Nitrogen (N) fertilizer is a required mineral nutrient in containerized crop production that is necessary for crop growth and development. Due to production aspects, the N added to crops far exceeds the amount that the plant uses and such inefficiency results in adverse environmental impacts related to N gaseous and aqueous emissions from containers on the production site. Growers are responsible for optimizing nutrient usage in crop production. Three studies were conducted to investigate and better understand the fate of applied N fertilizers, the transformations associated with individual N sources, and the influence of substrate texture on losses of aqueous and gaseous N species. The first study conducted a mass balance looking at the four major avenues of N fate in an open-air container production setting (plant uptake, immobilized or bound N in a pine bark substrate, leached aqueous N, and gaseous emissions of N), the mass balance was speciated to measure applied and intermediary forms of N fertilizer species to provide insight into the overall fate of applied N. Show Off® Forsythia ×intermedia' Mindor' were grown using two control-release fertilizer (CRF) treatments [AN (ammonium-nitrate based) or UAN (urea ammonium-nitrate)] products. This study determined that 97% of the released N from the CRF treatments was lost via aqueous or gaseous pathways. The aqueous losses were inferred to be predominately composed of NO3-N, while the gaseous emissions were inferred to be predominately lost as inert nitrogen gas (N2). During a second experiment, individual N sources treatments [urea (CH4N2O), ammonium (NH4+), and nitrate (NO3-)] were applied to established containers of At LastⓇ Rosa x 'HORCOGJIL' grown in a pine bark substrate in either open wall high tunnel or a glass greenhouse to determine subsequent reaction sequence and fate based on applied N source. By applying an individual form of N it was determined that based on the N source applied, a sequential set of reactions occurs based on the N source. This study determined that the reactive N gaseous species occurred from the hydrolysis of CH4N2O-N to NH4+ and the nitrification of NH4+ to NO3- and then the denitrification of NO3- to N2. Hibiscus moscheutos' Vintage wine' was grown in either a coarse or fine texture substrate utilizing either a water-soluble fertilizer or a CRF to compare the influence of pine bark texture on N leachate losses and RN gaseous emissions. There were few differences between the two substrate texture treatments related to aqueous or gaseous N losses. In both experiments, the Hibiscus grown in the fine texture substrate resulted in higher above and below-ground biomass at experimental termination. Working with growers to develop best management practices will help to improve the use of N fertilizers and impact growers economically, while simultaneously reducing losses leading to less environmental impact on the areas surrounding production sites. / Doctor of Philosophy / Nitrogen (N) fertilizer is a crucial mineral nutrient input to produce container crops, however excessive application can have detrimental effects on the environment including gaseous N emissions and N leaching leading to water pollution. Therefore, three studies were conducted to investigate N losses during production and potential mitigation strategies using common management practices in the production of container crops. During the first study investigating how N fertilizer is lost from production, results showed that a significant portion of the N added to the containers is either emitted from the containers into the atmosphere or leached from the container. Only a small fraction of the applied N was utilized by the plants for growth and development. The second study investigated the reactions and transformations of different N fertilizers sources. When applying single N sources urea (CH4N2O), ammonium (NH4+), or nitrate (NO3-) result in a set of sequential reactions that occur based on the applied N source. Urea is hydrolyzed via CH4N2O hydrolysis leading to the formation of NH4+ which is nitrified via nitrification to NO3- which is denitrified via denitrification leading to the production of N2 gas. In the final study two pine bark substrate classes were compared when using either a water-soluble fertilizer (WSF) or a controlled-release fertilizer (CRF). Surprisingly there were only a few differences between the two substrate treatments in either the WSF or CRF studies. This body of work show the importance of investigating N fertilizer usage in container crop production. Collaboration between researchers and growers is crucial to develop management practices that maximize the associated economic input of N fertilizers and minimize losses of N that are detrimental to the environment.

Spectral reflectance-based, remote sensing technology has been used to adjust in-season nitrogen (N) fertilizer rates for wheat to account for spatial variability in grain yield potential at a sub-meter resolution. The objective of this study was to examine the relationships among spectral reflectance indices, corn tissue N content, chlorophyll measurements, plant size and spacing measurements, and grain yield to develop a similar strategy for variable-rate N management in corn. Irrigated and non-irrigated studies were conducted during the 2002 and 2003 growing seasons in eastern Virginia. Plots were treated with various rates of preplant, starter, and sidedress N fertilizer to establish a wide range of grain yield potential. Spectral measurements, tissue N, chlorophyll measurements, and plant physical measurements were collected at growth stages V6, V8, and V10. At maturity, grain yield was determined and correlated with in-season data and optimum N rate to calibrate in-season, variable-rate N fertilization strategies. Results from these studies indicate that spectral reflectance is well correlated with plant N uptake and chlorophyll meter readings and can also be correlated with final grain yield. These relationships may be used to develop a model to predict in-season, variable N application rates for corn production at a sub-meter resolution. / Master of Science

Nitrogen is the most frequently limiting nutrient in southern pine plantations.  Previous studies found that only 10 to 25% of applied urea fertilizer N is taken up by trees.  Enhanced efficiency fertilizers could increase tree uptake efficiency by controlling the release of N and/or stabilize N.  Three enhanced efficiency fertilizers were selected as a representation of fertilizers that could be used in forestry: 1) NBPT treated urea (NBPT urea), 2) polymer coated urea (PC urea), and 3) monoammonium phosphate coated NBPT treated urea (MC NBPT urea). Urea, MC NBPT urea, and NBPT urea fertilizer treatments showed an extractable NH4+ spike 14 days after fertilization while the polymer coated urea showed a spike in NH4+ 49 days after fertilization. Total ecosystem recovery of fertilizer in each treatment was; MC NBPT urea, 51.29 g N; NBPT urea, 48.87 g N; urea, 45.09 g N; and PC urea, 31.30 g N which represents 78.7%, 74.7%, 72.1%, and 47.6% respectively of the total N applied.  For the MC NBPT urea, NBPT urea, and PC urea treatments the largest sinks for N were the forest floor and mineral soil.  The largest sink for fertilizer applied N in the urea treatment was in the tree.  The 2011 foliage cohort was the largest sinks for fertilizer N recovered by the tree.  N volatilization was around 20% for all fertilizer treatments except polymer coated fertilizer, which was 1.1%.  Urea preformed the same as the soluble enhanced efficiency fertilizers and better than the PC urea fertilizer.  The results emphasize the importance of climatic conditions on fertilizer release and effectiveness. / Master of Science

Best management practices (BMPs) are used in the nursery and greenhouse industry to increase production efficiency, and also serve to help meet clean water limitations on contaminants entering waters such as the Chesapeake Bay Watershed. Research is lacking on which BMPs are most widely used or most efficacious for Virginia nursery and greenhouse growers. Objectives of this work were to determine BMP use, barriers to adoption, and scientific efficacy. We conducted a survey of Virginia growers to find the 1) most widely used BMPs, 2) reasons behind BMP use, and 3) any barriers to BMP adoption. Sixty growers (17%) responded to the survey. The most widely used BMPs included irrigation scheduling, integrated pest management, optimized irrigation efficiency, plant need based watering, grouping plants by water needs, on-site water capture and collection, and use of controlled-release fertilizers (CRFs). Cost was a barrier to BMP adoption, and environmental concern was a commonly reported reason for BMP use. We documented the science supporting selected water-related BMPs (grass buffer strips, CRFs, and irrigation optimization BMPs). Providing the science supporting BMP use gives growers confidence in implementing BMPs to limit water contamination, and prevent waste. / Master of Science / Best management practices (BMPs) are used in the nursery and greenhouse industry to increase production efficiency, and also serve to help meet clean water limitations on contaminants entering waters such as the Chesapeake Bay Watershed. Research is lacking on which BMPs are most widely used or most efficacious for Virginia nursery and greenhouse growers. Objectives of this work were to determine BMP use, barriers to adoption, and scientific efficacy. We conducted a survey of Virginia growers to find the 1) most widely used BMPs, 2) reasons behind BMP use, and 3) any barriers to BMP adoption. Sixty growers (17%) responded to the survey. The most widely used BMPs included irrigation scheduling, integrated pest management, optimized irrigation efficiency, plant need based watering, grouping plants by water needs, onsite water capture and collection, and use of controlled-release fertilizers (CRFs). Cost was a barrier to BMP adoption, and environmental concern was a commonly reported reason for BMP use. We documented the science supporting selected water-related BMPs (grass buffer strips, CRFs, and irrigation optimization BMPs). Providing the science supporting BMP use gives growers confidence in implementing BMPs to limit water contamination, and prevent waste.

published_or_final_version / Botany / Master / Master of Philosophy

No description available.

Durum grain quality is affected by many factors, but water and nitrogen are factors that the grower can control. The purpose of this research was to determine 1) the nitrogen application rate required at pollen shed to maintain adequate grain protein levels if irrigation is excessive or deficient during grain fill and 2) if nitrogen applications during grain fill can elevate grain protein. Field research was conducted at the Maricopa Agricultural Center using the durum varieties Duraking, Minos, and Turbo. The field was treated uniformly until pollen shed when nitrogen was applied at rates of 0, 30, and 60 lbs /acre. During grain fill, the plots were irrigated based on 30, 50, or 70% moisture depletion. In a separate experiment, nitrogen fertilizer was applied at a rate of 30 lbs N /acre at pollen shed only, pollen shed and the first irrigation after pollen shed, and pollen shed and the first and second irrigation after pollen shed. Increased irrigation frequency during grain fill decreased HVAC from 93 to 81%. Increasing nitrogen rate at pollen shed from 0 to 30 and 30 to 60 lbs N /acre increased protein from 11.6 to 12.5% and 12.5 to 13.3% and increased HVAC from 79 to 89% and 89 to 94 %. Nitrogen fertilizer application at the first irrigation after pollen shed increased grain protein content from 12.9 to 13.6% and application at the first and second irrigation after pollen shed increased grain protein content further to 14.1% averaged over varieties. Nitrogen fertilizer application during grain fill may not be too late to increase grain protein content.

Research conducted recently suggested that application of nitrogen fertilizer from flowering until the dough stage could increase grain protein concentration in durum even if nitrogen applications earlier in the season were adequate for optimum yield. We tested the ability of late season nitrogen application to increase protein at commercial farms in Buckeye, Casa Grande, and Vicksburg. Late season nitrogen increased protein by nearly two percentage points in two out of the three locations. No response was measured at the third location possibly due to high rates or nitrogen earlier in the season. The cost of the late season fertilizer at 35 to 50 lbs N /acre was about $15 /acre. The fertilizer was paid for at the two location where a response was obtained by 1) the slight yield increase of 310 lbs /acre which was worth about $23 /acre and 2) the difference in dockage or premiums paid for protein which was worth about $38 /acre. It is possible that lower stem nitrate levels could be used to determine whether or late applications of nitrogen will increase protein, but we currently do not have a method to determine if protein will be over the critical level of 13% or if HVAC will be over the critical level of 90 %.

Nitrate content of the lower stem tissue of small grains is used as a guideline for nitrogen fertilization. The turnaround time for nitrate analysis in a commercial lab is usually 1 to 3 days. Nitrate quick tests have been suggested as a means of obtaining results on a more timely basis. The quick tests analyze nitrate in the sap or juice squeezed out of the tissue. A nitrate test conducted by a commercial lab is performed on the dried and ground tissue. In this study, I found that the quick tests on plant sap are not as accurate as conventional tests on dried tissue since the moisture content of the fresh plant tissue varies depending on its nitrate content and the growth stage of the plant. We compared the following quick test methods: nitrate test strips, a colorimetric procedure, and a hand held nitrate electrode. Nitrate test strips were not sensitive enough to be useful and were difficult to compare to the color charts. An electronic strip reader could alleviate this difficulty and make the strips a viable option. Colorimetric procedures, or those that rely on nitrate producing a colored solution with certain chemicals added, are not adapted to analyzing plant sap since the green color and organics in the sap interfer with the color produced by the nitrate. The hand held nitrate electrode, or Cardi meter, was the simplest and most accurate method we experimented tested. Quick tests for nitrate in the sap have the following disadvantages: 1) It is not easy to squeeze the sap out of the plant tissue, 2) The sap needs to be diluted to fit into the analytical range of the test, and 3) The moisture content of the tissue needs to be accounted for somehow for the results to be most accurate.

Soil tests were developed in the 1930's as a guideline for phosphorus fertilizer application. The phosphorus soil test for the calcareous soils in the Western U.S. is based on bicarbonate extraction and is often called the Olsen P method. Phosphorus fertilizer recommendations for small grains based on this test are remarkably similar across the Western states. Despite the availability of this test, its proven accuracy (93% in California), and its low cost ($1 /acre), most farmers in Arizona apply phosphorus fertilizer to their small grains crops without the benefit of a preplant soil test. The purpose of this study was to demonstrate the effectiveness of the soil test in predicting a response to phosphorus fertilizer. At Maricopa, the soil test P was 8.1 ppm, a variable response to P fertilizer was expected, and a variable response to P fertilizer was obtained. We were able to detect a response to P fertilizer at this site with only 1 out of 4 varieties, and the response averaged across varieties was 336 lbs /acre or a 6% increase. No response to P fertilizer was obtained on a commercial farm in Buckeye where the soil test P was 22 ppm and a response was not expected. At the Yuma-Mesa site, the preplant P level was also 22 ppm, and a yield increase of29% (1442 lbs /acre) was measured on barley even though a response was not expected. The soil on the Yuma -Mesa is 95% sand and perhaps the soil test for P needs to be adjusted for this soil type, but at the other sites tested, the current soil test recommendations for P seem to be accurate.