<p>Few contemporary studies have examined nutrient accumulation and partitioning of modern corn (Zea mays L.) hybrids grown under in-season sulfur (S) and potassium (K) nutrient management. A fertilizer x hybrid field experiment was conducted during the 2020 and 2021 growing seasons in West Lafayette, Indiana to (1) determine the efficacy of in-season fertilizer management as a strategy to increase grain yield among different modern hybrids, (2) determine the extent to which nutrient harvest index (NutHI) relates to other plant traits under intensive agronomic management, and (3) determine whether grain yield and within-plant nutrient dynamics respond to in-season S and K management differently depending on hybrid. The three fertilizer treatments (whole plot) were (1) Control, no S or K applied, (2) Sulfur, 22.4 kg S ha-1 broadcast applied as ammonium thiosulfate (ATS) [12-0-0-26S] immediately after planting, and (3) Sulfur_Potassium, S (from treatment 2) plus 108 kg K ha -1 topdress applied via Aspire™ [0-0- 58(K2O)-0.5B] at the V4 growth stage. The experiment consisted of four modern Pioneer® corn hybrids (subplot) that varied in crop relative maturity (CRM) from 105 to 114 days planted at the same density following fall strip tillage in a continuous corn production environment. Aboveground dry matter accumulation (DM) and plant tissue concentrations of N, P, K, S, and B were measured via whole-plant samples at V6, R1, and R6. Soil K levels were above the critical K level prior to K application but soil S was not reliably determined. </p> <p><br></p> <p>Grain yields following Sulfur and Sulfur_Potassium treatments were similar, averaging 14.6 Mg ha-1 , which represented a 20% increase over the 12.2 Mg ha-1 observed in the Control. Grain yield gains following S application were the result of increased S uptake, first detected at V6, which alleviated S-deficiency and improved the N to S ratio (N:S) within the plant. K application did not affect grain yield. The greatest contrast in grain yield among hybrids corresponded to extremes in CRM, from 12.9 Mg ha-1 in 105_day to 14.5 Mg ha-1 in 114_day. Fertilizer x hybrid interactions were rarely observed among measured variables with the notable exception of HI, which was increased in later maturity hybrids (111_day and 114_day) by Sulfur and Sulfur_Potassium relative to Control, but was unaffected by fertilizer treatments in 105_day and 110_day hybrids. Most phenotypic parameters were positively influenced by Sulfur and Sulfur_Potassium relative to Control, including above-ground dry matter accumulation (DM), nutrient accumulation, dry matter harvest index (HI), nutrient harvest index (NutHI), and 13 grain/stover nutrient concentrations at maturity. Compared to Control, total plant DM was increased following Sulfur and Sulfur_Potassium by an average of 14% at V6, 16% at R1, and 20% at R6. Whole-plant biomass totals were similar between Sulfur and Sulfur_Potassium, averaging 693 kg DM ha-1 at V6, 10909 kg DM ha-1 at R1, and 26170 kg DM ha-1 at R6; however, K application increased the proportion of total DM partitioned to stover rather than grain, which reduced HI from 0.58 under Sulfur to 0.56 under Sulfur_Potassium. </p> <p><br></p> <p>Nutrient accumulation (of N, P, K, S, and B) was influenced by in-season S and K application at all growth stages relative to the Control. Sulfur application increased V6 wholeplant S and K concentrations, but lowered P and B concentrations. Applying in-season K boosted V6 N and P concentrations, but temporarily reduced K uptake by 10%. Due to gains from S and K application in both DM and nutrient concentration at maturity, total nutrient accumulation in Sulfur_Potassium increased by up to 25% in N, 28% in P, 59% in K, 77% in S, and 44% in B. Total plant DM at maturity was reduced by 14% in the low-yielding 105_day hybrid relative to other hybrids at maturity, leading to similar reductions in nutrient accumulation despite relatively high nutrient concentrations. There was little hybrid variation in whole-plant P, S, and B uptake but substantial hybrid variation in N (9%) and K (21%) uptake. Partitioning of N, P, and K between stover and grain at maturity was influenced by the increased grain nutrient concentrations following Sulfur_Potassium relative to Sulfur. Grain nutrient concentrations under Sulfur relative to Sulfur_Potassium increased from 1.19% N to 1.24% for N, from 0.32 to 0.36% for P, and from 0.39 to 0.44% for K. When Sulfur_Potassium increased grain P and K concentrations over Sulfur, grain nutrient content (i.e., removal) also increased even when grain DM was similar, boosting removal from 48 kg P ha-1 to 54 kg P ha-1 , and from 58 kg K ha-1 to 65 kg K ha-1 . In contrast, grain S and B concentrations, at 0.08% S and 3.3 ppm B, as well as grain contents, at 12.4 kg S ha-1 and 0.05 kg B ha-1 , were similar under both Sulfur and Sulfur_Potassium. As previously stated, NutHI increased substantially in response to both S treatments relative to the Control. The NHI in the Control was just 0.57 versus 0.65 under S treatments while the P harvest index (PHI) was 0.71 versus 0.84, S harvest index (SHI) was 0.50 versus 0.57, and B harvest index (BHI) was 0.35 versus 0.39. Hybrid differences in NutHI were relatively small and were related to both DM and nutrient concentrations at maturity. </p> <p><br></p> <p>While further research is necessary to accurately assess nutrient accumulation and partitioning trends as nutrient management strategies continue to evolve, this study demonstrated 14 that in-season S applications can effectively increase grain yield under S-limiting conditions. Inseason K application did not increase grain yield over Sulfur alone (presumably due to adequate soil K); however, added K still enhanced both grain nutrient removal and NutHI. Furthermore, the influence of plant nutrient concentrations at maturity in both grain (positive) and stover (negative), on NutHI was strongest under fertilizer treatments and NutHI was less dependent on grain yield, total DM, or HI trends. Under hybrid treatments, the influence of nutrient concentrations on NutHI was dependent on DM parameters. While grain yield, DM, and HI were likely to have been contributing factors in NutHI determination, stover nutrient concentration was the most consistent factor related to NutHI across fertilizer and hybrid treatments. The observed variation in NutHI might imply there is still potential for improvement of this index beyond HI alone. Although fertilizer and hybrid treatment responses in whole-plant nutrient concentration were strong during the vegetative period, they were less indicative of NutHI than those at maturity. The positive impact of Sulfur_Potassium on grain nutrient concentration, in the absence of a grain yield response, highlighted a potential disparity between achievable levels of grain nutrient concentration and yield. While in-season nutrient applications can substantially increase grain yields, our results show that in-season fertilizer can also affect nutrient accumulation and partitioning, which are key factors to be considered when making nutrient management decisions. </p>

The overall goal of this research was to improve simulation of soil phosphorus (P) transport and transformations in GLEAMS 3.0, a non-point source model that simulates edge-of-field and bottom-of-root-zone loadings of nutrients from climate-soil-management interactions to assess management alternatives. The objectives of this research were to identify the state of the science for P transport and transformations, determine appropriate relationships for inclusion in GLEAMS, and determine if modifications to GLEAMS improved predictions of P loss in runoff, sediment, and leachate. The state of the science review revealed numerous equations available to predict dissolved P loss in runoff and leachate from a soil's nutrient status. These equations use a single variable to predict P loss and were developed for site-specific conditions based on empirical data. Use of these equations in GLEAMS is not reasonable as transport factors must also be considered when predicting P loss. Results from the sensitivity analysis showed that GLEAMS prediction of leached P were extremely sensitive to changes in the P partitioning coefficient (CPKD). Runoff PO₄-P output was slightly to moderately sensitive, sediment PO₄-P was moderately sensitive to sensitive, and sediment organic P was moderately sensitive to changes in CPKD whereas plant uptake of P was insensitive to slightly sensitive. The weakness of GLEAMS to estimate CPKD has been documented. Upon further investigation, it was determined that CPKD was highly over-estimated in GLEAMS as compared to measured values found during the literature review. Furthermore, this over-estimation caused under-estimation of the P extraction coefficient (BETA P); the value of BETA P remained constant at 0.10 and did not vary over the simulation period. Expressions for CPKD and BETA P were modified in GLEAMS. Data from three published studies (Belle Mina, Gilbert Farm, and Watkinsville) were used in the analyses of three modifications to GLEAMS: GLEAMS BETA P, GLEAMS CPKD, and GLEAMS BETA P+CPKD. GLEAMS BETA P investigated the change in BETA P as a function of soil clay content, GLEAMS CPKD attempted to improve GLEAMS' estimation of CPKD, and GLEAMS BETA P+CPKD assessed the combined effects of changes to BETA P and CPKD. Over the respective study periods, GLEAMS over predicted runoff PO₄-P for Belle Mina by 193 to 238% while under-predicting runoff PO₄-P at Gilbert Farm by 41% and Watkinsville by 81%. Sediment P was over-predicted by GLEAMS for Belle Mina by 225 to 233% and Gilbert Farm by 560%, while sediment P was under-predicted by 62% at Watkinsville. Leached PO₄-P was both over- and under-predicted by GLEAMS; Belle Mina was the only data set with observed leached P values. Simulation results from the model changes were inconclusive. There was no clear evidence supporting use of one model over another. Modifications increased predicted dissolved P in runoff and leachate, while decreasing predicted sediment-bound P in runoff. The original GLEAMS model best predicted runoff and leached PO₄-P at the Belle Mina sites. GLEAMS CPKD was the best predictor of runoff PO₄-P and sediment P at Gilbert Farm. GLEAMS BETA P+CPKD best predicted runoff PO₄-P at Watkinsville. Overall, the proposed improvements to GLEAMS did not improve GLEAMS predictions. In conclusion, GLEAMS should not be used for quantitative estimates of hydrology, sediment, and nutrient loss for specific management practices. As recommended by the GLEAMS model developers, GLEAMS should only be used to predict relative differences in alternative management systems. It is recommended that future research focus on developing a better correlation between CPKD, clay mineralogy and content, and organic matter content, as CPKD has been identified as a vital component of the GLEAMS P sub-model that requires further examination. / Master of Science

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In order to study the influence on blue-green algal nitrogenase activity of environmental variables in deepwater rice-fields (DWR), a laboratory study was planned on a DWR isolate of Calothrix (D764). The variables chosen were light, oxygen, combined nitrogen, phosphorus and iron. As availability of P is likely to play an especially important role for growth and nitrogen fixation in DWR, studies on phosphatase activity of the isolate were also included. The method used for measuring nitrogenase activity was acetylene reduction assay (ARA). In order to convert nitrogenase activity to nitrogen fixation, the conversion ratio of N(_2) : C(_2)H(_2) reduced was determined by comparing the total amount of N fixed with total C(_2)H(_2) reduced. The ratio was 1 : 4.1 and 1 : 5.2 at 85 and 10 µmol photon m(^-2) s(^-1), respectively. Changes in nitrogenase activity in batch culture were studied in relation to growth characteristics. Maximum activity (10.5 nmol C(_2)H(_4) mg d. wt(^-1) min(^-1)) was observed after two days of growth. During this period, juvenile trichomes (hence maximum heterocyst frequency) were abundant and cyanophycin granules were absent; chl a, phycobiliprotein and algal N decreased. It is suggested that the juvenile filament is the most active nitrogen-fixer during the growth of the alga. The response of nitrogenase to changes in light flux (down- or upshift) was rapid. The alga showed a marked drop in nitrogenase activity in the dark, but subsequent changes were slow, with detectable activity after 24 h. Higher nitrogenase activity was observed when the dark grown alga was re-illuminated, than the maximum activity found under continuous illumination. Nitrogen fixation and heterocyst differentiation were suppressed when 10 mg 1(^-1) NH(_4)-N was added to a batch culture. Fe-deficient cultures had lower nitrogenase activity and N content than Fe-sufficient cultures. Fe- deficiency led to the development of a series of new heterocysts apical to the basal ones. Addition of Fe to Fe-deficient cultures led to a marked increase in nitrogenase activity and loss of the degenerated basal heterocysts. The alga was capable of using a number of organic P substrates as the sole source of phosphorus and showed both cell-bound phosphomono- and phosphodiesterase activities. In batch culture, phosphatase activity was detected when cellular P content dropped to 0.98%. A brief study on the influence of the environmental factors on cell-bound phosphatase activities of the alga has been included. A brief comparison in nitrogenase activity of a UK field Rivularia population and bacterised laboratory isolate Rivularia D403 was made and probable behaviour of algae in DWR is discussed.

This thesis tests the hypothesis that variation in water supply, nutrient availability and irradiance determined variation in tree growth along local and regional gradients of resource availability, and over time, in Ghanaian forests. Regional variation in soil water availability determined seasonal patterns of diameter change of Celtis mildbraedii and Strombosia glaucescens in semi-deciduous and evergreen forest, over two years. However, in a semi-deciduous forest, annualized diameter increment of Celtis mildbraedii was higher in summit and slope, compared to valley, positions after two years, even though trees in valley positions experienced a shorter effective dry season. Growth was also greater in the semi-deciduous than the evergreen forest in the second year of the study. These patterns suggest that concentrations of N in soil over topographic gradients, and concentrations of available P and the base cations over regional scales, may be important determinants of growth. Dry season stem shrinkage in semi-deciduous forest can comprise up to 0.5% of tree diameter, and varies between years. Re-enumeration of forest plots in seasonal climates should be carried out over whole year intervals, during the wet season, to minimise bias derived from variation in tree water status. In a semi-deciduous forest, no relationship was found between topography and six year growth rates of two common species or of six functional types defined on the basis of regeneration strategy and regional distribution pattern. However, within this forest, and in a comparison within five different forests across the regional gradient of rainfall and soil fertility, pioneer species with distributions biased towards drier forests had significantly higher growth rates than pioneer species associated with wetter forests. Variation in growth of dry forest pioneer species explained more than half the total variation in stand-level growth rates, demonstrating that it is the presence of abundant, potentially large, fast growing pioneer species in more seasonal forest types that generate regional scale variation in forest growth. These results indicate that the environmental variables found to determine growth are dependent on the scale of the study and the magnitude of the gradient in resources being compared. Variation in soil fertility over regional rainfall gradients in tropical forests has a significant impact on variation in tree growth, within and between species, and at the stand-level.

Condensed tannins or proanthocyanidins (CTs) are polymeric flavonoids and common plant secondary metabolites. They are defined by their protein binding capacity, and anti-oxidant and metal chelating properties. Known functions of CTs include anti-herbivore and anti-microbial defenses. Chemical ecology studies, especially on CTs, have focussed almost exclusively on foliar chemistry and above-ground ecological interactions. However, CT concentrations in roots can match and far exceed those found in leaves, particularly in woody plant species. This suggests that CTs are also likely to have important ecological and physiological roles below-ground. A review of the literature suggests three potential roles of root CTs: 1) defense against soil pathogens and root herbivores; 2) facilitating adaptation to toxic soils through heavy metal chelation, and; 3) facilitating or modulating nutrient uptake through the binding of nutrient cations. In this thesis the relationship between root CTs and nutrient uptake will be analysed in P. tremula x alba. Localization of CTs was determined through both quantitative and histochemical techniques. Quantitation of CTs with the 1-butanol:HCl assay clearly showed that CT concentration was higher in the white root zone compared to the brown root zone or cork zone. This is inconsistent with the term ‘condensed tannin zone’ that is commonly used to describe the macroscopic brown zone of the root between the white zone and the cork zone in Pinus. The tissue specific localization of CTs in roots was determined using the CT-specific stain, 4-dimethylaminocinnamaldehyde (4-DMACA), on embedded longitudinal and fresh cross sections. These stained sections showed that CTs were present in cells on the root surface, specifically accumulating in the root cap and epidermal cells. CTs were also sporadically present in the cortical cells of the young, white root zones. CT concentration declined as distance from the root tip increased. The pattern of CT distribution, as indicated by intensity of the staining, corresponded directly to the quantitative assay results. Growing poplars under low nitrogen availability stimulated higher root CT concentrations than when they were grown under high nitrogen availability, suggesting a link between nitrogen and CTs. Since CTs are known to bind cations in vivo, I hypothesized that root CTs may modulate or facilitate nutrient uptake by binding positively charged nutrient ions. The Microelectrode Ion Flux Measurement (MIFE) technique was used to analyse specific fluxes of NH4+, NO3- and Ca2+ at specific root locations in poplar roots, and test for spatial correlation with CT localization. This technique was also used to compare the NH4+, NO3- and Ca2+ fluxes in transgenic high-CT and wild-type lines of Populus tremula x alba to test the impact of CTs on nutrient uptake directly. No correlation was found between fluxes of NH4+, NO3- or Ca2+ and CT distribution. The data indicate that root CTs do not influence nutrient uptake in Populus. This study provides data regarding the pattern of CT distribution as well as fundamental information on nutrient uptake in P. tremula x alba roots. It provides new knowledge that will be used to stimulate investigations on other potential roles of root CTs. / Graduate