Browsing by Subject "Nitrogen cycle"
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Item Effect of nitrogen on the uptake of perchlorate by plants(Texas Tech University, 2004-08) Joseph, Preethi CPrevious studies have shown that plants were tolerant to perchlorate and will accumulate perchlorate in plant tissues. The objectives of this research were to determine the effect of nitrogen type (Ammonium or Nitrate) and concentration on the rate and extent of perchlorate uptake in lettuce and soybean plants. Studies were conducted in plant growth chambers and in greenhouses using sand as a support medium. Treatments included studies with defined laboratory fertilizer solutions at varying concentrations of nitrogen and constant concentrations of other ions, as well as with commercial NH4+ and NO3- based fertilizers at varying loading rates. The growth of plants was affected in response to varying nitrogen concentrations and sources. The perchlorate accumulation in plants was determined on a weekly basis by extracting the plant and sand samples and analyzing them for perchlorate levels using ion chromatography. In all experiments, plant growth was severely affected, and in most cases, plants did not proceed past the two leaf stage of growth. Perchlorate was detected in all plants with peak concentrations occurring between 3-6 weeks of growth and declining thereafter. The plant perchlorate concentrations were higher in plants fertilized with ammonium fertilizer than with the nitrate fertilizer although the difference in plant growth between treatments makes it difficult to say whether this would be observed under normal conditions. The perchlorate concentration also generally increased with an increase in nitrogen concentrations applied to the plants. Overall, the effects of source and nitrogen concentration are unlikely to have significant effects on perchlorate uptake in plants under normal environmental conditions.Item Nitrogen and phosphorus utilization by beef cattle fed three dietary crude protein levels with three supplemental urea levels(Texas Tech University, 2003-05) McBride, Kevin WayneThree dietary CP levels (11.5, 13.0, and 14.5% of DM) and three supplemental urea levels (100, 50, and 0% of supplemental CP from urea) were used in a 3 x 3 factorial arrangement of treatments to determine performance, blood urea N (BUN), and N and P balance. Crossbred steers (n = 27; average BW = 315 kg) were blocked by BW and individually fed the dietary treatments in a completely randomized block design. A steam-flaked corn-based diet was fed, with upplemental CP supplied by either urea, a 50:50 blend (N basis) of urea and cottonseed meal (CSM), or CSM (100, 50, and 0% of supplemental CP from urea, respectively). Steers were used in three nutrient balance collection periods (NBCP) at the beginning, middle, and end, of the feeding period. Venous jugular blood was obtained at the start and end of each NBCP. No dietary CP level x supplemental CP source interactions (P > 0.10) were observed for any variables. Steer DMI, ADG, and gain efficiency did not differ (P > 0.10) among treatments. For each NBCP, urinary total N (g/d), urinary urea N (UUN), and BUN increased linearly (P < 0.10) as dietary CP level increased. For NBCP 1 and 3, fecal N output increased linearly (P < 0.10) as supplemental CP from CSM increased. For NBCP 2 and 3, UUN decreased linearly (P < 0.10) as supplemental urea level decreased. For NBCP 1, fecal and urinary P excretion (g/d) increased linearly (P < 0.10), and P retained (% of intake) decreased linearly (P < 0.10), as dietary CP level increased. Phosphoms intake increased linearly (P < 0.10) as supplemental CP supplied by CSM increased for each NBCP. Fecal P output increased linearly (P < 0.10) in all NBCP, and urinary P excretion in NBCP 1 and 2 increased linearly (P < O.IO) as supplemental urea level decreased. Phosphoms retained (% of intake) decreased linearly (P < 0.10) as supplemental CP from urea decreased for NBCP 3. Results suggest that as dietary CP level increased, N retention (% of intake) decreased, and as supplemental CP supplied by urea decreased, P balance decreased in feedlot steers. As days on feed increased, less (P < 0.10) N and P were retained, suggesting the potential to decrease N and P excretion by feeding less N and P as the feeding period progresses.Item Quantifying the role of agriculture and urbanization in the nitrogen cycle across Texas(2012-05) Meyer, Lisa Helper; Yang, Zong-liang; Dickinson, Robert E.; Breecker, Daniel O.Over-enrichment of nutrients in coastal waters has been a growing problem as population growth has enhanced agricultural and industrial processes. Enhanced nitrogen (N) fluxes from land to coast continue to be the result of over fertilization and pollution deposition. This over-enrichment of nutrients has led to eutrophication and hypoxic conditions in coastal environments. This study was conducted along the Gulf of Mexico, through the state of Texas, in order to quantify all agricultural and industrial sources of N in a region which contains a large precipitation gradient, three major metropolitan areas, and one of the top livestock industries in the United States. Nitrogen inputs from fertilizer, livestock, crop fixation, and oxidized deposition from both dry and wet atmospheric processes were quantified and compiled into a Texas Anthropogenic N Budget (TX-ANB). In addition, comparisons and regional enhancements were made to the Net Anthropogenic Nitrogen Input dataset (NANI toolbox), which is a national dataset developed at Cornell University by Hong et al. [2011]. These enhancements ultimately will help understand the full pathways of anthropogenic influences on coastal systems in a regional setting. All three datasets (NANI, NANI Regional, and TX-ANB) indicate agriculture to be the primary contributor to the N cycle in Texas, with TX-ANB showing 38% of inputs from fertilizer, 37% of inputs from livestock, and 2% of inputs from legumes. N input due to atmospheric deposition of oxidized N clearly highlights urban areas, indicating a strong influence of urbanization on the N cycle due to anthropogenic impacts; 23% of N input in Texas is the result of deposition of oxidized N. Quantification of inputs spatially indicates a strong enhancement of N from human influence in the coastal plain where nutrient export is heightened by major storm events. This enhancement of N along a coastal drainage area will likely have a negative impact on downstream environments.