Viljelusviisi mõju mulla viljakusele ja talinisu taina kvaliteedile

A Thesis for applying for the degree of Doctor of Philosophy in Agriculture.Väitekiri filosoofiadoktori kraadi taotlemiseks põllumajanduse erialal.The long - term effect of organic and mineral nitrogen fertilizers on soil fertility in five - field crop rotation and on the quality of winter wheat grain yield and dough was studied in the doctoral thesis. The aim was to find out the long-term effect of organic and conventional cropping on total yield, soil fertility (phosphorus and potassium content, pH) and the combined effect of different cropping systems and year on the size distribution of starch granules, the yield of whole grain and fine flour, the interaction of gluten-starch on the rheological properties of wheat dough. The total yield of the five-field crop rotation was on average 25% higher than in organic farming due to mineral fertilizers. During the 10-year experimental period, the soil P content of the conventional treatments did not change, while the K content decreased to 40 mg K per kg dry soil and the soil became more acidic. The use of winter crops and well-composted cattle manure did not maintain the basic levels of P and K in the soil, which is why it is important to monitor the nutrient balance, especially in organic farming, so that soil fertility does not decrease. The effect of the cropping system on the size of the starch grains was not significant, but it was affected by the weather conditions during the experimental years. Flour yield was affected by the size distribution of starch granules, while the increased proportion of smaller diameter granules significantly increased the yield of fine flour. The quality of the dough was affected by several factors, with the nitrogen fertilization regime having a significant effect. If the protein content is more than 13% and the glutenin-gliadin ratio is optimal, the dough has a longer stability time, a lower softening degree and a higher dough quality. The quality of the dough varied more in the organic treatments. The amount of 150 kg/ha of mineral N applied in two parts before flowering ensured stable plant growth and protein and gluten content in different years. Treatments fertilized with lower amounts of nitrogen and organic treatments were more vulnerable to changing weather conditions.Doktoritöös uuriti orgaaniliste ja mineraalsete lämmastikväetiste pikaajalist mõju mulla viljakusele viieväljalises külvikorras ning talinisu terasaagi ja nisutaina kvaliteedile. Eesmärk oli välja selgitada mahe- ja tavaviljeluse pikaajaline mõju külvikorra kogusaagile, mulla viljakusele (fosfori- ja kaaliumisisaldusele, pH) ning eri viljelusviiside ja aasta koosmõju tärklise graanulite suuruse jaotusele, täistera ja peenjahu saagile, gluteeni-tärklise koostoimele nisutaina reoloogilistele omadustele. Tulemustest selgus, et viieväljalise külvikorra kogusaak oli mineraalväetiste toimel keskmiselt 25% kõrgem kui maheviljeluses. Kümneaastase katseperioodi jooksul tavaviljeluse variantide mullas ei muutunud taimele kättesaadava P sisaldus, samas K sisaldus vähenes kuni 40 mg K kg kuiva mulla kohta ning muld muutus happelisemaks. Talivahekultuuride ja hästi komposteerunud veisesõnniku kasutamine ei säilitanud mullas P ja K baastasemeid, mistõttu on oluline eriti maheviljeluses jälgida toitainete bilanssi, et mullaviljakus ei langeks. Viljelusviisi mõju tärkliseterade suurusele ei olnud märkimisväärne, küll aga mõjutasid seda usutaval määral ilmastikutingimused katseaastatel. Jahu saagikust mõjutas tärklise graanulite suuruse jaotus, samas kui väiksema läbimõõduga graanulite suurenenud osakaal suurendas oluliselt peene jahu saagikust. Taina kvaliteeti mõjutasid mitmed tegurid, kusjuures lämmastiku väetamise režiimil oli määrav mõju. Kui proteiinisisaldus on üle 13% ning gluteniini-gliadiini suhe on optimaalne, siis on taina stabiilsusaeg on pikem, pehmenemise tase madalam ja taina kvaliteet kõrgem. Taina kvaliteet varieerus enam mahevariantides. Mineraalse lämmastiku 150 kg/ha kogus, mida anti kahes jaos enne õitsemist, tagas taimede stabiilse kasvu ning valgu- ja gluteenisisalduse erinevatel aastatel. Väiksemate lämmastiku kogustega väetatud variandid ning mahevariandid olid muutuvate ilmastikutingimuste suhtes tundlikumad.Publication of this thesis is supported by the Estonian University of Life Sciences

How Do Galaxies Get Their Gas?

We examine the temperature history of gas accreted by forming galaxies in SPH simulations. About half the gas shock heats to roughly the virial temperature of the galaxy potential well before cooling, condensing, and forming stars, but the other half radiates its acquired gravitational energy at much lower temperatures, typically T<10^5 K, and the histogram of maximum gas temperatures is clearly bimodal. The "cold mode" of gas accretion dominates for low mass galaxies (M_baryon < 10^{10.3}Msun or M_halo < 10^{11.4}Msun), while the conventional "hot mode" dominates the growth of high mass systems. Cold accretion is often directed along filaments, allowing galaxies to efficiently draw gas from large distances, while hot accretion is quasi-spherical. The galaxy and halo mass dependence leads to redshift and environment dependence of cold and hot accretion rates, with cold mode dominating at high redshift and in low density regions today, and hot mode dominating in group and cluster environments at low redshift. Star formation rates closely track accretion rates, and we discuss the physics behind the observed environment and redshift dependence of galactic scale star formation. If we allowed hot accretion to be suppressed by conduction or AGN feedback, then the simulation predictions would change in interesting ways, perhaps resolving conflicts with the colors of ellipticals and the cutoff of the galaxy luminosity function. The transition between cold and hot accretion at M_h ~ 10^{11.4}Msun is similar to that found by Birnboim & Dekel (2003) using 1-d simulations and analytic arguments. The corresponding baryonic mass is tantalizingly close to the scale at which Kauffmann et al. (2003) find a marked shift in galaxy properties. We speculate on connections between these theoretical and observational transitions.Comment: 1 figure added, Appendix discussing SAMs added, some text changes. Matches the version accepted by MNRAS. 31 pages (MNRAS style), 21 figures,For high resolution version of the paper (highly recommended) follow http://www.astro.umass.edu/~keres/paper/ms2.ps.g

Moving mesh cosmology: tracing cosmological gas accretion

We investigate the nature of gas accretion onto haloes and galaxies at z=2 using cosmological hydrodynamic simulations run with the moving mesh code AREPO. Implementing a Monte Carlo tracer particle scheme to determine the origin and thermodynamic history of accreting gas, we make quantitative comparisons to an otherwise identical simulation run with the smoothed particle hydrodynamics (SPH) code GADGET-3. Contrasting these two numerical approaches, we find significant physical differences in the thermodynamic history of accreted gas in haloes above 10^10.5 solar masses. In agreement with previous work, GADGET simulations show a cold fraction near unity for galaxies forming in massive haloes, implying that only a small percentage of accreted gas heats to an appreciable fraction of the virial temperature during accretion. The same galaxies in AREPO show a much lower cold fraction, <20% in haloes above 10^11 solar masses. This results from a hot gas accretion rate which, at this same halo mass, is an order of magnitude larger than with GADGET, while the cold accretion rate is also lower. These discrepancies increase for more massive systems, and we explain both as due to numerical inaccuracies in the standard formulation of SPH. We also observe that the relatively sharp transition from cold to hot mode dominated accretion, at a halo mass of ~10^11, is a consequence of comparing past gas temperatures to a constant threshold value independent of virial temperature. Examining the spatial distribution of accreting gas, we find that gas filaments in GADGET tend to remain collimated and flow coherently to small radii, or artificially fragment and form a large number of purely numerical "blobs". Similar gas streams in AREPO show increased heating and disruption at 0.25-0.5 virial radii and contribute to the hot gas accretion rate in a manner distinct from classical cooling flows.Comment: 21 pages, 12 figures. MNRAS accepted (in press). High-resolution images can be found at http://www.cfa.harvard.edu/itc/research/movingmeshcosmology

The formation of massive, quiescent galaxies at cosmic noon

The cosmic noon (z~1.5-3) marked a period of vigorous star formation for most galaxies. However, about a third of the more massive galaxies at those times were quiescent in the sense that their observed stellar populations are inconsistent with rapid star formation. The reduced star formation activity is often attributed to gaseous outflows driven by feedback from supermassive black holes, but the impact of black hole feedback on galaxies in the young Universe is not yet definitively established. We analyze the origin of quiescent galaxies with the help of ultra-high resolution, cosmological simulations that include feedback from stars but do not model the uncertain consequences of black hole feedback. We show that dark matter halos with specific accretion rates below ~0.25-0.4 per Gyr preferentially host galaxies with reduced star formation rates and red broad-band colors. The fraction of such halos in large dark matter only simulations matches the observed fraction of massive quiescent galaxies (~10^10-10^11 Msun). This strongly suggests that halo accretion rate is the key parameter determining which massive galaxies at z~1.5-3 become quiescent. Empirical models that connect galaxy and halo evolution, such as halo occupation distribution or abundance matching models, assume a tight link between galaxy properties and the masses of their parent halos. These models will benefit from adding the specific accretion rate of halos as a second model parameter.Comment: 5 pages, 5 figures, to appear in MNRAS Letter

Galactic r-process enrichment by neutron star mergers in cosmological simulations of a Milky Way-mass galaxy

We quantify the stellar abundances of neutron-rich r-process nuclei in cosmological zoom-in simulations of a Milky Way-mass galaxy from the Feedback In Realistic Environments project. The galaxy is enriched with r-process elements by binary neutron star (NS) mergers and with iron and other metals by supernovae. These calculations include key hydrodynamic mixing processes not present in standard semi-analytic chemical evolution models, such as galactic winds and hydrodynamic flows associated with structure formation. We explore a range of models for the rate and delay time of NS mergers, intended to roughly bracket the wide range of models consistent with current observational constraints. We show that NS mergers can produce [r-process/Fe] abundance ratios and scatter that appear reasonably consistent with observational constraints. At low metallicity, [Fe/H]<-2, we predict there is a wide range of stellar r-process abundance ratios, with both supersolar and subsolar abundances. Low-metallicity stars or stars that are outliers in their r-process abundance ratios are, on average, formed at high redshift and located at large galactocentric radius. Because NS mergers are rare, our results are not fully converged with respect to resolution, particularly at low metallicity. However, the uncertain rate and delay time distribution of NS mergers introduces an uncertainty in the r-process abundances comparable to that due to finite numerical resolution. Overall, our results are consistent with NS mergers being the source of most of the r-process nuclei in the Universe.Comment: Accepted for publication in MNRAS, 10 pages and 4 figures. Revised version: minor change

Reconciling dwarf galaxies with LCDM cosmology: Simulating a realistic population of satellites around a Milky Way-mass galaxy

Low-mass "dwarf" galaxies represent the most significant challenges to the cold dark matter (CDM) model of cosmological structure formation. Because these faint galaxies are (best) observed within the Local Group (LG) of the Milky Way (MW) and Andromeda (M31), understanding their formation in such an environment is critical. We present first results from the Latte Project: the Milky Way on FIRE (Feedback in Realistic Environments). This simulation models the formation of a MW-mass galaxy to z = 0 within LCDM cosmology, including dark matter, gas, and stars at unprecedented resolution: baryon particle mass of 7070 Msun with gas kernel/softening that adapts down to 1 pc (with a median of 25 - 60 pc at z = 0). Latte was simulated using the GIZMO code with a mesh-free method for accurate hydrodynamics and the FIRE-2 model for star formation and explicit feedback within a multi-phase interstellar medium. For the first time, Latte self-consistently resolves the spatial scales corresponding to half-light radii of dwarf galaxies that form around a MW-mass host down to Mstar > 10^5 Msun. Latte's population of dwarf galaxies agrees with the LG across a broad range of properties: (1) distributions of stellar masses and stellar velocity dispersions (dynamical masses), including their joint relation; (2) the mass-metallicity relation; and (3) a diverse range of star-formation histories, including their mass dependence. Thus, Latte produces a realistic population of dwarf galaxies at Mstar > 10^5 Msun that does not suffer from the "missing satellites" or "too big to fail" problems of small-scale structure formation. We conclude that baryonic physics can reconcile observed dwarf galaxies with standard LCDM cosmology.Comment: 7 pages, 5 figures. Accepted for publication in ApJ Letters. Several updates, including: (1) fixed a bug in halo finder, now identifies 13 satellite galaxies and more subhalos in the baryonic simulation; (2) fixed a minor bug in the feedback coupling and reran the simulation, resulting in a somewhat lower-mass host galaxy; (3) Fig 2 now shows stellar velocity dispersion profiles of satellite

Giant clumps in the FIRE simulations: a case study of a massive high-redshift galaxy

The morphology of massive star-forming galaxies at high redshift is often dominated by giant clumps of mass ~10^8-10^9 Msun and size ~100-1000 pc. Previous studies have proposed that giant clumps might have an important role in the evolution of their host galaxy, particularly in building the central bulge. However, this depends on whether clumps live long enough to migrate from their original location in the disc or whether they get disrupted by their own stellar feedback before reaching the centre of the galaxy. We use cosmological hydrodynamical simulations from the FIRE (Feedback in Realistic Environments) project that implement explicit treatments of stellar feedback and ISM physics to study the properties of these clumps. We follow the evolution of giant clumps in a massive (stellar mass ~10^10.8 Msun at z=1), discy, gas-rich galaxy from redshift z>2 to z=1. Even though the clumpy phase of this galaxy lasts over a gigayear, individual gas clumps are short-lived, with mean lifetime of massive clumps of ~20 Myr. During that time, they turn between 0.1% and 20% of their gas into stars before being disrupted, similar to local GMCs. Clumps with M>10^7 Msun account for ~20% of the total star formation in the galaxy during the clumpy phase, producing ~10^10 Msun of stars. We do not find evidence for net inward migration of clumps within the galaxy. The number of giant clumps and their mass decrease at lower redshifts, following the decrease in the overall gas fraction and star-formation rate.Comment: 20 pages, 19 figures; revised version, accepted for publication in MNRA