Winter cover crops grown in rotation with grain crops can be an efficient integrated pest management tool (IPM). However, cover crop biomass production and thus successful provisioning of ecosystem services depend on a timely planting and cover crop establishment after harvest of a cash crop in the fall. One potential management adaptation is the use of short-season soybeans to advance cover crop planting date in the fall. Cover crops planted earlier in the fall may provide a greater percentage of ground cover early in the season because of higher biomass accumulation that may improve weed suppression. However, adapting to short-season soybeans could have a yield penalty compared to full-season soybeans. In addition, it is unclear if further increasing cover crop growing season and biomass production under environmental conditions in Kentucky could limit nitrogen and water availability for the next cash crop. This thesis combines the use of field trials and a crop simulation model to address the research questions posed. In Chapter 1, field trials evaluating yield and harvest date of soybean maturity group (MG) cultivars from 0 to 4 in 13 site-years across KY, NE, and OH, were used to calibrate and evaluate the DSSAT crop modeling software (v 4.7). The subsequent modeling analysis showed that planting shorter soybean maturity groups (MG) would advance date of harvest maturity (R8) by 6.6 to 11 days per unit decrease in MG for May planting or by 1 to 7.3 days for July planting. The earliest MG cultivar that maximized yield ranged from MG 0 to 3 depending on the location, allowing a winter-killed cover crop to accumulate between 257 to 270 growing degree days (GDD) before the first freeze occurrence when soybean was planted in May, and between 280 to 296 GDD when soybean was planted in July. Winter-hardy cover crops could accumulate 701 to 802 GDD following soybean planted in May and 329 to 416 GDD after soybean planted in July. In Chapter 2, a two-year field trial was conducted at Lexington, KY to evaluate the effect of a soybean – cover crop rotation with soybean cultivars MG 1, 2, 3 or 4 on cover crop biomass and canopy cover, and on weed biomass in the fall and the following spring. Results showed that having cover crops was an efficient management strategy to reduce weed biomass in the fall and spring compared to no cover treatment. Planting cover crops earlier in the fall after a short-season soybean increased cover crop biomass production and percentage of ground cover in the fall, but not the following spring. Planting cover crop earlier after a short-season soybean did not improve weed suppression in the fall or spring compared to a fallow control with full-season soybean. Having a fall herbicide application improved weed control when there was a high pressure of winter annual weeds. By the spring, delaying cover crop termination increased cover crop biomass but also did weed biomass. In Chapter 3, a soybean – cover crop – corn rotation was simulated to evaluate the effect of different soybean MG and cover crop termination, as well as year to year variability on water and nitrogen availability for the next corn crop in Lexington, KY. Simulations showed that when cover crops were terminated early, they did not reduced soil available water at corn planting. However, introducing a non-legume cover crop reduced total inorganic nitrogen content in the soil profile by 21 to 34 kg ha-1 implying 15 to 30 kg ha-1 less in corn nitrogen uptake. Cover crop management that was able to maintain similar available water values than fallow treatment while minimizing nitrogen uptake differences was cover crops planted after soybean MG 4 with an early termination. However, the best management strategies that will maximize ecosystem services from cover crops as well as cash crop productivity may need to be tailored to each environment, soil type, irrigation management, and must consider year-to-year variability.

Since 2011, California has been under drought conditions. These conditions have not only affected water availability for farmers, but also production. California’s second most valuable crop, almonds, has been affected by drought conditions. This study used three models (Model 1-3) to describe almond yield variability from year to year and almond yield variability within a year in Kern County, CA. The study evaluated 185 almond farms that were classified in three locations (east side, west side and north west side). The years of the study were 2011 (wet year) and 2013-2015 (drought condition years). Model 1 determined a functional regression between almond yield and annual evapotranspiration during the 4 years of the study. The R2was 7.9%, meaning low association between both variables and high unexplained variability (92.1%). Model 2 evaluated year to year variation. A regression function between almond yield and annual evapotranspiration after adjusting for location, precipitation, chilling hours and year was made. The R2of this model 62.6%, and all the variables used had a p2was higher than Model 1; however, there was high unexplained variability (47.4%). Model 3 evaluated within-year variation. A regression function between almond yield and annual evapotranspiration after adjusting for tree age and location (east, west and northwest side) was made for each year (2011 and 2013 -2015). Coefficient of variation of evapotranspiration and soil available water storage were analyzed as additional variables in Model 3; however, they were not introduced in Model 3 due to the low increase in R2 in each year (2 of Model 3 for each year were, 60.4%, 49.7%, 53.8% and 53.2% for the years 2011, 2013-2015, respectively. Model 3 also had high unexplained almond yield variability in each year (39.6%-50.3%). This high unexplained variability leads to introduce additional variables to the functional regression model for further studies. Identifying these additional variables and having a functional regression model with high R2 would lead to understand howlow evapotranspiration could potentially lead to a positive response on yield in drought conditions; thus, making farmers improve water use efficiency and hence, lowering production cost. However, the high unexplained variability clearly indicates that evapotranspiration is only one of many factors that influence yield. If improved yield is an important outcome, future studies must examine large- scale almond-producing farms with multiple agricultural system variables.

Despite 25 years of concerted efforts by African governments to adopt consistent policies for increasing food production, hunger and poverty are still prevalent in the continent. Using Bernanke's conceptualization of the credit channel theory of monetary policy, the purpose of this correlational study was to investigate whether a subsidy program, the National Accelerated Agricultural Inputs Access Program (NAAIAP), affected the rates of fertilizer usage and food production in Kakamega County, Western Kenya. Purposive stratified sampling was used to select 114 participants consisting of 72 farmers in each of the 2 groups: NAAIAP beneficiaries and nonbeneficiaries. Participants completed a survey on fertilizer usage rates, income earned, and surplus maize yield. Data were analyzed using multiple regression to test whether there was a difference between the beneficiary and nonbeneficiary groups regarding income, surplus product, and the dependent variable of fertilizer usage. Results indicated that beneficiaries of NAAIAP credit program bought and prepared to use fertilizers significantly earlier than did their counterparts. Further, the results of multiple regression indicated significant positive correlation (p <.05) between income earned from sale of surplus maize yield and quantity of fertilizer used by farmers in Kakamega County. These findings suggest that NAAIAP improved food security and farmers' income in Kakamega Count. This study contributes to social change by recommending to subsidy program administrators in Kakamega County to consider policy changes. Such policy changes may improve program outreach to resource-poor farmers and improve income and product yield in the agricultural sector of Kenya.

The modern global agrifood system has had significant negative impacts on consumers and producers. This has precipitated the rise of local food systems that are purported to improve the health and livelihoods of consumers and producers. High expectations have led to significant public and private resources dedicated to the development of local food systems. Despite this, there has been little systematic research exploring the social and institutional conditions that facilitate or frustrate local food system development. Using a comparative case study approach, this study explored the ways local structural conditions, collective action, food system policies, and the political context affect the development of local food systems. Findings suggested truly robust local food system development requires either collective action or public policies and are more likely to exist and be successful depending on the political climate and the balance of power between land use interests in the community.

Plants reduce inorganic carbon to synthesize biomass that is comprised of mostly polysaccharides and lignin. Growth is intricately regulated by external cues such as light, temperature, and water availability and internal cues including those generated by the circadian clock. While many aspects of polymer biosynthesis are known, their regulation and distribution within the stem are poorly understood. Plant biomass is perhaps the most abundant organic substance on Earth and can be used as feedstock for energy production. Various grass species are under development as energy crops yet several of their attributes make them challenging research subjects. Brachypodium distachyon has emerged as a grass model for food and energy crop research. I studied rhythmic growth, a phenomenon important to understanding how plant biomass accumulates through time, and vascular system development, which has biofuel feedstock conversion efficiency and yield. Growth rate changes within the course of a day in a sinusoidal fashion with a period of approximately 24 hours, a phenomenon known as rhythmic growth. Light and temperature cycles, and the circadian clock determine growth rate and the timing of rate changes. I examined the influences of these factors on growth patterns in B. distachyon using time-lapse photography. Temperature and, to a lesser extent, light influenced growth rate while the circadian clock had no noticeable effect. The vascular system transports important materials throughout the plant and consists of phloem, which conducts photosynthates, and xylem, which conducts water and nutrients. The cell walls of xylem elements and ground tissue sclerenchyma fibers are comprised of cellulose, hemicelluloses, and lignin. These components are important to alternative energy research since cellulose and hemicellulose can be converted to liquid fuel, but lignin is a significant inhibitor of this process. I investigated vascular development of B. distachyon by applying various histological stains to stems from three key developmental. My results described in detail internal stem anatomy and demonstrated that lignification continues after crystalline cellulose deposition ceases. A better understanding of growth cues and various anatomical and cell wall construction features of B. distachyon will further our understanding of plant biomass accumulation processes.

Developing quantified establishment period estimates for newly planted trees will help set realistic goals for plant performance in the urban landscape. Nine years of tree planting records obtained from the city of Boston, MA and the town of Brookline, MA were used to derive samples of trunk caliper for hedge maple (Acer campestre), London planetree (Platanus x acerifolia), and red oak (Quercus rubra). Several site characteristics were measured to identify effects on newly planted tree growth. Breakpoint estimates of the piecewise regression models fell at 4 years and 6 years for London planetree and hedge maple respectively, showing establishment periods for urban trees are longer than the conventional 3 years. Pit area has a significant effect on caliper growth for London planetree and red oak, with larger growing spaces yielding larger trees. Observed soil bulk densities did not have a significant effect on caliper measurement for any of the species tested. Mean soil bulk density was 1.4 g/cm3, 1.45 g/cm3, and 1.49 g/cm3 for hedge maple, London planetree, and red oak respectively. Soil texture was significant for hedge maple only, with percent clay showing significant positive effects and percent sand as marginally significant. Pit type showed a significant effect on caliper measurement of London planetree with grass strips producing the largest caliper trees followed by open pits. Planting locations with tree grates produced the smallest caliper trees. Presence of perforated air vents produced significantly larger caliper trees than sites with an air vent present for red oak.

Weed control is an integral part of a successful overall production strategy in row- cropping systems and has the potential to reduce or eliminate yield losses that negatively affect profitability. Timely and correctly selected herbicide applications are the major keys for effective weed control in a majority of instances. However, there are negative factors that contribute to ineffectiveness and weed escape issues that currently lack viable options for management. Sparsely populated late-season weeds that emerge after lay-by herbicide applications and weeds that have become tolerant and resistant to traditional herbicide chemistries are of greatest concern. Historically, these weeds would have been pulled or chopped by hand or removed by cultivation, but with current production strategies built around conservation tillage and herbicide management practices, blanket disturbance of the soil through plowing is not a viable option. There is an immediate need for site-specific weed management to address these weed escapes while minimizing soil disturbance that reduces residual herbicide efficacy and lessens moisture losses that negatively effects the growing crop

In Bolivia we have three very valuable Andean grains: amaranth (Amaranthus caudatus), quinoa (Chenopodium quinua), and canihua (Chenopodium pallidicaule), which combined with cereals and legumes can become a complete and balanced food in order to combat the malnutrition that is so widespread in our region. In this study, various nutritional mixes were formulated, based on amaranth and other Andean crops, and the three best were chosen according to nutrition, palatability, and cost. They were: Andean Baby Food, Mixicereal, and Amaranth Cookie, which have an amino acid complement between 79% and 100% and give satisfactory amounts of protein, energy, and minerals for school-aged children. Afterward, the biological quality of the three foods was determined through biological evaluation studies, determining weight gain to be between 64.26 and 87.28, digestibility between 60% and 78%, and PER between 1.75 and 2.36. The cost of the three final products was less than 0.08 cents of an American dollar for every 100 grams of mix. Finally, sensory analyses were performed on the three products with 90 children, from 5 to 9 years old, from two rural schools in Quillacollo province, Cochabamba, and a preference for Mixicereal was observed. Based on these results, we conclude that the three mixes studied are excellent nutritional complements, with high biological value, sensory acceptability, and within the means of a population with scarce economic resources.

Verticillium wilt is a widespread soilborne disease of strawberry historically controlled by soil fumigation with methyl bromide (MB). MB was banned by the United Nations in 1995 and will be completely phased out by 2015. Research has concentrated on alternative methods of disease control without finding a single alternative able to replace MB in widespread disease control and yield increase. For the current study, strawberries were greenhouse grown in container pots filled with soil from both infested and non-infested areas of a commercial strawberry field in Watsonville, CA. Treatments included pre-plant soil fumigation with commercially available formulations of methyl bromide, chloropicrin, and 1, 3-Dichloropropene. Additional treatments included ozone gas (six treatments) and biological control (three treatments). Collected data included total plant yield, individual berry weight, number of fruit produced per plant, plant vegetative weight, infection status, and mineral concentration of fruit (calcium, magnesium, potassium, iron, zinc, manganese, carbon, and nitrogen). Plants grown in ‘clean’ soil were less likely than plants grown in ‘infested’ soil to be infected with Verticillium. Plants grown in soil treated with MB had higher plant weight and yield than did non-treated control. Ozone and biological control treatments did not have statistically higher yield than non-treated control plants nor statistically lower yield than plants grown in soil treated with MB. Individual berry weights had a narrow range while the number of berries produced per treatment had a wide range. Data suggests strawberry yield is dependent on the number of berries produced per plant. Plants with high vegetative weight produced the highest yield suggesting large plants produce many berries resulting in higher yield.

In the Central Coast of California, USA, wine grape growers are making efforts to identify weed control practices that promote biodiversity in their vineyards while maintaining yields. A field study was conducted in Paso Robles, CA in 2006 and 2007 evaluating the effect on Zinfandel grape-vine growth and production, groundcover plant, and ground dwelling arthropod communities of five weed control practices: 1) flumioxazin, 2) simazine, 3) cultivation, 4) cover crop, and 5) untreated control. The herbicide treatments had the lowest weed biomass followed by the cultivation, being approximately 10 and 2 times lower than the weed biomass of either the cover crop or untreated control treatments respectively. However, the differences in grape yield were not as evident. In 2006, a rainy year, the herbicides and cultivation treatments did not differ in grape yield, but the cover crop and untreated control had a reduction of approximately 20% compared with the other treatments. In 2007, a dry year, in comparison to the herbicide treatments, the grape yield reductions of cultivation were around 22%, and of the cover crop and untreated control around 48%. Although the cover crop reduced grape yield, it suppressed weed species considered important such as horseweed, panicle willowherb, scarlet pimpernel, and sowthistle. The cover crop, cultivation and untreated control had 4 to 50 times higher plant density and more than 15 times higher plant diversity compared to the herbicide treatments. The arthropod abundance differed among treatments only in 2007 being higher in the cover crop and untreated control. Also, there was a positive relationship between plant and arthropod diversity (r2 = 0.42, P = 0.02 in 2006; r2 = 0.64, P < 0.001 in 2007). Laboratory seed predation tests of the two most frequently captured carabid beetles, Calathus ruficollis and Tanystoma maculicolle, indicated their preferences for Brassica nigra and Capsella bursa-pastoris, which are considered common weed species in the region. Under field conditions, treatments with higher plant diversity and biomass favoured arthropod seed predation of these weeds, which was 20-40% in the cover crop and untreated control, doubling the predation observed in the herbicide treatments. The cultivation treatment balanced the benefits of promoting diversity while minimizing yield reductions due to weed competition. Our data indicated that the critical period of weed competition for Zinfandel grape vines occurred during budbreak-bloom period. Also, it was concluded that vines can tolerate a certain amount of weed competition, and that properly timing one pass post-emergence control tactics (e.g. cultivation or POST herbicides) could provide the necessary level of control to obtain the desired yields. However, under limited soil moisture conditions, the use of PRE herbicides could prove important to maintain vine yield and vigor. The results also illustrate how weed management practices that promote higher plant diversity and density have the potential to yield ecological services within vineyards by favoring the diversity and activity of other organisms.