For its fragrance, showy display and multi-colors, tall bearded (TB) iris (Iris germanica L.) has great potential as a specialty cut flower. This study was conducted to investigate the optimum nutrient management, especially nitrogen (N), of reblooming TB iris 'Immortality'. The objectives were to investigate the effects of N rate and form and phosphorus (P) rate on growth, flowering, and nutrient uptake, and to assess seasonal changes in the composition of nitrogenous compounds and carbohydrates. In general, greater N rates increased plant height, leaf SPAD reading, the number of inflorescence stems, plant dry weight, plant N content, and uptake of other nutrients. Spring flowering was more dependent on N stored from the previous year. Second bloom was largely influenced by N rate in the year of flowering. In spring, N uptake efficiency quadratically related with increasing N rate and was highest in the 10 mM N treatment. Percentage of tissue N derived from spring fertilizer decreased with increasing N rate applied from previous year. In comparison with N rates, P rates did not affect most of growth and flowering performances, but had slight influences on concentration of few nutrients (such as P, potassium, and boron). Considering N:P ratios in plant tissues in this study were low, these results imply 5 mM P rate, the lowest P rate tested in this study, was sufficient for growth and development of reblooming TB iris. NH4:NO3 ratios did not affect plant height, flowering, dry weight, and N uptake, suggesting TB iris may not have preference for either ammonium or nitrate N. Higher NH4:NO3 ratios increased leachate pH, which might influence uptake of iron, manganese, and zinc. Nitrogen and carbon were predominately allocated to rhizomes in December and to leaves in May, suggesting a process of nutrient storage and remobilization happened in TB iris with seasonal changes. Concentration of starch, sucrose, glucose, and fructose showed seasonal changes, while concentration of free amino acids did not. Starch was the major form of storage carbohydrates in December. Glutamate, alanine, aspartate, serine, and tyrosine were main constituents among free amino acids.

Research was conducted to compare the effects of composted dairy manure and raw dairy manure alone, or in combination with supplemental inorganic fertilizer, on soil chemical properties and Coastal bermudagrass [Cynodon dactylon (L.) Pers.] yield and nutritive value. Composted dairy manure was surface applied at rates of 14 (125 kg N ha-1), 29 (250 kg N ha-1) and 57 (500 kg N ha-1) Mg dry matter (DM) ha-1, and raw dairy manure was surface applied at a rate of 54 (420 kg N ha-1) Mg DM ha-1 to established bermudagrass. Selected compost and manure plots received supplemental inorganic N at rates of 56, 84 and 112 kg ha-1 cutting-1 or 112 kg ha-1 cutting-1 of supplemental N with supplemental inorganic phosphorus or potassium at rates of 112 kg P2O5 ha-1 yr-1 and 112 kg K2O ha-1 cutting-1, respectively. Composted dairy manure (29 and 57 Mg DM ha-1) or raw manure alone increased cumulative forage yields compared to the untreated check in both years of the study, but were less than those obtained using only inorganic fertilizer. Application of 56 kg N ha-1 cutting-1 or more of supplemental N to compost (29 and 57 Mg DM ha-1) or iv manure produced forage yields that were equal to or greater than those obtained using inorganic fertilizer alone. However, increasing compost rate did not increase tissue N concentrations regardless of supplemental inorganic N rate. Yield and tissue K concentrations were increased in the second growing season when supplemental inorganic K was applied to 29 Mg ha-1 of compost or 54 Mg ha-1 of raw dairy manure. No yield response was observed when supplemental inorganic P was applied to compost or manure. Soil pH and concentrations of NH4, NO3, K, Ca, Mg and Mn were increased by application of compost or manure. Soil P concentrations in the 0 to 5-cm zone exceeded 200 mg kg-1 when compost was applied at the high rate. Dairy manure compost was an effective nutrient source for bermudagrass hay production, but will require the use of supplemental N and, in some cases, K to achieve yields comparable to inorganic fertilizer.

The purpose of this study is to estimate the effect of Ontario’s Nutrient Management Act (NMA) on farm level profitability of dairy sector. NMA came into force in 2003 and sets standards for the storage and handling of nutrients for regulating farms that fit certain criteria to reduce the risk of nutrients entering surface water or groundwater, especially for farms with herd size that can produce Nutrient Units above a certain level (i.e. 300 Nutrient Units). While the Act may affect its regulated farms by incorporating additional compliance costs, it may not have the same effect on unregulated farms. Increase in the weighted-average production costs of all farms may lead to elevated milk price within a national cost of production (COP) pricing formula for dairy industry. A theoretical framework that describes the pathway by which farms’ economic performance can be affected by NMA is developed in this study. To empirically test whether NMA has effect on farm level profitability, a RE model is estimated by using the unbalanced panel data from Ontario Dairy Farm Accounting Project (ODFAP) from year 2000 to 2010. The empirical results of this study indicate that NMA may not have statistically significant effect on the profitability of regulated farms with no less than 300 Nutrient Units (NUs). A discussion is further developed to take into consideration factors that may affect this empirical results. / OMAFRA funding code: 200222

In the state of Virginia, population growth and the associated increases in municipal wastewater, along with the threat of EPA regulations, will increase the need for reductions in phosphorous (P) loads in surface waters in order to meet and maintain water quality standards for the Chesapeake Bay. Agriculture contributes 49% of P entering the Bay; therefore, it can be expected that agriculture will be targeted as a source of P reductions. Spatially variable physical and socioeconomic characteristics of a watershed and its occupant farms affect both the decisions made by farmers and the transport of nutrients. Evidence suggests that spatially variable characteristics should be considered when designing policies to control nonpoint sources of water pollution. However, spatial information can be expensive to collect and the evidence is not conclusive as to the level of information required to analyze specific pollution-control policies. The objective of this study was to estimate the accuracy of predicted compliance costs and changes in P deliveries resulting from mandatory buffer installation and mandatory nutrient management for three alternative levels of information, relative to the population of farms in a Virginia watershed. For each information case, an economic model, FARMPLAN, was used to determine the profit maximizing levels of inputs, outputs and gross margins. Selected crop rotations and P applications were used as inputs to the physical model, PDM, which estimated the levels of P delivered to the watershed outlet. The compliance cost and P reduction estimates for the three alternative cases were compared to those of the population to determine their accuracy. The inclusion of greater levels of spatial information will lead to more accurate estimates of compliance costs and pollution reductions. Estimates of livestock capacity are more important to making accurate predictions than are farm boundaries. Differences in estimates made using different levels of information will be greater when the farmers have greater flexibility in meeting the policy requirements. The implications are that additional spatial information does not aid in the selection of one policy over the other, but can be useful in when estimating costs for budgeting purposes, or when evaluating how farmers will respond to the policy. / Master of Science

As one of the largest and most productive estuaries in the United States, the Chesapeake Bay is a great economic, ecological, and cultural asset to the Mid-Atlantic region. Excess nitrogen and phosphorus discharge, however, has contributed to reduced levels of dissolved oxygen in various locations throughout the Bay. In 2010, the EPA developed a Total Maximum Daily Load (TMDL) for the entire watershed that established nutrient reduction targets to achieve Bay water quality objectives. The TMDL required states in the Chesapeake Bay watershed to create implementation plans to meet nutrient reductions. Maryland and Virginia specifically established stringent point source regulatory policies designed to meet point source reduction targets. Point source control programs created financial incentives for reducing nutrient discharge beyond regulatory requirements. This thesis will examine the extent to which Maryland and Virginia wastewater treatment plants undertake operational improvements to increase nutrient removal in response to state program incentives. Through quantitative and qualitative analysis, this thesis found evidence of lowered nitrogen discharges in response to financial incentives presented by each states point source control programs at municipal wastewater treatment plants. Maryland achieves modest improvements at a subset of advanced treatment WWTPs as a result of financial incentives presented by the state's public subsidy program. Although Virginia advanced treatment plants operating within a nutrient trading program have little incentive to over-comply, there is some evidence of operational improvements at less advanced nitrogen removal plants / Master of Science

Increased water scarcity due to changing climate, population growth, and economic development is a major threat to the sustainability of irrigated agriculture in the Western United States and other regions around the world. Management practices, such as controlled deficit irrigation, that seek to maximize the productivity of a limited water supply are critical. When using controlled deficit irrigation, remote sensing of crop canopy temperature is a useful tool for assessing crop water status and for more precise irrigation management. However, there is potential that nutrient deficiencies could compound the interpretation of water status from leaf temperature by altering leaf color and radiation balance. One objective of this thesis was to evaluate whether nitrogen fertility status of maize interacts with remotely sensed leaf temperature under full and limited irrigation. Another objective was to evaluate the effect of varying irrigation and nitrogen regimes on three water stress indices: Crop Water Stress Index (CWSI), Degrees Above Non-Stressed (DANS), and Degrees Above Canopy Threshold (DACT). Replicated studies were conducted using maize grown in both the glasshouse and the field. The glasshouse study consisted of combinations of well-watered and drought irrigation and sufficient and deficient nitrogen levels, while the field study consisted of combinations of well-watered, limited or controlled deficit, and drought irrigation and sufficient, sufficient delayed, and deficient nitrogen levels. In the glasshouse, leaf chlorophyll content was reduced moderately by limited irrigation and more so by N deficiency. For most observations in the glasshouse, the remotely sensed leaf temperatures were affected by irrigation, but not by N level. With drought irrigation, leaf temperature averaged 29.0° C, compared to 27.9 °C for the well-watered treatment. Similar results were observed in the field, illustrating the utility of canopy temperature in detecting water stress and that the measurement was not confounded by N status. It was also found that irrigation had a significant effect on all three water stress indices. For example, in the glasshouse, cumulative DANS was 32.2 for the drought treatment and 15.5 for the well-watered treatment. Similar results were found for other stress index measurements both in the glasshouse and the field. DANS underestimated stress on days when the reference crop was stressed and overestimated stress on low temperature days. DACT risks finding no stress when temperatures are below the canopy threshold temperature of 28.0 °C. Thus, CWSI is the most effective index, given that it takes humidity and air temperature into account. Indices were only weakly related to leaf area, biomass or grain yield, or crop water productivity. Linear regression of Nitrogen Sufficiency Index and its effect on crop growth found significant effects on biomass and grain yield, crop water productivity, and final leaf area. Thus, water stress indices are useful tools in evaluating crop water status, but consideration of other factors, such as nutrient status, must be taken for prediction of crop growth and yield.

Managing nitrogen (N) and phosphorus (P) in agricultural systems in the Mid-Atlantic is an important practice due to environmental and economic concerns. The objectives of the experiments reported in this dissertation were: (1) evaluate irrigation via evapotranspiration (ET) calculations for fresh market tomatoes grown using polyethylene mulch; (2) determine optimum N application method and rate for fresh market tomatoes; and (3) evaluate changes of soil P pools from applications of poultry litter (PL), PL amended with alum (PLA), triple super phosphate (TSP), and no P fertilizer in a long-term no-till corn-wheat-soybean rotation. A calculated irrigation rate, based on 30-year average historical weather data, of 0.5ET provided sufficient irrigation for optimum tomato yields in near average climactic seasons. Utilizing a tensiometer in a warmer and drier season than average protected against under-irrigation rates for fresh market tomatoes. Nitrogen applications ranging from 200 to 242 kg N ha-1 using a combination of a banded method, incorporation, and fertigation produced optimum tomato yields while significantly reducing residual post-harvest inorganic soil N compared to higher N fertilizer rates. The incorporated only method resulted in crop loss and reduced yields with N fertilizer rates greater than 224 kg N ha-1 in the unseasonably hot and dry season. Applications of PL and PLA to no-till land on a N basis significantly increased Mehlich-1 extractable P and 1 M NH4Cl extractable P (loosely bound P) in shallow (0-5 cm) soil samples compared to 0-P control and TSP treatments. However, alum additions in PLA significantly reduced loosely bound P compared to soils fertilized with non-amended PL in shallow soil samples. Overall, results from these studies offer insight into production practices that increase profitability and environmental stewardship in fresh market tomatoes by optimizing fertilizer and irrigation use while maintaining marketable tomato yields. Additionally, PLA reduced the amount of loosely bound P in 0-5 cm soil samples that could potentially move to surface water in these coarse textured soils. / Ph. D.

Increasing awareness of hypoxia in coastal marine regions across the globe has led to creation of nutrient reduction strategies to protect water resources and organisms living in affected waters. In the Mississippi River Basin, the Governor’s Action Plan has called for a 45% load reduction of both, total nitrogen (N) and total phosphorus (P), to reduce the Gulf of Mexico hypoxic zone to a manageable size. Objectives of this dissertation aimed to determine nutrient reduction efficiencies of low-grade weirs, and to evaluate abundance and composition of microbial communities involved in key processes of denitrification following low-grade weir implementation in the Mississippi Delta. Results of this dissertation evidenced the efficiencies of low-grade weirs to reduce nutrient runoff to downstream waters as a viable BMP. Average median load reductions in N, P, and sediment of -5%, 23%, and 29%, respectively, were determined in ditches with low-grade weirs. Results highlighted more efficient reductions in P and sediment, and greater variability in N reductions during storm events, prompting management considerations toward BMP successes and limitations. Valuable insight towards seasonal nutrient fluxes in agricultural runoff due to spring fertilizer applications, increased rainfall patterns in the winter and spring, and drying-wetting cycles, was also evidenced by the data collected. It was determined that utilizing a three-scale sampling regime was most effective for capturing patterns of microbial community abundance and composition in ditches with low-grade weirs. Preliminary evidence towards weir proximity influencing microbial community abundance, and relationships between microbes and soil carbon and N was also found. Utilizing the three-scale sampling regime, microbial communities in multiple drainage ditches, with and without weirs, were investigated. Outcomes showed that weirs increased soil moisture, which subsequently increased functional gene abundance of 16S rRNA and nirS. Furthermore, weir implementation and associated constructions were not found to directly influence microbial community diversity, abundance, or chemical parameters. Results from this dissertation support the potential benefits of weirs to create suitable environments to physically reduce P and sediment loads and for denitrifying microbes to remediate N from agricultural runoff.

This study provides an environmental and economic analysis of the ability to reduce potential nitrogen loadings to water bodies through the implementation of nutrient management plans on livestock farms. Study results indicate that nutrient management plans do result in significant reductions while maintaining or increasing farm income. Nutrient management plans on the four case farms reduced mean nitrogen losses by 23 to 45 percent per acre while increasing net farm income from $395 to $7,249. While reducing excess nitrogen applications with the implementation of nutrient management plans achieved significant reductions in potential nitrogen losses, further reductions may be achieved through farm level planning. After achieving initial reductions through the elimination of excessive nutrient applications, variation in application rates of organic and inorganic fertilizers across soils may become important in achieving further reductions in nitrogen loss. Study results suggest that it may be beneficial to apply higher rates of manure on soils and slopes less susceptible to nitrogen losses in order to reduce applications elsewhere. Increased nutrient losses on such fields may be more than offset by reductions on soils more susceptible to nutrient losses. Linear programming results for the Shenandoah Valley Dairy show that nitrogen losses could be reduced up to 44 percent below pre-plan losses with no impact on farm net economic returns. However, if nitrogen loss restrictions were instituted beyond this level, the impact on farm income increases significantly. After-plan nitrogen losses can reduced up to 52 percent, but farm returns decrease by 56 percent. / Master of Science

Nonpoint Source (NPS) pollution, pollution that comes from diffuse sources that are difficult to trace back to a single point such as farm fields, is a major concern affecting America's water ways. Nationally, agriculture is the leading source of water impairment and has also been identified as the largest source of pollution affecting the Chesapeake Bay. There are proposals now for a program that would pay farmers to use 15 percent less than the extension recommended amount of fertilizer. Known as the Yield Reserve Program, or Enhanced Nutrient Management, this policy could possibly help to reduce the nutrient loads. The objective of this study was to evaluate the effects of a Yield Reserve Program on farm yields and net revenues. Costs were estimated for different policy implementations for the Virginia Coastal Plain to better understand problems with this type of program. The effects of Yield Reserve on enterprise net returns, yields, and N applications for corn under varying weather and soil conditions were estimated. Based on experimental trials from North Carolina and Virginia from 2000 to 2004, yield response functions were calculated for corn. The costs of the Yield Reserve Program vary depending on its implementation, but under current proposals these costs were estimated at $113 per hectare, and $10,855,000 for the coastal plain. This proposal is a more costly program than would be necessary to compensate farmers for yield losses based on estimates in this study. / Master of Science