This study investigated a potentially sustainable rice production system in the Mississippi Alluvial Valley (MAV) that uses ecological principles to enhance environmental quality at the field scale. It was hypothesized annual flooding of rice fields to create waterbird habitat would benefit soil health, providing agronomic benefits to the farmer. Two sites were selected: a low-external-input-sustainable-agriculture (LEISA) system with flooded (LF) and nonlooded (LN) fields and a conventional site with flooded (CF) and nonlooded (CN) fields. Soil microbial diversity and nutrient content were quantified and compared. Camera traps were used to document bird activity for estimates of fecal matter input. Soil health variables linked LF high bird activity with soil health and pathogen detection. Evidence from the investigation provided a framework for other producers within the MAV to adopt similar management methods, ultimately improving the overall integrity of soil, water, and environmental quality.

Natural selection should favor selective foraging in deer to choose among nutrients in plant communities to meet their physiological requirements. I designed a two-tier cafeteria-style experiment where I measured plant nutritional quality and white-tailed deer (Odocoileus virginianus) use on 1) 15 species of herbaceous plants, and 2) 2 species of plants of manipulated nutrient concentrations. I tested the hypotheses: 1) deer use across plants would be influenced by plant nutrients, and 2) soil nutrients would influence plant selection by deer. My analyses indicated deer selected plants of low neutral detergent fiber and sulfur concentrations. However, deer selected for crude protein. I also confirmed soil nutrients indirectly influenced diet selection. Nutrient augmentation altered phosphorus concentrations within plants, and plant phosphorus concentration explained 47% of the variation in diet selection. My data indicated deer use both nutrient maximization and avoidance to balance diet selection and plants mediate the indirect effects of soil nutrients availability on herbivore diet selection.

Nitrogen and phosphorus have individually or jointly been demonstrated to limit primary productivity in most of Earth’s forested systems. Nutrient limitation of forest primary productivity is important because terrestrial systems currently store large amounts of carbon and partially mitigate carbon dioxide emissions from anthropogenic activities. There is also evidence that nutrient availability relative to demand is decreasing in forested systems. Trees have complex responses to nutrient availability, including changes in allocation of nutrients to different organs and mechanisms that aide in recycling of nutrients within the plant and ecosystem. In this work I provide new insight related to nutrient allocation and conservation mechanisms in trees, demonstrating that these mechanisms affect nutrient limitation of primary productivity. In Chapter 2, I provide evidence that tree reproductive organs have nutrient resorption processes that transfer nutrients from fruit to seeds and I also demonstrate that tree fruit are capable of photosynthesis – in the absence of such processes the carbon and nutrient costs of tree reproduction would likely be higher. In Chapter 3, I report on the results of a community science project through which I identified variation in biogeochemically relevant leaf traits across much of the geographic distribution of Acer rubrum, one of North America’s most broadly distributed tree species, demonstrating that foliar nitrogen resorption is highest in colder high latitudes and leaf litter %N is highest at warmer low latitudes. In Chapter 4, I compare leaf and reproductive litterfall nitrogen and phosphorus metrics worldwide and demonstrate that reproductive litterfall is a significant contributor to tree nutrient budgets, comprising a median of 13.0% and 16.1% of nitrogen and phosphorus fluxes, respectively, when combining leaf and reproductive litterfall. Overall, the results of my dissertation enable me to identify several understudied aspects of tree nutrient allocation and conservation processes by considering the biogeochemistry of reproductive and foliar organs and associated variation across the natural distribution of trees.

Soybean [Glycine max (L.) Merr.] biomass and yield has increased over the past several decades in the midsouthern United States; therefore, a better understanding of the nutrient requirements of the crop is needed. Nutrient uptake and partitioning in soybean is fundamental to understanding the physiology of nutrient accumulation relative to crop yield. Technological advances and improved management strategies in soybean production have contributed to significant yield increases. Research was established in 2017 and 2018 in Stoneville, MS, to evaluate soybean nutrient uptake and partitioning across multiple soybean cultivars and two planting dates. Coarse- and fine-textured soils commonly cropped in Mississippi under furrow irrigation were utilized. Soybean total aboveground biomass was collected at multiple growth stages, including V4, R2, R5.5, R6.5, and R8. At reproductive stages R5.5 to R8, soybean aboveground biomass was partitioned into senesced leaves, pods, and seeds. All biomass components were analyzed for content of primary macronutrients. Two soybean cultivars for each of four herbicide-resistant technologies were selected to represent subplot treatments. The greatest yield was produced by dicamba- and glyphosate-tolerant HT, followed by glufosinate tolerant, followed by conventional HT. Soybean planted in April produced grain yield greater than May planted soybean. Averaged across four site years, field removal of total N, P2O5, and K2O partitioned into the seed at physiological maturity was approximately 175 kg N ha-1, 33 kg P2O5 ha-1, and 120 kg K2O ha-1.

The Lake Clearwater catchment, in the Canterbury high country of New Zealand, has a native ecosystem that is adapted to low nutrient conditions. Wetlands in the catchment are identified by the Department of Conservation’s Arawai Kākāriki Wetland Restoration Programme as one of three important endemic wetland types in New Zealand. Uncertainty regarding diffuse nutrient load from agriculture into the lake and wetland ecosystems is limiting effective management of the catchment. This study investigated hydrological processes and nitrogen and phosphorus concentrations to improve knowledge of the sources, characteristics and magnitude of nutrient loading from agricultural land use in this 46 km2 high country catchment. Relevant hydrological data and literature pertaining to the catchment was extensively reviewed. In addition, flow for five key surface waterways was continuously logged at ten sites for 2 years. Concurrently, nutrient concentrations for total nitrogen, nitrate, ammoniacal nitrogen, total phosphorus and dissolved reactive phosphorus were measured at ten surface water sites and three groundwater sites. Total nitrogen and phosphorus load from farmland was calculated from annual flow and median concentrations for four waterways: farmland perennial stream runoff, farmland ephemeral stream runoff, a wetland channel below the farmed hillslope and the lake outlet. Similarly, total nitrogen and phosphorus load for unfarmed land was calculated from the flow and median concentration of two un-impacted perennial streams. Total nitrogen and phosphorus mass balances were calculated and used to estimate subsurface nutrient load and runoff volume from the farmed hillslope. Estimates of subsurface runoff were also made using Darcy’s equation and a water balance. Nutrient load predictions from the Catchment Land Use for Environmental Sustainability (CLUES) model were compared to measured loads. Nutrients were found to be elevated downstream of farmland, especially nitrogen, which was often above relevant guidelines and typical concentrations in upland waterways in Canterbury. Nitrate in farmland subsurface runoff was elevated and was estimated to contribute 52% of total nitrogen yield from farmland. Total nitrogen yield (1.96-2.94 kg ha-1 year-1) for farmed land was comparable to minimum values for pastoral land use in literature but total phosphorus yield (0.093-0.123 kg ha-1 year-1) was well below published values. The range in yield estimates is due to subtraction of a high and a low estimate of natural baseline yield from the measured in-stream yield. Total nitrogen export from the lake (2518 kg year-1) was greater than estimated input (1375 kg year-1) from farmed and non-farmed land indicating an additional source of nitrogen into Lake Clearwater. Total phosphorus export from Lake Clearwater of 58 kg year-1 was 24% less than total estimated loads into the lake (76 kg year-1) from farmed and non-farmed land. Phosphorus was not often above relevant guidelines and the median total nitrogen to total phosphorus ratio in Lake Clearwater (49:1) indicated phosphorus is the limiting nutrient in the lake. Because phosphorus was less elevated relative to nitrogen, an increase in phosphorus inputs could have a greater effect on productivity in the wetland and lake. With corrected land use information, total nitrogen loads predicted by the CLUES model were reasonable but total phosphorus loads were greatly overestimated. Investigation into potential impacts of the elevated nutrient loads described in this study on receiving native ecosystems is recommended to inform conservation efforts.

Three separate food grouping systems were derived for diet evaluation by utilizing a computer clustering program. System 1 was based on grouping of foods according to nutrient quality and quantity, system 2 was based on nutrient quality and frequency of consumption and system 3 was based on nutrient quality and kilocalories consumed. Defendable nutritional principles as well as knowledge of present nutritional concerns and eating habits of the U.S. population underpinned the derivation of the three systems. Over 4,000 individual foods were condensed to approximately 325 groups. The three food grouping systems which were developed were compared for accuracy by calculating nutrients for a mean daily food record for a random sample of 126 adults in the National Food Consumption Survey. Percent error for each of 15 nutrients was calculated for each derived system as contrasted to the value which resulted from using individual nutrient values for discrete foods. In evaluating the 3 systems the most accurate comparison resulted from the system which was based on frequency of consumption. The results of the comparison indicated that 11 of the 15 nutrients which were determined were consistent in all systems. The exceptions were vitamin A, vitamin B12, riboflavin and ascorbic acid. These inconsistencies can be attributed to the nature of the food sources and the nutrients themselves. It was demonstrated that fortified foods and food supplements which contain varying amounts of selected nutrients require individual treatment for accurate analysis. These results supported the hypothesis that a shortened dietary analysis system can be used without compromising accuracy.

Biochars are the product of high temperature treatment of carbonaceous materials with little or no oxygen present, termed “pyrolysis”. Biochars derived from the pyrolysis of biomass feedstocks have proven effective amendments on highly weathered tropical soils. However less is known about their impact on temperate soils and associated crop growth. Moreover, there is inadequate knowledge of the impacts of different biochars produced from different feedstocks under differing pyrolysis conditions. Therefore, a study was conducted to evaluate the effectiveness of different biochars as amendments to improve soil conditions for crop growth, with emphasis on soil fertility and crop nutrition impacts. The response of canola-wheat in rotation to five biochars was evaluated in controlled environment and field experiments conducted on Brown and Black Chernozem soils over a two-year period. Treatments were biochar added at 1 and 2 t ha 1 without and with nitrogen (N) and phosphorus (P) fertilizers at 50 or 100 kg N ha 1 and 25 kg P2O5 ha 1. Parameters evaluated were crop biomass and grain yield, N and P uptake, % recovery of applied N and P, residual soil nutrients (NO3 N, and PO4+ P), pH, electrical conductivity (EC), % organic carbon (% OC) and gravimetric soil moisture. Biochar application resulted in significant increases (p<0.05) in canola yield compared to the control for two fast pyrolysis biochars originating from wheat and flax straw added to the Black Chernozem soil in both studies. No significant response was observed for any of the biochars on the Brown Chernozem. Slow pyrolysis biochar derived from willow feedstock appeared less effective did not show any significant response. Occasional depressions in crop yield were observed in both crops with both soils. In these calcareous Chernozems, biochar did not greatly alter the N and P availability, and its effects on soil pH, % OC, EC and moisture content were small and often non-significant. These results suggest that biochar applications at 1 2 t ha 1 to prairie Chernozemic soils will not have large effects on soil properties or plant growth. Higher rates of application will require development of application technology due to the dusty, powdery nature of the biochar material.

A floating treatment wetland (FTW) is an ecological approach which seeks to reduce point and nonpoint source pollution by installing substrate rooted plants grown on floating mats in open waters. While relatively novel, FTW use is increasing. A review of literature identified several research gaps, including: (1) assessments of the treatment performance of FTWs; (2) evaluations of FTWs in the U.S., particularly within wet ponds that receive urban runoff; and (3) plant temporal nutrient distribution, plant growth rate, and the long-term persistence of the FTWs in temperate regions with periodic ice encasement. An assessment model, i-FTW model, was developed, and its parameter s fitted based on data from 14 published FTW studies in the first research topic. The estimated median FTW apparent uptake velocity with 95% confidence interval were 0.048 (0.018 - 0.059) and 0.027 (0.016 - 0.040) m/day for total phosphorus (TP) and total nitrogen (TN), respectively. The i-FTW model provided a more accurate prediction in nutrient removal than two common performance metrics: removal rate (mg/m2/day) and removal efficiency (%). In the second research topic, the results of a mesocosm experiment indicated that FTWs with 61% coverage, planted with pickerelweed (Pontederia cordata L.) or softstem bulrush (Schoenoplectus tabernaemontani), significantly improved TP and TN removal efficiency of the control treatment by 8.2% and 18.2%, respectively. The pickerelweed exhibited significantly higher phosphorus and nitrogen removal than the softstem bulrush when water temperatures were greater than 25 deg C. Field observations in the third research topic found that pickerelweed demonstrated higher phosphorus removal performance (7.58 mg/plant) than softstem bulrush (1.62 mg/plant). Based on the observed seasonal changes in phosphorus distribution, harvest of above-ground vegetation is recommended to be conducted twice a year in June and September. Planted perennial macrophytes successfully adapted to stresses of the low dissolved oxygen (DO) concentrations (minimum: 1.2 mg/L), ice encasement, and relatively low nutrient concentrations in the water (median: 0.15 mg/L TP and 1.15 mg/L TN). Systematic observation of wildlife activities indicated eight classes of organisms inhabiting, foraging, breeding, nursing, or resting in the FTWs. Recommendations for FTW design and suggestions for further research are made based upon these findings. / Ph. D.

No description available.

No description available.