Inaug.-diss.--Jena. / Lebenslauf. "Literaturverzeichnis": p. 157-158.

Thesis (M.S.)--Montana State University--Bozeman, 2007. / Typescript. Chairperson, Graduate Committee: Fabian D. Menalled. Includes bibliographical references.

Crop rotation is a key strategy of sustainable agriculture in the Canadian Prairie. Improving crop productivity and yield stability in pulses-based cropping systems with better soil biology is the ultimate goal of this research. Firstly, my studies provide information on the effect of pulses on the biodiversity of soil fungi: arbuscular mycorrhizal fungi (AM) and non-AM fungi, associated with the main pulse species grown in the Canadian Prairie (field pea, lentil, and chickpea), and their influence on wheat-based cropping systems. Secondly, the optimum 4-yr crop rotation for wheat production was determined, based on the relationship among fungal communities associated to the different crops and the yield and quality of these crops. My research included two experiments. First, in a field experiment replicated in time and site, the effect of previous pulse crops on wheat root-associated microbial communities and crop performance was assessed in four 2-yr rotation systems. Second, a 4-yr field experiment evaluated the relative influence of eight different crop rotations on root-associated microbial communities and on wheat productivity in the last year of the rotations. A greenhouse assay was conducted to evaluate, under controlled conditions, the influence of the microbial communities selected by these previous field crop rotations on wheat performance, using soil from the field as inoculant. The response of root-associated microbial communities was characterized using next generation sequencing technologies, phospholipid fatty acid markers, microscopic observation of roots and soil dehydrogenase assay. Plant response was evaluated based on crop density, biomass, yield and tissue nutrient content. My studies showed that community composition of AM and non-AM fungal communities in the roots of wheat were largely influenced by host plant identity and environmental conditions. The structure of the overall fungal community in wheat roots was not affected by the previous crops. The soil microbial legacies of previous crops were different from the fungal communities found in the roots of the following wheat, suggesting that wheat, as a host plant, selects and associates with a specific fungal community. Seasonal variations in soil moisture, temperature, pH, and nutrient cycling between sampling times have a great influence on soil microbes and could also be influencing these effects. The 2-yr crop rotation experiment revealed that wheat after a pulse crop had higher plant density and produced more seed biomass and total yield. The 4-yr crop rotation studies revealed that, in the field, diversified rotations including pea or lentil in alternate years, largely contributed to wheat performance. However, rotations including chickpea contributed little to the rotation benefits, suggesting that a careful selection of plant species is essential to improve the performance of the agroecosystem. Contrary to the field results’ findings, under greenhouse conditions, rotations that included chickpea before wheat contributed the best to wheat productivity, suggesting that in the field, factors other than the microbial community selected by chickpea were responsible for the poor performance of chickpea-wheat rotations in the field. Soil bacterial and fungal biomasses were positively correlated with wheat yield in the field experiments, which suggests that an abundant and diversified microbial community positively influences wheat productivity. Also, possible antagonistic and synergistic interactions between different AM species and root pathogens could be inferred. These results suggest that many AM fungi can potentially contribute to combat pathogens and enhance plant performance, whereas other might produce detrimental effects on the plants. Overall my studies revealed that host plant identity and environmental conditions influence the fungal community structure and dynamics. The frequency and sequence of crops in the rotations strongly influences productivity in wheat based agroecosystems. Lentil and pea alternating with wheat largely contribute to wheat performance. Thus, the productivity of wheat can be improved by selecting and including the plant species most beneficial to the rotation in order to increase soil available water and N, while promoting beneficial microbial associations and reducing disease incidence.

No description available.

Every farmer has realized the dangers which follow from growing the same crop too frequently on the same land. Out of his experience and observations there has grown up the idea that one crop poisons another of the same kind, and that if he desires success he must do something to restore and maintain the fertility of the soil — and that crop rotation is one of the best means of accomplishing this result. To ascertain what really lies at the basis of this idea — whether a plant excretes poison? and if so what is their nature and what relation do these bear to soil fertility -- has attracted the attention of both practical farmers and scientific investigators from the very earliest times. But it is only during the last few years that any advance has been made in the study of these plant poisons, which promises to throw some light upon problems of soil conditions and ecological relations.

No description available.

Field studies were conducted to evaluate the effect of crop rotation on annual bluegrass plant population dynamics, seed rain, and seed bank in 1996 and 1997 at two sites. Growth-chamber studies were conducted to determine the influence of the mother plant environment on annual bluegrass germination. The change in population, seed rain, seed in seed bank and germination behavior of annual bluegrass at Site 1 was different from those at Site 2. The highest population of annual bluegrass was observed in the meadowfoam-perennial ryegrass rotation and the lowest population was observed in the continuous perennial ryegrass and meadowfoam-spring wheat rotations at Site 1 in 1997, whereas continuous perennial ryegrass and winter wheat-perennial ryegrass rotations had the highest populations at Site 2 in 1997. Differences in the number of annual bluegrass seed in the seed bank occurred at both sites. The greatest reduction of annual bluegrass seed in the seed bank was observed over time in the meadowfoam-spring wheat rotation at both sites. At both sites, most of the seed was deposited on the surface to 0 to 2.5 cm soil depth and the number of seed decreased with soil depth. The mother plant environment and the date of seed maturity had an effect on annual bluegrass germination. At the seed collection date of 5/8/97, the annual bluegrass seed collected from the canopy of continuous perennial ryegrass and from the seedling perennial ryegrass following meadowfoam had the highest germination at 15/25 C at Site 1. Seed collected from continuous perennial ryegrass on 5/6/97 and 5/22/97 had the highest germination among all test temperatures regimes at Site 2. Seed collected from seedling perennial ryegrass following meadowfoam at the second collection date of 5/28/97 at Site 1 and 5/22/97 at Site 2 had the lowest germination at all temperature regimes except 5 C constant temperature. The 15/25 C was the best temperature regime for germination of annual bluegrass collected from any mother plant environment on any seed collection date at Site 1 and Site 2. / Graduation date: 1999

Thesis (MScAgric)--University of Stellenbosch, 2008. / Bibliography. Also available via the Internet.

Thesis (M.S.) in Plant, Soil and Environmental Sciences--University of Maine, 2003. / Includes vita. Includes bibliographical references (leaves 79-84).

Weens die unieke eiesoortigheid van die mens is sy behoeftes vanselfsprekend uiters divers. Wat vir die een persoon prioriteit is, mag vir sy buurman geensins belangrik wees nie. Dit is egter ook ’n gegewe, dat die mens heelwat gemeenskaplike ervarings, emosies en behoeftes deel. Een hiervan is die behoefte wat hy het om te weet dat die besluit wat hy gaan of wil neem die regte een binne die konteks van sy keuse mag wees. Die woord ‘behoefte’ kan waarskynlik in hierdie geval vervang word met die begrip ‘genade’. Sonder om 'n platvorm vir debat te skep, word die stelling gehandhaaf dat ‘genade’ slegs van die Skepper afkomstig is. Met hierdie stelling as agtergrond was dit 'n minder aangename ervaring om vir feitlik twintig jaar te moes toekyk hoe koringboere hul besluite, veral met betrekking tot die samestelling van wisselboustelsels, moes neem, klaarblyklik in totale gebrek aan die gawe van ‘genade’. Nodeloos om te sê, met gepaardgaande negatiewe gevolge. Die meer gemaklike verontskuldiging is om te redeneer dat ons Skepper relatief suinig is met die uitdeel van sy ‘genade’. Alvorens die begrip van Prediker 10:10 nog nie ten volle begryp is nie, kan so 'n stelling dalk makliker gemaak word. Hierdie gedeelte uit die Skrif sê in werklikheid die teenoorgestelde – dat God baie vrygewig is met Sy ‘genade’, maar dat die mens sy gesonde verstand moet gebruik om dit ten volle te benut. Die wens is dat hierdie studie, 'n deel sal uitmaak van die proses om die byl skerp te maak om sodoende die houtkap-proses effektief uit te voer.