Cover crops (CC) are planted in between cash crops to improve soil quality and to supply nitrogen (N) to cash crops through biological N fixation or soil N scavenging. Most producers use single species CC, in part because potential benefits of using mixtures of three or more CC species are poorly understood. A three-year study was initiated at Painter, Virginia to observe effects of CC mixtures on a no-till (NT) corn (Zea mays), wheat (Triticum aestivum L.), and soybean (Glycine max) rotation to measure CC performance, N cycling, cash crop yield, and soil quality in a sandy, low organic matter soil. Twelve treatments were created with conventional tillage (CT), NT, no CC control, and monoculture or CC mixtures of 3 to 9 species. Corn was grown in year 3 in all 12 treatments and four N rates were applied (0, 56, 112 and 156 kg N ha-1). Cover crop biomass, N accumulation, CC C:N ratio, and corn and soybean yield were measured annually. Soil bulk density, compaction, infiltration rate, pH, electrical conductivity, soil respiration, earthworm counts, soil microbial respiration, and soil microbial biomass carbon (C) after three years of CC. Cover crop biomass production varied significantly each year (5633 kg ha-1 in year 1, 755 kg ha-1 in year 2, 5370 kg ha-1 in year 3) due to climate and agronomic parameters, but a CC mixture always produced the highest biomass at termination. Nitrogen accumulation was strongly correlated with biomass production (R2= 0.94) and followed the same trend due to all CC having C:N < 30:1. Corn and soybean yields in years 1 and 2 were not significantly different, but corn yield was significantly affected by treatment and N fertilizer rate in year 3. After 3 years, soil respiration, earthworm populations and soil microbial biomass C increased in CC compared to CT without CC. However, infiltration rate, bulk density, microbial respiration, pH did not improve or declined compared to CT. In conclusion, adding CC mixtures to crop rotations shows promise for producing high CC biomass, accumulating N, and increasing crop yields, while improving some soil quality parameters on sandy low organic matter soils. / Doctor of Philosophy / Cover crop (CC) are planted in between cash crops to protect the soil from erosion, improve soil quality, and supply N to next cash crop through biological N fixation or soil N scavenging. Traditionally, CC were single species, but new CC methodologies utilize mixtures of three or more species planted together to protect soils as well as produce high biomass to suppress weeds, conserve soil moisture, and improve soil quality. A long-term study was initiated in fall 2014 in Painter, VA to observe CC mixture effects on no-till (NT) corn (Zea mays), wheat (Triticum aestivum L.), and soybean (Glycine max) rotations on CC performance, N cycling, cash crop yield, and soil quality of a sandy, low organic matter soil. Twelve treatments were created that compared NT rotations with CC monocultures, CC mixtures of 3-9 species, and without CC. In the third year corn was grown in all 12 rotations and four N rates were applied (0, 56, 112 and 156 kg N ha-1). To evaluate CC mixture performance in rotations, CC biomass, CC N accumulation and corn and soybean yield was measured over three years. To evaluate changes in soil quality, nine soil physical, chemical and biological soil properties were measured after three years of NT and CC. Biomass production varied significantly each experimental year (5633 kg ha-1 in year 1, 755 kg ha-1 in year 2, 5370 kg ha-1 in year 3) due to climate and agronomic differences, but CC mixtures were the highest biomass producing CC each spring and accumulated the highest amount of N. Cover crop mixtures had equal corn and soybean yield as CC monocultures. In year 3 corn yield and was greater in treatments with CC than in treatments without CC and was greater in legume dominated monocultures and mixtures than majority grass CC mixtures and monocultures. After 3 years of CC and NT, some soil quality parameters improved. Indicators of soil biology (soil respiration, earthworm populations, and soil microbial biomass C) increased in CC treatments. However, some soil physical and chemical properties (infiltration rate, bulk density, pH and EC) did not improve. In conclusion, adding CC mixtures to crop rotations shows promise for producing high CC biomass, accumulating N, and increasing crop yields, while also improving some soil quality parameters that are important for agricultural systems.

A field study was conducted in 2022 and 2023 at two different locations in Mississippi (MS) implementing a split-plot design. Nitrogen (N) rates as the main plot including 0 (control), 90, 180, 269 kg N ha-1 at Starkville and 224 kg N ha-1 at Stoneville. The subplot was seven treatments, including a no biostimulant (check) and six commercially available microbial biostimulants (Source Corn®, Envita®, iNvigorate®, Blue N®, Micro AZTM, and Bio level phosN®) applied either as foliar at V4-V5 growth stages or in-furrow at planting. Only N rates positively affected grain yield and nitrogen use efficiency at all site years. The agronomic optimum N rate (AONR) differed across all site years, ranging from 202, 128, and 166 kg N ha-1 at Starkville 2023 and Stoneville 2022 and 2023. In summary, microbial biostimulants within this study showed minimal to no effect on corn grain yield and all other tested parameters.

Nitrogen recovery and contribution to production agricultural systems are critical services provided by cover crops investigated in this study. Research was conducted to evaluate the effect of simulated residual N (SRN) on N recovery in various winter cover crop systems (CCS) and subsequent effects on corn N uptake. Biomass, C and N measurements, 15N recovery, and sources of N acquisition were quantified among CCS. Subsequently, CCS and SRN effects on corn productivity and N status were quantified. Grass-included CCS had the greatest N scavenging ability by CCS termination, though they had negative or neutral effects on corn N acquisition. Brassicas-included CCS were prolific early season N scavengers, though winterkill may have negated this effect. Legumes-included CCS generally accumulated large quantities of N and had narrow C:N ratios, positively affecting corn N acquisition. This study highlights the importance of context-specific CCS selection for N conservation.

Master of Science / Department of Agronomy / P.V. Vara Prasad / Grain sorghum [Sorghum bicolor (L.) Moench] is an important crop in the semi-arid regions of Africa, Asia and United States. Productivity of grain sorghum is limited by soil fertility, especially nitrogen (N). Sorghum genotypes are known to vary in their response to nitrogen, however, the information on nitrogen use efficiency (NUE) is limited. The objectives of this research were to (a) determine the response of sorghum genotypes (hybrids and inbred lines) to nitrogen fertilizer (b) quantify genotypic differences in NUE; and (c) determine physiological and morphological basis of NUE. Field experiments were conducted at three locations in Kansas (Hays, Ottawa and Manhattan) during 2010 and 2011. Six hybrids and six inbred lines of grain sorghum were grown with 0, 45 and 90 kg N ha-1.The experimental design was a split-plot design with N regimes as main plots and genotypes as sub-plot, with four replications. Planting was done in May and June across all the locations, and nitrogen fertilizer (Urea, 46% N) was applied at emergence. Data on N concentration in the leaves, stems and grain were determined. NUE and components of N use were computed for Ottawa and Manhattan as follows: Nitrogen use efficiency (NUE): Grain weight / N supplied; Nitrogen utilization efficiency: Grain weight / N total in plant; Nitrogen uptake efficiency: N total in plant / N supplied; Percent fertilizer recovery = [uptake (fertilized plot) – N uptake (un- fertilized plot)] / [ N applied ] x 100; and Nitrogen harvest index (NHI) = Grain N / N total in plant. Where N supplied = Rate of N fertilizer applied + soil N supplied. Growth and yield data were collected at all locations. There were significant effects of genotypes (P < 0.05) and nitrogen (P < 0.05) on biomass and grain yield across all locations. Performance of hybrids was generally superior to the inbred lines of all traits. Sorghum hybrids 26506 and 99480 produced maximum grain yield across all locations. While inbred lines B35 and SC35 had the lowest grain yield. Maximum biomass and grain yield was obtained at 90 kg N ha-1, followed 45 kg N ha-1, and lowest in 0 N kg ha-1. There were significant differences among genotypes for all NUE traits at Ottawa and Manhattan. Across genotypes, total NUE ranged from 17.2 to 42.6 kg kg-1, utilization efficiency from 24.3 to 60.2 kg kg-1, N uptake efficiency ranged from 56.1 to 82.5%, recovery from 2 to 52%, and NHI from 43.6 to 81.3%. Among the genotypes, 99480 and 26506 both known to be post–flowering drought tolerance were high in NUE and component of N use. While genotypes B35 and SC35 were the lowest in NUE and components of N use. Overall, our data suggest that there were significant differences for NUE traits in sorghum hybrids and inbred lines. There are opportunities to breed for higher NUE in grain sorghum.

Call number: LD2668 .T4 1933 B72

LD2668 .T4 1947 C7 / Master of Science

Call number: LD2668 .T4 1955 K64 / Master of Science

Co(NO)(NO₂)₂L₂ complexes (L = PPh₃, PMePh₂, PMe₂Ph, PMe₃, PEt₃, PEt₂Ph, PEtPh₂, PPrPh₂, PBu₃ and 1/2DPPPr) were prepared from the reactions of Co(NO)X₂L₂ (X = Cl, Br) with sodium nitrite in methanol freshly distilled from magnesium methoxide. The complexes were characterized by elemental analysis, 15-N labeling, infrared and NMR spectroscopy. The crystal structure of Co(NO)(NO₂)₂(PMePh₂)₂ was determined by X-ray diffraction. The cobalt atom has tetragonal pyramidal geometry. The nitrosyl group in the axial position is strongly bent. The NO₂ ligands have two different ligating geometries: one is bound to cobalt through the nitrogen atom and the other is bidentate forming an asymmetric four membered ring. The phosphine ligands are equivalent and trans to each other. Multinuclear NMR spectroscopy (¹H, ³¹P, ¹⁵N and ¹⁴N) was used to determine the solution structure of Co(NO)(NO₂ )₂L₂ complexes, to study mono and bisnitrosyls of cobalt, to establish some correlations between NMR parameters and structural characteristics of these complexes and to follow their reactions in solution. Reactions of Co(NO)(NO₂)₂L₂ with CO, NO and RCOX were observed to produce Co(NO)₂XL complexes. Since the structure may be indicative of electronic requirements at the metal center as well as the reactivity of the compounds, The crystal structures of Co(NO)₂Cl(PPh₃) and Co(NO)₂(ONO)(PPh₃) were also determined. In these complexes the cobalt atoms have pseudotetrahedral geometry. The CoNO angles are in the range considered to be linear. They are geniculated in an "atracto" conformation. Co(NO)(NO₂)₂L₂ and Co(NO)₂(ONO)L complexes react with oxygen in the solid state or in solution to form Co(NO₃)₂(OL)₂ complexes. When the reactions with O₂ were carried out in the presence of an excess of olefins, the formation of nitrates is inhibited Co(NO₂)₂(OL)₂ and olefin oxides are formed instead. The crystal structures of Co(NO₃)₂(OPMePh₂)₂ and Co(NO₂)₂(OPMePh₂)₂ were determined by X-ray diffraction. In these complexes, the NO₃ and NO₂ groups are bidentate. They are arranged in a cis configuration around the cobalt atom.

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Dissertation (PhD)--University of Stellenbosch, 2002. / ENGLISH ABSTRACT: Saccharomyces cerevisiae uses the nitrogenous compounds in its environment selectively. The basis of this phenomenon is the transcriptional regulation of genes whose products are required for nitrogen catabolism. A rich nitrogen source represses the expression of genes required for the degradation of poor nitrogen sources via the action of the target of rapamyein (TOR) signaling cascade. If only a poor nitrogen source is available, these genes are derepressed. This process is known as nitrogen catabolite repression (NCR) or nitrogen regulation. The DALI and DAL4 genes of S. cerevisiae are transcribed divergently from the 829 bp intergenic region. The five known UASNTR elements (GATAI-5) were mutated in the full context of the intergenic promoter. All five elements are required for the transcriptional activation of DAL4. The two elements most proximal to DAL4 (GATA4 and GATA5) contributed the most and the one most distal (GATAI) contributed the least to its expression. In contrast, three of the five elements (GATA2-4) are required for DALI activation. In addition, analyses revealed that no single element is shared equally between these two genes. Predictions as to the function of known nitrogen-regulating elements based on their sequence and location proved to be inaccurate in some cases. Mutation analyses of the three UISALL elements present in the intergenic promoter region revealed that UIS8, which does not share a high degree of homology with the consensus UISALL sequence, is required the most for transcriptional induction of both DALI and DAL4. Also, UIS7, which shares the most similarity with the UISALL consensus sequence, has the phenotype of a repressor-like element when mutated. These observations therefore portray the opposite phenotypes of what was expected. We identified a regulator, Vid30p, which is required for the transcriptional response of S. cerevisiae in low ammonia conditions. Genetic analyses of the vid30/j, mutant indicate that Vid30p functions by regulating the expression of genes required for the production and degradation of glutamate. The transcription of VID30 is NCR-sensitive, highly induced by low concentrations of ammonia, and rapamycin-sensitive. In addition, the vid30/j, mutant is hypersensitive to rapamycin, indicating that this protein is, directly or indirectly, controlled by the TOR signaling pathway. / AFRIKAANSE OPSOMMING: Saccharomyces cerevisiae het die vermoeë om stikstofbronne vanuit die omgewing selektief te benut. Die basis van hierdie verskynsel is die transkripsionele regulering van gene wat vir proteïene kodeer wat stikstof katabolisme bemiddel. 'n Goeie stikstofbron onderdruk die transkripsie van gene wat met die degradering van swak stikstofbronne gemoeid is. Hierdie onderdrukking word deur die teiken-van-rapamisien (TVR)-seintransduksiepad bewerkstellig. Wanneer slegs 'n swak stikstofbron beskikbaar is, word hierdie gene geaktiveer. Hierdie verskynsel staan as stikstofkatabolietonderdrukking (SKR) of stikstofregulering bekend. Die DALI- en DAL4-gene van S. cerevisiae word divergent vanaf 'n 829 bp intergeniese area getranskribeer. Vyf UASNTR-elemente (GATAI-5) is in die volle konteks van die intergeniese promotor gemuteer. Al vyf elemente word vir DAL4 transkripsionele aktivering benodig. Die twee elemente mees proksimaal tot DAL4 (GATA4 en GATA5) lewer die grootste bydrae tot DAL4-geenuitdrukking, terwyl die mees distale element (GATAI) die kleinste bydrae lewer. In teenstelling hiermee lewer slegs drie van die vyf elemente (GATA2-4) 'n noemenswaardige bydrae tot DALI se uitdrukking. Nie een van die vyf elemente lewer 'n gelykwaardige bydrae tot die uitdrukking van DALI en DAL4 nie. Voorspellings betreffende die bydrae van die onderskeie UASNTR-elemente tot die uitdrukking van die DALI- en DAL4-gene, gebaseer op die sekwens en die posisie van die element in die promotor, was meestal onakkuraat. Die drie U/SALL-elemente in die intergeniese area is gemuteer en toon dat U/S8, wat nie 'n groot mate van homologie met die U/SALL konsensus sekwens deel nie, die mees kritiese element vir transkripsionele induksie van beide DALI en DAL4 is. UIS7, wat 'n hoër mate van homologie met die UISALL konsensus sekwens deel, toon die fenotipe van 'n onderdrukkingselement wanner dit gemuteer word. Hierdie waarnemings is dus die teenoorgestelde van wat verwag is. Ons het 'n reguleerder, Vid30p, geïdentifiseer wat benodig word VIr die transkripsionele response van stikstofgereguleerde gene in lae konsentrasie ammonium. Genetiese analises van die vid3011 mutant toon dat Vid30p funksioneer deur die transkripsie van gene gemoeid met die vorming en degradering van glutamaat te reguleer. Die transkripsie van V/D30 is SKO-sensitief, word sterk deur lae konsentrasies ammonium geïnduseer, en is rapamisien-sensitief. Die vid30t!. mutant is ook hipersensitief vir rapamisien, wat aandui dat Vid30p, direk of indirek, deur die TVR-seintransduksiepad gereguleer word.