Thesis (Ph. D.)--University of Missouri-Columbia, 1998. / Typescript. Vita. Includes bibliographical references. Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 1998. / Typescript. Vita. Includes bibliographical references. Also available on the Internet.

Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1993. / Vita. Abstract. Includes bibliographical references (leaves 27-32). Also available via the Internet.

Thesis (Ph.D.) - University of Queensland, 2003. / Includes bibliographical references.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1981. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references (leaves 87-95).

Thesis (M.S.) University of Missouri-Columbia, 2006. / The entire dissertation/thesis text is included in the research.pdf file; the official abstract appears in the short.pdf file (which also appears in the research.pdf); a non-technical general description, or public abstract, appears in the public.pdf file. Title from title screen of research.pdf file (viewed on August 27, 2007) Includes bibliographical references.

Master of Science / Department of Biological & Agricultural Engineering / Daniel Flippo / In 2050 the world’s population is projected to be over 9 billion people, creating a need for more agriculture production than ever before. One way to increase production of crops is to get them planted in an optimum planting window. This allows the crops to take the most advantage of the longer days during the growing season thus increasing their yield. The growing size of farms and reduced amount of farmers puts more pressure on each remaining farmer to mechanize more heavily, and to get more acres planted faster in order to get crops planted in time. Most areas have an optimal planting window of a few weeks. This drives a need for planters to get bigger so one man can plant more acres in a day. Besides getting bigger, planters are also getting able to accurately plant faster. Today many of the new planters are “high speed,” meaning they are able to plant at speeds of 7 to 10 mph. The typical research and discussions of high speed planters tend to focus on the speed effects on the seed placement, emergence, planting rates, active downforce systems, metering systems etc. There is little discussion on the effects these higher planting speeds have on the draft requirements of the row unit itself. There needs to be more knowledge about the relationship between soil and planting tools in order to optimize power and performance of the tools to minimize fuel consumption, labor, and soil compaction. In order to test the draft forces of various tillage and planting tools in different field conditions there needs to be a machine that can repeatedly test multiple tools in multiple field conditions over a wide range of speeds. This paper is about the development of such a machine. The Cultivation Assessment Test Apparatus (CAT App.) is a device used to pull tillage and planting tools at a consistent depth at different speeds measuring the draft and downforce requirements during tests.

The effects of a straw mulch, applied either uniformly or in strips, on the surface energy balance and soil thermal regimes are investigated using a numerical solution to the two-dimensional soil heat transfer equation. The numerical technique used is an extended version of Barakat and Clark's (1966) alternating direction explicit method. The modified technique can solve problems that are periodic in time and/or space, on either rectangular domains or domains with a curvilinear upper boundary, and in which the soil thermal properties may vary with position, time, or temperature. The method also incorporates non-uniform grid spacings to reduce computation time and to increase efficiency. The straw mulch is represented as a single layer of constant shortwave and longwave transmissivities and reflectivities. Vertical transport of heat and water vapour through the mulch is evaluated by bulk transfer equations. Shading of the bare strip and reflection of radiation onto it by the sides of the mulch strip, as well as the reduction of the sky-view factor seen by the bare strip, are included. Solar irradiance, air temperature and water vapour density, wind speed, soil thermal properties and mulch parameters are the required inputs. Evaporation is estimated using a surface resistance model to vapour flow. The model is compared with micrometeorological measurements made in soils covered with barley straw, either uniformly at rates of 2, 10 or 20 t/ha or in 0.30 m wide mulch strips (10 t/ha rate) alternating with 0.10 m wide bare strips, with the strips oriented in north-south, northeast-southwest, or east-west directions. The results show that for the uniformly applied mulch soil temperatures can be adequately predicted but evaporation is underestimated. Both soil temperatures and evaporation are underestimated in the bare strip. The differences are attributed to the penetration of wind eddies into the straw mulch and the microscale advection from the warm straw strips onto the relatively cold bare strips. / Land and Food Systems, Faculty of / Graduate

Pineview clay originates from a lacustrine deposit and has a clay content of approximately 55%. During the spring the soil is generally quite moist due to melting snow and rainfall, while ambient air temperatures are relatively cool. These factors cause soil warming on Pineview clay to be slow. Due to the slow soil warming process in the spring and due to the fine texture of this soil, it is important that the Pineview clay maintains a good soil structure. Little research has been carried out on Pineview clay as to the effect of tillage practices on soil structure. It was the purpose of this project to study changes in the properties of Pineview clay brought about by different tillage systems. In the first part of the project major adverse soil conditions that occur on Pineview clay were evaluated with respect to the emergence of barley. In the laboratory the effects of soil compaction and soil temperature were evaluated in terms of barley seedling emergence. The second part of the study consisted of determining the feasibility of several tillage systems and the use of a herbicide prior to tillage on Pineview clay. In the last part of the study four fall sod breaking tillage systems were evaluated in terms of their effect on soil physical properties, N transformations, crop growth and development, and economic returns. Barley seedling emergence in the laboratory was found to be affected by soil compaction and soil temperature. Between 5⁰ and 20⁰C the rate of barley emergence approximately doubled for every 5⁰C increment in soil temperature. Applying the herbicide Gramaxone prior to tillage improved soil break-up and control of sod regrowth, but the cost of this herbicide may be prohibitive. For sod breaking operations a stubble plow proved to be inadequate and a special sod breaking plow should be used. Rotovation prior to moldboard plowing improved soil break-up and control of sod re-growth. Chisel plowing resulted in a rough, mulched soil surface condition, which required many passes before a satisfactory level soil surface had been created. The four fall sod breaking systems were moldboard plowing (using a sod breaking plow) with and without prior rotovation, and chisel plowing with and without prior rotovation. The results indicate major differences due to the type of plow used (moldboard vs chisel) rather than the additional use of the rotovator prior to plowing. Moldboard plowing resulted in superior soil physical conditions, higher soil NO₃-N levels, higher crop yields and N uptake by the crop, and better economic returns than chisel plowing. The four tillage systems reached maximum profits under various fertilizer rates; $208.00/ha for moldboard plowing at 112 kg N/ha, $104.00/ha for rotovating and moldboard plowing at 56 kg N/ha, $71.00/ha for chisel plowing at 168 kg N/ha, and $39.00/ha for rotovating and chisel plowing at 0 kg N/ha. / Land and Food Systems, Faculty of / Graduate

Tillage practices on agricultural fields have an impact on not only the amount of soil erosion from the fields, but also on the hydrologic and other environmental characteristics of the land. This erosion takes away soil that is necessary for sustainable agriculture, and the sediment and nutrient removal from the fields can pollute surrounding waterbodies. The Llanos Orientales of Colombia used to be a region of extended savannas and native fragile ecosystems dedicated to extended cattle ranch that has been transitioning to crop production. Agricultural expansion in this area, involving mechanization, could importantly accelerate the degradation of soils, limiting the development of sustainable agricultural systems. As a first step to understand long term effects of different tillage practices on new agricultural areas in the region, this study aims to evaluate the performance of the Agricultural Policy Environmental eXtender (APEX) model to simulate runoff, soil erosion and crop yield from fields under conventional tillage, reduced tillage, and no tillage in the Llanos Orientales of Colombia. Calibrated APEX model predictions were compared against measured runoff, soil loss and crop yield data from row crop plots established in the Experimental Station la Libertad in Colombia under conventional, reduced and no-tillage management. APEX satisfactorily predicted runoff (Nash Sutcliffe Efficiency NSE>0.53, Percent Bias - [PBIAS] < 21%) and crop yield for all three tillage systems (NSE>0.82, [PBIAS] <15%), but was not successful in predicting soil loss from the studied plots. Unsuccessful results were related to model limitations to predict erosion (USLE equations), but also to any uncertainty attributed to issues in the data collection. A calibrated APEX model could be used to predict runoff and crop yield responses under different management practices in the Llanos Orientales of Colombia, but needs improvements for prediction of soil erosion in tropical soils.