Yield potential and resource-use efficiency of maize systems in the western U.S. Corn Belt

Maize demand for food, livestock feed, and biofuel is expected to increase substantially. The Western U.S. Corn Belt accounts for 23% of U.S. maize production, and irrigated maize accounts for 43 and 58% of maize land area and total production, respectively, in this region. The most sensitive parameters (yield potential [YP], water-limited yield potential [YP-W], yield gap between actual yield and YP, and resource-use efficiency) governing performance of maize systems in the region are lacking. A simulation model was used to quantify YP under irrigated and rainfed conditions based on weather data, soil properties, and crop management at 18 locations. In a separate study, 5-year soil water data measured in central Nebraska were used to analyze soil water recharge during the non-growing season because soil water content at sowing is a critical component of water supply available for summer crops. On-farm data, including yield, irrigation, and nitrogen (N) rate for 777 field-years, was used to quantify size of yield gaps and evaluate resource-use efficiency. Simulated average YP and YP-W were 14.4 and 8.3 Mg ha-1, respectively. Geospatial variation of YP was associated with solar radiation and temperature during post-anthesis phase while variation in water-limited yield was linked to the longitudinal variation in seasonal rainfall and evaporative demand. Analysis of soil water recharge indicates that 80% of variation in soil water content at sowing can be explained by precipitation during non-growing season and residual soil water at end of previous growing season. A linear relationship between YP-W and water supply (slope: 19.3 kg ha-1 mm-1; x-intercept: 100 mm) can be used as a benchmark to diagnose and improve farmer’s water productivity (WP; kg grain per unit of water supply). Evaluation of data from farmer’s fields provides proof-of-concept and helps identify management constraints to high levels of productivity and resource-use efficiency. On average, actual yields of irrigated maize systems were 11% below YP. WP and N-fertilizer use efficiency (NUE) were high despite application of large amounts of irrigation water and N fertilizer (14 kg grain mm-1 water supply and 71 kg grain kg-1 N fertilizer). While there is limited scope for substantial increases in actual average yields, WP and NUE can be further increased by: (1) switching surface to pivot systems, (2) using conservation instead of conventional tillage systems in soybean-maize rotations, (3) implementation of irrigation schedules based on crop water requirements, and (4) better N fertilizer management.

Environmental and Farm Management Factors Associated with Tuberculosis on Cattle Farms in Northeastern Michigan

Objective—To identify major environmental and farm management factors associated with the occurrence of tuberculosis (TB) on cattle farms in northeastern Michigan. Design—Case-control study. Sample Population—17 cattle farms with infected cattle and 51 control farms. Procedure—Each case farm (laboratory confirmed diagnosis of Mycobacterium bovis infection) was matched with 2 to 4 control farms (negative whole-herd test results within previous 12 months) on the basis of type of farm (dairy or beef) and location. Cattle farm data were collected from in-person interviews and mailed questionnaires. Wildlife TB data were gathered through state wildlife surveillance. Environmental data were gathered from a satellite image-based geographic information system. Multivariable conditional logistic regression for matched analysis was performed. Results—Major factors associated with increased farm risk of TB were higher TB prevalence among wild deer and cattle farms in the area, herd size, and ponds or creeks in cattle housing areas. Factors associated with reduced farm risk of TB were greater amounts of natural open lands in the surrounding area and reducing deer access to cattle housing areas by housing cattle in barns, barnyards, or feedlots and use of electrified wire or barbed wire for livestock fencing. Conclusions and Clinical Relevance—Results suggest that certain environmental and management factors may be associated with risk of TB on cattle farms.

Essays on Industrial Organization and Environmental Economics

This dissertation studies environmental regulation issues in the hog production industry as well as forces behind the reorganization of the industry during the past two decades. Federal and State-level environmental regulations imposed on U.S. hog production during the year 2003 are examined in Chapter 1. Based on the number of regulations passed by the Federal government and states, the 2003 regulatory index is constructed. The regulatory stringency index suggests that state-level regulations vary across states and have increased over the years. In addition, state-level regulations are more stringent than federal regulations. Chapter 2 develops an empirically implementable theoretical model which allows us to investigate the long-run effects of environmental regulations on the U.S. hog industry. Hog feeding operations (HFOs) are divided into large feeding operations (LHFOs) and small feeding operations (SHFOs). The impact of the presence of a large number of LHFOs on the entry and exit of CHFOs is also examined. Results of this study suggest that: Increased state-level regulation stringency significantly lowers the output of SHFOs; increased state-level regulation stringency significantly lowers the output of LHFOs; increased state-level regulation stringency significantly lowers the number of SHFOs; SHFO output rises significantly in states that have a greater number of LHFOs; LHFO output rises significantly in states that have a greater number of LHFOs; the number of SHFOs significantly increases in states that have a greater numbers of LHFOs; regulation increases the average SHFO size; and regulation decreases the average LHFO size. Chapter 3 examines the importance of input availability, market attractiveness, agglomeration economies and environmental regulations on the reorganization of U.S. hog production for a panel of 22 U.S. hog producing states which include, Northern states, Southern states and Midwest states for the period 1994-2006. Results from this study suggest that: Hog production in a state is positively affected by hog production in a nearby state, confirming the presence of agglomeration economies; Environmental regulations and high corn price have negative effects on state-level U.S. hog production; High hog prices, and favorable labor cost, and land values attract hog production; and transportation cost has no effect on hog production. Advisors: Azzeddine Azzam and Karina Schoengold