Economic impacts of soil erosion in Iowa

Everyone agrees that soil erosion is detrimental to Iowa agriculture. This study attempts to quantify the effects of erosion on contemporary crop yields and gauge the longer term impact on the agricultural economy in the state

Geochemistry of hydrothermal vent fluids from the northern Juan de Fuca Ridge

Submitted in partial fulfillment of the requirements for the degree of Doctor of Philosophy at the Massachusetts Institute of Technology and the Woods Hole Oceanographic Institution February 2003The presence of aqueous organic compounds derived from sedimentary organic matter has the potential to influence a range of chemical processes in hydrothermal vent environments. For example, hydrothermal alteration experiments indicate that alteration of organic-rich sediments leads to up to an order of magnitude more metals in solution than alteration of organic-poor basalt. This result is in contrast to traditional models for the evolution of vent fluids at sediment-covered mid-ocean ridge axis environments, and indicates the fundamental importance of including the effects of organic compounds in models of crustal alteration processes. However, in order to rigorously constrain their role in crustal alteration processes, quantitative information on the abundances and distributions of organic compounds in hydrothermal vent fluids is required. This thesis was undertaken to provide quantitative information on the distributions and stable carbon isotopic compositions of several low-molecular weight organic compounds (C1-C4 alkanes, C2-C3 alkenes, benzene and toluene) in fluids collected in July, 2000, at three sites on the northern Juan de Fuca Ridge: the Dead Dog and ODP Mound fields, which are located at Middle Valley, and the Main Endeavour Field, located on the Endeavour segment. At Middle Valley, the ridge axis is covered by up to 1.5 km of hemipelagic sediment containing up to 0.5 wt.% organic carbon. The Main Endeavour Field (MEF) is located approximately 70 km south of Middle Valley in a sediment-free ridge-crest environment, but previously measured high concentrations of NH3 and isotopically light CH4 relative to other bare-rock sites suggest that the chemical composition of these fluids is affected by sub-seafloor alteration of sedimentary material (LILLEY et al., 1993). Differences in the absolute and relative concentrations of NH3 and organic compounds and the stable carbon isotopic compositions of the C1-C3 organic compounds suggest that the three fields represent a continuum in terms of the extent of secondary alteration of the aqueous organic compounds, with the Dead Dog fluids the least altered, the MEF fluids the most altered and ODP Mound fluids in an intermediate state. At the two Middle Valley sites, the greater extent of alteration in the ODP Mound fluids as compared to the Dead Dog fluids is due either to higher temperatures in the subsurface reaction zone, or a greater residence time of the fluids at high temperatures. Higher reaction zone temperatures at the ODP Mound field than at the Dead Dog field are consistent with differences in endmember C1 concentrations between the two fields. The greater extent of alteration in the MEF fluids is caused by relatively oxidizing conditions in the subsurface reaction zone that promote faster reaction kinetics. Temperatures in the subsurface reaction zones calculated by assuming equilibrium among aqueous alkanes, alkenes and hydrogen are consistent with other inorganic indicators (C1 and Si concentrations) of temperature, indicating that metastable equilibrium among these compounds may be attained in natural systems. Isotopic equilibration among CH4 and CO2 appears to have been attained in ODP Mound fluids due to the high temperatures in the subsurface reaction zone and the approach to chemical equilibrium from excess methane. However, isotopic equilibrium between CH4 and CO2 was not attained in the MEF fluids, due to a short residence time of the fluids in the crust following late-stage addition of magmatic-derived CO2 to the fluids. Time series analysis indicate that Middle Valley fluid compositions are generally characterized by stable concentrations over the last decade. However, decreases in Br concentrations in Dead Dog fluids from 1990 to 2000 suggest that either a greater proportion of the fluids interact with basalt rather than sediments or that the sediment with which hydrothermal fluids interact is becoming exhausted. In contrast, the concentrations of H2 and H2S and the δ34S of H2S are quite different in fluids sampled from vents of differing ages at the ODP Mound field, despite their close spatial proximity. The observed variations are caused by the reaction of hydrogen-rich fluids within the ODP Mound massive sulfide to reduce pyrite to pyrrhotite during upflow. The replacement of pyrite by pyrrhotite is opposite to the reaction predicted during the weathering of sulfide minerals weather on the seafloor and reflects the real-time equilibration of the reduced fluids with mound mineralogy due to the very young age (<2 years) venting from Spire vent. The presence of aqueous organic compounds therefore affects not only the inorganic chemical speciation in vent fluids, but can also control the mineralogy of associated sulfide deposits. These results also indicate that vent fluid compositions do not necessarily reflect conditions in the deep subsurface, but can be altered by reactions occurring in the shallow subsurface.This research was supported by grants to Jeffrey Seewald from the Petroleum Research Fund (323lO-AC2), administered by the American Chemical Society, the National Science Foundation (OCE-9618179, OCE-9906752, OCE-0136954) and the WHOI Green Technology Fund

Nitrogen management alternatives for ridge tillage corn

As soil and resource conservation become dominant themes in modern agriculture, researchers seek practices that will maintain profitability while reducing inputs. Ridge tillage, which has received increasing attention as an alternative to the flat-surface, no-till system, may be one such practice

Higher Population and Twin Row Configuration Does Not Benefit Strip Intercropped Corn

Increased corn (Zea mays L.) grain yield with strip intercropping, made possible because of increased edge effects, makes this soil-conserving crop production system appealing to farmers. The objective of this study was to determine the population and row configuration needed to optimize the additional yield potential in each outside corn row. Treatments \u27included: 74, 99, and 124 thousand plants ha-1 were grown in twin rows and 74 thousand plants ha-1 grown in single rows. Single rows or twin row centers were spaced 0.76 m. The experiment was conducted at four central Iowa sites during 1996 and 1997. Grain yield was not increased by increasing population, nor did it respond consistently to the twin row configuration. There was little interaction between row position in the strip and treatment response. Higher plant population decreased the number of ears per plant, kernels per row, and kernel weight. The twin row configuration increased the number of ears per plant, but this was offset by a decrease in the number of kernels per row and kernel weight. Farmers should follow current cropping recommendations until this optimum is determined. Given the inconsistent grain yield response to twin rows, there is no current rationale for investing in twin row planting equipment

Southeast Iowa on-farm demonstration of sustainable tillage systems and weed profile developments on those systems

This study was designed to determine whether tillage systems left in place for significant periods of time develop different weed profiles. No-tillage, reduced tillage, and conventional tillage were placed in a corn/soybean rotation that had been maintained and documented for 15 years. Notillage was the only corn tillage treatment that did not lead yields for at least one year of this three-year trial. No-tillage corn had significantly higher weed pressure from several species, and soybeans had significantly higher levels of giant foxtail with no-tillage. The study also compared ridge and reduced tillage yields and weed profile development; the third year of the study constituted the eighth year that those systems were in place. Ridge tillage soybeans had higher yields and significantly higher weed pressure for a number of species; no trends were detected for corn yields or weeds

Effectiveness of vegetative filter strips

The use of close-growing plants, such as in grass sod, is a long-established technique for controlling soil erosion. This approach serves two purposes: (1) the fine root system of sod holds soil in place, thereby reducing its susceptibility to erosion, and (2) the plants slow the velocity of water flow, which reduces the sediment-carrying capacity of the wate

Corn (Zea mays L.) Yield Response to Nitrogen Fertilizer in Conventional and Alternative Rotations

Nitrogen (N) fertilization recommendations are not available for corn in rotation with small grains or forages despite the possibility that the N response may differ from that of more conventional corn-soybean rotations. Rotations of corn with soybean (CS), corn with soybean and oat (CSO) and corn with soybean and an oat/berseem clover intercrop (CSOB) were established in 1991 and studied from 1993 through 1998 to determine the optimal N fertilization level for corn produced in each rotation. Corn in each rotation received NH4N03 applied at the rates of 0, 56, 112, or 168 kg N ha-1. Significant differences in corn grain yield occurred between rotations in three years, but no rotation was consistently superior. Corn grain yield increased with N fertilizer in each year, but in 3 of 6 years there was no advantage to applying Nat a rate greater than 112 kg ha-1. No difference in N response between rotations was observed

Getting Published: Inquiring Minds Want to Know

With something as career-significant as your scholarly plan, you would probably feel more certain if you received advice from more than one source - albeit the Co-Oracles of Richmond. To satisfy your desire for corroboration (a necessary disposition for a scholar-researcher), we\u27ve gathered sage comments from colleagues from hither and yon concerning approaches to becoming a publishing scholar. You\u27ll note that their comments often overlap - and that\u27s a positive thing since such repetition affirms the strategy\u27s validity and helps you learn it. Our colleagues come from a variety of disciplines and positions - some are administrators and some reside outside the purely academic zone - but all have successfully published, many outside of their discipline

Getting Published: Inquiring Minds Want to Know

With something as career-significant as your scholarly plan, you would probably feel more certain if you received advice from more than one source - albeit the Co-Oracles of Richmond. To satisfy your desire for corroboration (a necessary disposition for a scholar-researcher), we\u27ve gathered sage comments from colleagues from hither and yon concerning approaches to becoming a publishing scholar. You\u27ll note that their comments often overlap - and that\u27s a positive thing since such repetition affirms the strategy\u27s validity and helps you learn it. Our colleagues come from a variety of disciplines and positions - some are administrators and some reside outside the purely academic zone - but all have successfully published, many outside of their discipline

Profitability of Crop Rotations in Iowa in a Stress Environment

Small grains crops have traditionally been included in Midwestern cropping systems, but their use is restricted by uncertain yields, poor prices, and lack of on-farm uses in operations without livestock. We compared the corn (Zea mays L.)-soybean (Glycine max (L.) Merr.) crop rotation to actual or simulated three-yr rotations at two sites in Iowa between 1986 and 1989. Water was generally more limiting than was nitrogen, which produced minimal response in the corn to which it was applied. April-November precipitation at Nashua, Iowa ranged from 59 to 111 % of average, while at Des Moines, Iowa it was 77% of normal in 1988 and 102% in 1989. Each rotation was subjected to economic analysis using Iowa State University figures for costs of operations and inputs. Commodity prices were set assuming nonparticipation in the government programs of the time. The rotations that depended on hay cuttings to recoup seeding costs never achieved that goal. Oat (Avena sativa L.) and wheat (Triticum aestivum L.) harvests did largely recover the cropping expenses of the systems that included them. Thus, in certain environments no sacrifice in short-term profitability is required in trade-off for the long-term conservation and economic benefits of diversified rotations