Chung Siu-wah. / Thesis (M.Phil.)--Chinese University of Hong Kong. / Bibliography: leaves 40-46.

<p> Carinata (<i>Brassica carinata</i> A. Braun), a non-food oilseed crop and an alternative bio-jet fuel feedstock, has received attention for its potential as a low-input option for production in the semi-arid regions of the Northern Great Plains of USA. The crop has a lower N fertilizer requirement as compared to the other oilseeds, suggesting less negative impact on soils and GHGs emissions. Carinata is a new crop to South Dakota (SD), thus, the best management practices have yet to be developed. In addition, no sufficient research to address the impact of growing carinata on soils and GHG emissions has been reported. The objectives of the study were to: (i) evaluate the response of seed yield and agronomic traits for carinata to N and S fertilizer rates, and (ii) evaluate the impact of growing carinata with different rates of N and S fertilizers on select soil properties and GHG emissions. Field experiments were conducted in 2017 and 2018 to assess the response of carinata to four N rates (56, 84, 112 and 140 kg N ha^&ndash;1) and three S rates (0, 22 and 45 kg S ha^&ndash;1) and) at Brookings, SD under conventional tillage. Increasing N fertilizer rate significantly increased plant height, branching, lodging severity, number of pods plant^&ndash;1 but significantly decreased seed oil concentration. Increasing S fertilizer rate significantly increased plant height, branching, agronomic traits, seed yield, and seed oil concentration. This study showed that the economically optimal N rate was 85 kg N ha^&ndash;1 and the economically optimal S rate was 36 kg S ha^&ndash;1. Application of N fertilizer had minimal impact on soil parameters; N fertilizer increased soil EC, soil organic carbon (SOC), stable carbon, labile N, soil K, and soil P. Sulfur fertilizer decreased soil EC, SOC, labile N, and soil inorganic N content but increased extractable S content. Results from GHG emissions showed that, in addition to soil temperature and moisture conditions, N fertilizer increased CO₂&not; and N₂O emissions, whereas, S fertilizer application did not affect emissions. Methane fluxes fluctuated due to the impact of soil temperature and moisture. </p><p> Findings from this study suggested that carinata has low nutrient requirements compared to the traditional crops grown in SD, and optimum N and S requirements for this crop were developed. This study also suggested that, in general, carinata has minimal impacts on soils and GHG emissions, however, a long-term monitoring of soils and GHG fluxes under different rotations, soils and environmental conditions can be beneficial in understanding the impacts associated with carinata production.</p><p>

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A study was made to compare the protein and forage yield and root dry weight data of five pasture mixtures as influenced by two clipping frequencies (28 and 35 day clipping intervals), three irrigation intervals (1 inch every 5 days, 2 inches every 10 days and 4 inches every 20 days) and four levels of nitrogen fertilization (0, 50, 100, and 200 pounds per acre). The study was conducted at the Greenville Farm, Logan, Utah. The farm has about 1 percent surface slope and is a well-drained Millville silt loam that occurs on an alluvial fan. It is high in potash and phosphorous and is alkaline, having a pH of 7.9 to 8.2. Only mixtures gave significant percent forage protein results . Clipping, irrigation and fertilization treatments did not significantly affect the percent of forage protein but did affect the forage yield and thus the total protein production per acre. The total forage protein yield increases were n early lineal with the nitrogen treatment increases. The yield of forage from the 35 day clipping frequency was greater than from the 28 day clipping frequency for all five mixtures. The mixtures containing alfalfa showed greater response to the harvest frequency in increased forage yield than the other mixtures. All nitrogen applications gave forage yield increases. The first 50 pound increment gave the greatest and the second 50 pound increment gave the l east forage yield response. The different irrigation intervals, with the same total seasonal water applied, resulted in no significant forage yield differences. Ladino clover had the greatest root dry weight per acre with the 28 day harvests and 50 pounds of nitrogen. The alfalfa and grass root dry weights per acre were largest with the 35 day harvests, the first 50 pound increment of nitrogen application and the longest irrigation lnterval. A mixture of alfalfa and intermediate wheatgrass had the high alfalfa root dry weight and the low grass root dry weight yield per acre. Ladino clover roots were high in both the percent and pounds of total available carbohydrates (TAG) per acre with the 20 day irrigation interval and with five harvests. Grass roots percent and total pounds of TAG per acre were high with five harvests. Alfalfa root TAG per acre was nearly double with four harvests over five harvests and showed the greatest response to the first 50 pounds of nitrogen and the 20 day irrigation interval. Five harvests gave higher root to forage (R/F) ratios for all mixtures except the ladino clover-grass mixture. Zero pounds of nitrogen gave the highest R/F ratio for the grass-only mixture. Fifty pounds of nitrogen gave the highest R/F ratios for the other four mixtures.

Legumes contribute significantly to sustainable agriculture because of their high protein content. This intrinsic nitrogen is the product of a mutualistic association between their roots, and a group of soil bacteria, collectively known as rhizobia. The rhizobium-legume symbiosis is a complex developmental process that involves rhizobial entry and differentiation, coupled in space and time, with the development of a root organ (the nodule) and is subject to modulation by environmental factors. Salt stress is a strong negative regulator of rhizobium-legume symbiosis, but despite its agricultural impact, the mechanism of salt regulation of rhizobium-legume symbiosis is poorly understood. This dissertation addresses this issue with focus on early rhizobium-legume signaling and maturation of nodules, using the model legume Medicago truncatula. The rhizobium-legume symbiosis is initiated with a molecular dialogue between the symbiotic partners, followed by the entry of rhizobia inside the host. These processes are under tight genetic regulation and involve the symbiotic induction of several host genes. I used a candidate gene-approach to locate the temporal intersection of salt and rhizobium-legume signaling and found that the ionic component of salinity hyperinduces Early Nodulin 11 (ENOD11) and ERF Required for Nodulation 1 (ERN1). I also found that the hyperinduction of ENOD11 requires two symbiotic rhizobial signals- Nod factors (NF) and succinoglycan and the host transcription factor Nodulation Signaling Pathway 2 (NSP2). In order to explore the possibility of an extensive transcriptional re-programming during rhizobium-legume signaling in the presence of salinity, I profiled the host root transcriptome and discovered strong transcriptional upregulation by salt, of several host genes associated with NF perception, rhizobial infection and ubiquitination. Curiously, I found that the hyperinduction of these genes correlate with an inhibition of rhizobial entry into the host. These findings highlight that early rhizobium-legume signaling and rhizobial colonization of the host are under tight transcriptional regulation of the host. Despite the early inhibition of infection, few nodules develop under salt stress. However, these nodules are morphologically abnormal, indicating that salinity must interfere with nodule maturation, a prerequisite for nitrogen fixation. Consistent with the theme of early symbiotic signaling, I found host genes involved during the early stages of nodule differentiation to remain highly expressed in nodules that developed under salt stress, suggesting a delay in maturation. This inference was further corroborated when I found that genes associated with the later stages of nodule development and nitrogen fixation showed decreased expression in the presence of salt. Additionally, I observed that this developmental shift of nodules under salinity was associated with differential accumulation of osmolytes, such as, proline betaine and homostachydrine in the salt-stressed nodules. Together, my work provides a mechanistic understanding of the intersection between nodulation and salt signaling, a question of major agricultural impact.

The following herbicides were evaluated for their effect on perennial grasses and water pollution in El Salvador, Central America: MSMA (monosodium methanearsonate), DSMA (disodium methanearsonate), cacodylic acid (hydroxydimethylarsine oxide), paraquat (1 ,1 'dimethyl- 4,4'-bipyridinium ion), dalapon (2,2-dichloropropionic acid), amitrole (3-amino-s-triazole), atrazine (2-chloro-4-(ethylamino)-6-(isopropylamino)- s-triazine), diuron (3-(3,4-dichlorophenyl)-1,1-dimethylurea), and karbutilate (m-(3,3-dimethylureido)phenyl-t-butylcarbamate), The herbicides were sprayed on drainage channels at different dosage levels, Some plots received one application, others received two, and still others received three applications. All herbicides except atrazine effectively controlled perennial grasses, Cacodylic acid was the most effective contact chemical, with dosage levels of 7 and 10 kg/ha achieving 77 percent control of the grasses after two applications, Four and 6 kg/ha of amitrole produced 67 percent during the same period, but control of amitrole then increased while control of cacodylic acid decreased. After three applications, 5 kg/ha of MSMA yielded 88 percent control, MSMA was more effective than DSMA or dalapon, No significant increase in control was obtained by alternating dalapon and organic arsenicals. A single application of 12 kg/ha of diuron and karbutilate effectively controlled perennial grasses for 6 weeks. During the dry season, a single application of MSMA at 5 kg/ha, cacodylic acid at 10 kg/ha, and paraquat at 2 kg/ha each yielded over 70 percent control after 8 days. Water samples were taken during rainstorms that occurred shortly after application of diuron, MSMA, and cacodylic acid, The highest concentration of diuron was 1,8 ppm, Samples containing MSMA and cacodylic acid were analyzed for arsenic, and in no case was the concentration greater than .5 ppm, These low concentrations likely would not be hazardous to crops, animals, or fish.

The purpose of this thesis is to describe dyers woad and to establish v means for control of the weed in northern Utah. Logan was chosen for studying germination of the weed, and interaction of dyers woad and alfalfa stands. Collinston was selected for screening trials of herbicides for the control of dyers woad. The thesis contains information on the phenology of dyers woad and suggestions for control of the weed.

Salt-affected soils make up much of the bottom-lands of the arid and semiarid areas of the western United States and are especially prevalent in irrigated regions. Such soils require special remedial measures, management practices, and salt tolerant crops if they are to have economic value.