Nutrient loadings to the Chesapeake Bay are a source of concern for water quality agencies. In particular, excess nitrogen loadings from agricultural production activities threaten water quality in the Bay. Questions have been raised about how effectively traditional BMPs can control nitrogen loss from crop production. This study examines agricultural nitrogen pollution control from an input management perspective. Using an economic and physical model, seven production systems and nitrogen management strategies are compared in terms of input use, profitability, and nitrogen loss potential. Results suggest that several of the production systems will reduce residual nitrogen without reducing profits. However, it is recognized that factors in addition to profitability will influence producers' nitrogen management decisions. Therefore, using the results of a farmer survey, adoption models are estimated to examine the impact of production system characteristics and producer characteristics on the decision to use an alternative production system and nitrogen management strategy. Finally, a sensitivity analysis is conducted to examine the impact of alternative policy tools on adoption incentives. Both financial incentives and education and information programs are found to be important tools for influencing producers' decisions. Producers' interest in the alternative systems and desire for information on the systems suggest that agricultural research will contribute by assuring that producers have access to adequate information on the alternative systems. / Ph. D.

The MANIMEA $ rm ( underline{MA}nurial underline{NI}trogen underline{M}anagement{:} underline{E}nvironmental underline{A}spects)$ model is a one-dimensional dynamic model that simultaneously simulates nitrogen transformations (volatilization, net mineralization-immobilization, and denitrification), nitrogen transport (runoff and leaching), plant uptake, and adsorption in homogeneous, unsaturated soils. The simulated system is divided into two components: the applied manure layer and the soil. The model describes the transformation processes occurring in both components separately. It is also capable of accounting for both micro and macroporous flows. In addition, the simulation can be done for time steps shorter than 1 day. / The model was developed to be interactive and user-friendly and was constructed on a modular basis using Microsoft FORTRAN PowerStation$ sp circler$ as a compiler. It can be run on an IBM$ sp circler$ or IBM compatible microcomputer with a minimum requirement of a 386 microprocessor with 4 MB RAM. This model was developed as a nitrogen management-oriented model. However, it can also be used to gain further understanding of nitrogen processes for research and teaching purposes. / The accuracy of the stimulation was enhanced by taking into account moisture and temperature variation and distribution in the soil. The SWACROP and the HEAT programs were integrated into the MANIMEA model to generate transient moisture and temperature profiles, respectively. The Numerical Method Of Lines (NMOL) technique, which implements finite difference method, was used to numerically solve the partial differential equations in the model. / Generally, the results generated by the MANIMEA model using the parameters from literature agreed with the results obtained by analytical solutions and from experiments. It was found that the model is highly sensitive to the volatilization and net mineralization rate constants $(K sb{v}$ and $K sb{m}).$ The study showed that the MANIMEA model can be implemented to evaluate nitrogen transformations, transport, and plant uptake for a wide range of climatic and soil conditions and organic type of wastes. Such a tool can contribute to the protection of our environment through a better management of organic nitrogen fertilizer and a better understanding of the nitrogen processes.

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