<p>  </p> <p>The objectives of this dissertation included comparing the whole gut bacterial profiles of insecticide resistant and susceptible <em>B. germanica</em> and determining how these profiles, as well as the structure and function of the gut microbiome, change in the presence of an antibiotic. Additional goals were to investigate how antibiotic treatment impacts the toxicity of the bait insecticides fipronil, abamectin and indoxacarb, and to determine how gut bacteria, and specifically the enzymes originating within gut bacteria, metabolize and convert ingested indoxacarb into its toxic metabolite DCJW. Findings show that pre-treatment with the antimicrobial compound kanamycin (KAN) led to reductions in resistance levels for fipronil and abamectin, but also increased basal toxicity levels in both resistant and susceptible strains tested. 16S bacterial sequence surveys revealed that resistant and susceptible cockroach strains were more similar before KAN treatment than after, with a stronger dysbiosis effect in the resistant strain. For the insecticide indoxacarb, regardless of strain, roaches treated with kanamycin-infused water in feeding bioassays were more susceptible compared to the control treatment, but in vial (surface contact) bioassays, only susceptible cockroaches experienced a significant shift in mortality. When the frass of indoxacarb-fed cockroaches was analyzed, fewer molecules of the hydrolytic metabolite DCJW were produced with the introduction of an antibiotic (KAN). This result was further corroborated by esterase activity assays of whole homogenized cockroach guts. All results considered, these findings provide novel evidence of microbe-mediated pro-insecticide activation in the cockroach gut. Overall, the results of this dissertation reveal previously unknown relationships between gut microbiota and their insect hosts. These microbiome relationships exposed important cockroach strain differences which may extend to the host population level. Furthermore, this research has connected a change in enzyme activity in the gut microbiome with indoxacarb, a very important marketplace pro-insecticide.</p>

<p>Urea has been widely used as a crop fertilizer to increase crop yield. The low nutrient use efficiency (NUE) of urea, however, is a challenge. Coated fertilizers are considered a solution not only for enhancing the NUE but also for alleviating soil and water pollution. In this paper, the physical properties of coated fertilizers were analyzed, including their particle size distribution, fracture force, thermal behavior, envelope density, and apparent density (regular fertilizer: pure urea and the Anderson 12-6-6; slow release fertilizer: Osmocote 14-14-14, the Anderson 18-6-12; controlled release fertilizer: Environmentally smart nitrogen (ESN), Florikan 14-14-14, Everris 17-3-6). The granules’ closed and open pore number, pore volume, and total porosity were analyzed using X-ray micro-tomography (XRCT). The results demonstrated that pure urea and Florikan have a similar median particle size, around 4 mm, while ESN and Osmocote have a similar median particle size of around 3 mm. Finally, Everris, the Andersons 18-6-12, and the Andersons 12-6-6, have a similar median particle size of roughly 2.5 mm. The fracture pressure of ESN (4.58±0.98 MPa) and the NPK combination fertilizers (Florikan: 9.40±1.46 MPa and Osmocote: 8.94±2.09 MPa) were higher than pure urea. The envelope and apparent density of pure urea (envelope: 1.22±0.02 kg/m³ and apparent: 1.27±0.01 kg/m³) and ESN (envelope: 1.26±0.03 kg/m³ and apparent: 1.27±0.00 kg/m³) are similar, while all NPK fertilizers have a significantly higher density (envelope: 1.68–1.87 kg/m³ and apparent: 1.83–2.09 kg/m³). ESN had higher internal pore space and a higher total pore volume than pure urea, while NPK combination fertilizer showed lesser pores and significantly smaller pore volumes. The physical properties were also significantly different when comparing urea and NPK compound fertilizers, mainly because of the differences in their nutrient coatings and manufacturing methods. The coating of the urea increases the granule strength but does not alter the thermal properties; however, the overall porosity of the granules is influenced by the coating. In this thesis core, different binders were used to alter the internal structure of the urea granule to control the dissolution behavior and to make it a slow-release fertilizer. The layered agglomeration technique was used to manufacture the granules. The core of the granule was made by granulating technical urea powder in a drum granulator, with corn starch as the binder. A second layer of urea was added to the core by drum granulation in order to obtain a nutrient release pattern that matches with the crop demand. Corn starch, PEG 4000, and corn starch hydrogel were used as binders for the second layer. The density, thermal properties, strength, and internal porosity were measured to compare with market urea and coated slow-release fertilizer granules. All the dissolution rates of the double layer granules were slower than for market urea. Among these granule types, the dissolution rate curve of the granule with starch hydrogel in the second layer better matched the crop demand curve than those of the other two types of granules. Moreover, the strength of the double layer granules with hydrogel was the greatest of the three double layer granules. So, overall, the double layer granule manufactured with corn starch in the core and starch hydrogel in the second layer performed the best. Although the pattern of dissolution of the double layer granule was similar to the crop nitrate demand curve, a soil-based study is needed to verify the nitrate release characteristics.<br></p><ul> </ul>

<p>Control of weeds that have survived a postemergence (POST) herbicide often need to be controlled in order to prevent seed production and interference with crops. The most efficacious herbicides and timings used for respray applications has not been determined in many problematic weed species. Previous research has demonstrated that weeds clipped to simulate a failed herbicide application responded differently to herbicide applications to regrowth based on herbicide used and weed species. Other research is conflicting as to the optimum timing of an herbicide respray application with various herbicides. Gaining a better understanding of how to maximize respray herbicide performance will help growers and land managers to preserve crop yield and prevent weed seed production in the event of POST contact herbicide failure. The objectives of this research were to determine the optimum respray herbicide and timing combinations for control of four problematic weed species in the midwestern United States that have survived an application of either glufosinate or fomesafen: waterhemp<i> </i>[<i>Amaranthus tuberculatus</i> (Moq.) J. D. Sauer], Palmer amaranth (<i>Amaranthus palmeri</i> S. Watts), giant ragweed (<i>Ambrosia trifida</i> L.), and horseweed (<i>Erigeron canadensis</i> L). Through a series of field and greenhouse experiments we determined that respray herbicide, respray application timing, initial herbicide, and level of injury from the initial application influence efficacy of the respray herbicide in a species-specific manner. Waterhemp regrowth following a failed glufosinate application was controlled most effectively by applying glufosinate or fomesafen 7 to 11 days after initial treatment. When following fomesafen, applications of 2,4-D 3-7 days after initial treatment or glufosinate 7 to11 days after initial treatment were most effective. Control of Palmer amaranth regrowth following either initial herbicide is best achieved with respray applications of glufosinate, fomesafen, or 2,4-D applied no later than 7 days after initial treatment. The best strategy to control giant ragweed regrowth following a failed fomesafen applications is to apply 2,4-D, dicamba, fomesafen, or glufosinate at any timing between 3 and 11 days after initial treatment. Efficacy of the respray glufosinate application was maximized when applied 11 days after the initial application rather than 3 days after initial application. Horseweed regrowth was best controlled by 2,4-D, dicamba, or glufosinate applied at any timing between 3 and 11 days after the initial application. Where injury from the initial herbicide application is high, there were fewer differences among herbicide treatments and treatment timings. A greenhouse bioassay revealed that as waterhemp injury from an initial glufosinate application increases, control with a respray herbicide also increases. Therefore, complete control of weed regrowth is achieved more easily with increasing injury from the initial application. This research suggests that timing of herbicide respray applications is more urgent than previously thought, so scouting must be done within days of a contact herbicide application to ensure adequate control. </p>

An injection technique, in which undisturbed soil cores are labelled with ³²P to study dissolution of phosphate fertilisers in the soil, was evaluated in field and glasshouse trials. When ³²P was injected between 0-150 mm depths of the undisturbed soil columns and fertilisers applied at the surface, the amounts of fertiliser P dissolved, as measured by the increases in the exchangeable P pools, were overestimated. Three possible reasons were suggested: (i) the interaction between surface-applied fertiliser, ³²P injected through the whole soil column, and the vertical decline in root density, (ii) the decline of specific activity in the exchangeable P pool due to losses of ³²P to nonexchangeable P pools and continuous addition of P from fertiliser dissolution, and (iii) non-uniform distribution of ³²P vis-a-vis ³¹P phosphate. The injection technique may be employed to assess the effectiveness of phosphate fertilisers by introducing a concept, the fertiliser equivalent (FE). The FE is a measure of the amounts of soil exchangeable P that the fertilisers are equivalent to in supplying P to plants, when applied at the specific location. Soluble single superphosphate (SSP) applied at the surface of undisturbed grassland soil cores (Tekapo fine sandy loam), was much more effective than surface-applied unground North Carolina phosphate rock (NCPR) and 30% acidulated NCPR with phosphoric acid (NCPAPR) within the 56 day period of plant growth. An isotopic dilution method, based on tracer kinetic theory, was developed to study the rates of dissolution (F in) and retention (F out) of phosphate fertilisers in the soil in growth chamber experiments. The estimation of F in and F out required labelling of the soils with carrier-free ³²P and determination of the corresponding values of the specific activities of the exchangeable P pools, SA₁ and SA₂, and the sizes of the exchangeable P pools, Q₁ and Q₂, at times t₁ and t₂. Most of the phosphate in the monocalcium phosphate (MCP) solution entered the exchangeable P pool immediately after addition to the soils (Tekapo fine sandy loam and Craigieburn silt loam), and there was little further phosphate input. With increasing periods of incubation, the phosphate was quickly transformed to less rapidly exchangeable forms. In the soils treated with ground North Carolina phosphate rock (<150 µm, NCPR) or partially acidulated (30%) NCPR with phosphoric acid (NCPAPR), the initial exchangeable P pools were not as large as those in the soils treated with MCP, but were maintained at relatively stable concentrations for extended periods, due to the continuous dissolution of PR materials and to lower rates of pretention. An increase in P-retention caused a slight rise in the rate of PR dissolution, but also a rise in the rate of P-retention by the soil. The rate of dissolution was higher at a lower application rate in relative terms, but smaller in absolute terms. The trends in the changes of plant-available P in the soils, measured by the water extractable P, Bray I P and Olsen P, correspond to those predicted by the F in and F out values. The average rates of dissolution between 1-50 and 50-111 days estimated by the F in, however, were higher than those estimated by extractions with 0.5 M NaOH followed by 1 M HCl, and with 0.5 M BaCl₂/TEA. This is partly because the Fin values reflect a plant growth effect on PR dissolution. The relative agronomic effectiveness of NCPR and NCPAPR with respect to MCP was higher after 50 and 111 days of incubation than after 1 day. The F in values were included in all the two-variable models constructed by stepwise regression to describe the relationship between plant P uptake and soil measurements. The amounts of variation in plant P uptake accounted for by the regression model was significantly improved by including F in in the model. This indicates the importance of fertiliser dissolution rates in affecting soil P supply, when phosphate fertilisers differing in solubility are applied.

*‘Pasja’ (Brassica campestris x napus) and kale (Brassica oleracea var. acephala L.) were grown at Lincoln, Canterbury, New Zealand in 2008 with different levels of phosphorus (P) fertiliser. Banded or broadcast P fertiliser was applied at 0, 20, 40 and 60 kg P/ha at establishment. Total dry matter (DM) production, the proportion of the leaf and stem and leaf area development were measured over time and related to the biophysical environment. For ‘Pasja’, final DM increased with P rate from 3730 kg DM/ha to ~4900 kg DM/ha at 60 kg P/ha. For kale the increase was from 8710 kg DM/ha for the control to ~11000 kg DM/ha for all P treatments. The leaf to stem ratio declined from 22-31 at 17 days after emergence to 10.4 at the final harvest for ‘Pasja’, which meant the crop was effectively made up mainly of leaf (~90%). The ratio for kale declined from 2.7 at 24 days after emergence to 0.64 at the final harvest. The leaf to stem ratio for both species did not respond to either the method of application or rate of P. Seedling DM accumulation increased with applied P over the first 10 to 17 DAE for ‘Pasja’ and kale respectively. The crops went from shoot growth priority to root growth. The phyllochron of both species was unaffected by P application but responded linearly to the temperature above 0°C. For ‘Pasja’ the phyllochron was 60°Cd compared with 109°Cd for kale. As a consequence ‘Pasja’ developed its canopy and reached critical leaf area index (LAIcrit) earlier than kale. Leaf area index (LAI) for the control crops of both species was lower than for P fertiliser treatments with a maximum of 3.6 for ‘Pasja’ and 3.8 for kale. There was no difference in leaf area indices among the P fertiliser treatments for ‘Pasja’, while kale LAI differed with the rate of P application up to 40 kg P/ha. Total accumulated intercepted solar radiation (RIcum) was 8 and 11% greater for ‘Pasja’ and kale crops respectively when P was applied compared with the control. Thus, the difference in total dry matter yield due to P application was attributed to the difference in RIcum. Neither the method of application or rate of P applied affected the radiation use efficiency (RUE) of either crop. For ‘Pasja’ the RUE was 1.1 g DM/MJ PAR and for kale 1.33 g DM/MJ PAR. Based on this research, it was concluded that P application increased RIcum as a result of increased LAI. The difference in total DM yield was attributed to differences in RIcum. It is recommended that farmers growing ‘Pasja’ and kale under similar conditions to this experiment should apply 40 kg P/ha for ‘Pasja’ and band 20 kg P/ha for kale. *‘Pasja’ is considered both as a species and cultivar in this document as it marketed as such in New Zealand. Technically ‘Pasja’ is a leaf turnip.