy loam soil, seedling establishment occurred at total water amounts greater than 200 mm but was absent at amounts less than 150 mm The poor stand establishment was attributed to high soil temperatures at 1 to 3-cm depth which were not optimum for seed germination. Transplant survival percentages were greater than 89% except for accessions of A. canescens var. linearis (S. Wats.) Munz, which were affected by rabbit herbivory. Transplants were successfully established by planting into a wet soil profile followed by cumulative precipitation amounts of 60 to 70-mm. Establishing Atriplex taxa during the summer using transplants was more promising than direct-seeding. On a silt loam soil during the 1993 winter, stand establishment was not increased under cumulative precipitation and irrigation amounts greater than 100 mm compared to 66 mm of precipitation. On a clay loam soil during the 1994 winter, supplemental irrigations increased the probability of seedling emergence and stand establishment was higher under total water amounts greater than 100 mm. Differences between years in response to the line-source irrigation gradient were attributed to the number of consecutive days when soil moisture at 1 to 3-m depth was high for optimal seedling emergence. During the winter, plant heights were not affected by total water amounts between 182 to 248-mm (1993) and between 119 to 150-mm (1994), whereas heights were reduced at total water amounts less than 100 nun in 1993, and less than 90 mm for all species in 1994 except A. polycarpa. In southern Arizona where precipitation is erratic in amount and timing, supplemental irrigations may increase the probability of successful seedling establishment of Atriplex shrubs.

A High N fertilizers citrus rates may contribute to a rise in the appearance of groundwater NO₃ around groves in central Arizona. Nitrogen fertilizer recommendations need to be reevaluated for citrus due to recent changes in fertilizers, irrigation technology, and increasing groundwater NO₃. Studies were initiated to optimize fertilizer N management for microsprinkler-irrigated citrus. Navel oranges were planted in Jan. 1997 with varying N rates and frequency of liquid urea NH₄-NO₃ or granular controlled-release fertilizers (CRFs) in order to determine tree response, N partitioning, N balance, and residual soil N. Trees grew slowly in 1997 with no more than 6% of the fertilizer N taken up by trees, while < 94% of fertilizer N remained in the top 0.9 m of soil. Leaf N was higher in fertilized plots than in controls as trees grew rapidly in 1998 with < 25% of the fertilizer N taken up by the trees. The soil contained low NO₃ concentrations, suggesting most of the fertilizer N was leached. Nitrogen is not needed during the first season after planting and rates of 68 to 136 g N tree⁻¹ applied in monthly intervals during the second season maintain adequate tree growth and N reserves. Application of CRFs resulted in little tree response during the two year study. Soil inorganic N was highest in the surface 0.6 m in 1997. In 1998, ammonium sulfate treatments resulted in higher NO₃ leaching than plots that received CRFs. Eight-year old 'Redblush' grapefruit trees were treated with two N rates and three fertigation frequencies in a factorial arrangement. There no differences in trunk diameter, or fruit quality on trees between 1996 and 1998. Leaf N content was > 18 mg kg⁻¹ in all plots in 1996. Leaf N declined in Aug. 1997 and control plots had lower leaf N than the other treatments. Yields tended to be the greatest at high N rates with monthly fertigation. Soil N levels were proportional to fertilizer N inputs. In 1998, the high N treatment at weekly and monthly frequencies increased leaf N compared to the other treatments. Results suggest that N rates of 272 to 408 g tree⁻¹ year⁻¹ at weekly or monthly frequencies may be optimal for desert-grown mature grapefruit.

In jojoba, flower buds are typically produced at every other node on new growth near branch tips. An increase in the number of branch tips (branching frequency) could possibly increase flower bud and fruit production. Studies were conducted to determine the effects of three concentrations of Benzyladenine (BA), Gibberellin4+7 (GA), and Promalin (a mixture of BA and GA) on branching and flower production of three jojoba clones. Treatments involving pinching and untreated control plants were also included. The growth regulators had a significant effect on both branching and flower bud production, and clones differed in their response. For the most responsive clone, the most effective treatments (100 ppm GA and 100 ppm Promalin) resulted in 133% and 110% increase in flower buds after 17 months, respectively. The increase in flower buds was associated with an increase in the number of growing tips and node production. Similar responses were observed in both greenhouse and field experiments. The results of these studies indicate that growth regulators can be used to significantly increase flower bud production on jojoba.

<p> Most breeding programs aim at developing superior germplasm and better cultivars that combine high yield, disease and pest resistance, and end-use quality to satisfy the requirements of the growers as well as industry. A population, consisting of 138 F_2-8 recombinant inbred lines (RILs) derived from a cross between 'Steele-ND' and ND 735, was evaluated to study the inheritance pattern of the septoria tritici blotch (STB)-resistant genes, agronomic and quality traits. The genetic map of this population was generated using Diversity Arrays Technology (DArT) (Triticarte Pty. Ltd., Canberra, Australia), a high-throughput genome analysis method. The framework map made of 392 markers, including 28 simple sequence repeat (SSR) markers and 364 DArT markers, spanned a total distance of 1789.3 cM and consisted of 17 linkage groups. The map position of quantitative trait loci (QTL) found in this study coincided with the map position of durable STB resistance genes, Stb1. Thirteen QTL were detected for agronomic and quality traits. More saturation of the current map is needed to explore more QTL for this population.</p>

<p> Nitrogen (N) fertility and irrigation costs are the greatest input expenses required for rice production in Mississippi, therefore N management and irrigation should be conducted in efficiently. Field experiments were conducted at the Delta Research and Extension Center in Stoneville, MS, and the LSU AgCenter in Crowley, LA, to evaluate water and nitrogen management practices. Nitrogen use efficiency and yield were not different for alternate wetting and drying (AWD) systems compared to a traditional continuous flood. Additionally, experiments were conducted to test for differences comparing two experimental designs, randomized complete block (RCB) and split-plot (SP), for N-rate response trials in Mississippi. Rice grain yield response to N-rate was similar for RCB and SP designs, therefore either experimental design would be appropriate for N-response experiments in rice. Increasing efficiency of water and N management practices further improves environmental and economic benefits from rice production in Mississippi.</p>

<p> The study of agriculture practiced by the Mixtec people, or &ldquo;the people of the rain&rdquo; (<i>&Ntilde;uu savi</i>), in the highlands of southern Mexico reveals successful adaptation strategies for growing rainfed crops in an unpredictable and ever changing climate. Both culture and environment have been shaped by a long and challenging history, which continues to bear relevance in this era of globalization and climate change. </p><p> My research from 2009 &ndash; 2011 focused on farmer strategies for dealing with climatic variability in the Mixteca Alta Region of Oaxaca, Mexico. It was the product of a close collaboration with the farmer-to-farmer training network, the Center for Integrated Small Farmer Development of the Mixteca Alta (<i>Centro de Desarrollo Integral Campesino de la Mixteca Alta</i>, CEDICAM). </p><p> My dissertation is organized in four chapters. Chapter 1 contextualizes my research by examining farming traditions of the Mixteca Alta that originated in different historical moments. I also provide a summary of the political economy of labor and sustainable farming. </p><p> Chapter 2 examines the social, environmental, and cultural conditions of farming in the Mixteca Alta. Based on in-depth interviews with farmers from two communities, I trace how changes in farming systems has reflected both traditions of farming and an increasingly globalized economy. </p><p> I found that a combination of agroecological strategies were important for families to approach self-sufficiency in grain production under highly variable rainfall conditions. Important changes in cropping systems were occurring, particularly shifts towards more precocious crop varieties. It appears that changes in cropping systems have been the result of social disintegration, soil degradation, and climatic changes. </p><p> Chapter 3 describes participatory research with farmers in the CEDICAM network, as well as climatic studies, that aimed to place climate change mitigation and adaptation into the hands of small farmers. I facilitated workshops in which groups of small farmers described how they had adapted to and prepared for past climate challenges. Farmers reported that their cropping systems were changing for multiple reasons: more drought, later rainfall onset, decreased rural labor, and labor-saving technologies. Examination of climate data found that farmers&rsquo; climate narratives were largely consistent with formal climatology data products. There have been increases in temperature and rainfall intensity, and an increase in rainfall seasonality that is likely perceived by farmers as later rainfall onset. </p><p> I conclude with Chapter 4, which highlights CEDICAM&rsquo;s contribution to mobilizing farmers in the Mixteca Alta region. They are taking action to reforest territories and advance agroecological farming. This chapter also reflects on how collaborative research outcomes contributed to CEDICAM&rsquo;s future outlook on farmer led research. CEDICAM was particularly interested in improving soil cover management and crop selection. CEDICAM as a network continues to promote the social conditions for agroecology to flourish. (Abstract shortened by UMI.)</p>

Thesis (Ph.D.)--North Dakota State University, 2006. / (UnM)AAI3213959. Adviser: W. A. Berzonsky. Source: Dissertation Abstracts International, Volume: 67-04, Section: B, page: 1753.

Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2007. / Source: Dissertation Abstracts International, Volume: 68-11, Section: B, page: 7031. Adviser: Frederick E. Below. Includes bibliographical references. Available on microfilm from Pro Quest Information and Learning.

Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2008. / Source: Dissertation Abstracts International, Volume: 69-05, Section: B, page: 2678. Adviser: Emerson D. Nafziger. Includes bibliographical references. Available on microfilm from Pro Quest Information and Learning.

Thesis (Ph.D.)--University of Illinois at Urbana-Champaign, 2009. / Source: Dissertation Abstracts International, Volume: 70-06, Section: B, page: 3245. Adviser: Michelle Wander. Includes bibliographical references. Available on microfilm from Pro Quest Information and Learning.