An awareness of the effect of agricultural production on the environment has led to the development of policies to mitigate its adverse effects. This dissertation provides analyses of agri-environmental policies designed to protect environmental assets, as well as analytical decision-making tools useful for conducting policy evaluations. The first essay employs propensity score matching techniques to estimate the additionality of federal agricultural conservation programs for six conservation practices for farmers in Ohio. Additionality is an important measure of the effectiveness of conservation programs in inducing an increase in the conservation effort of farmers. Results suggest that additionality is positive and statistically significant for all six conservation practices. However, while programs achieve positive additionality for all practice types, a comparison between conservation practices reveals that certain practice types achieve higher percent additionality than others. Such results, coupled with information on the environmental benefits obtained per practice, could prove useful to program managers for improving the effectiveness of conservation programs. The second essay develops a new methodology to decompose the additionality measure into the two effects induced by conservation programs: expansion versus the new adoption of conservation practices. To do so, the relative contributions of two types of farmers, prior-adopters and new-adopters, are estimated. Results of the decomposition reveal that the additionality for prior-adopters is not significant for all practice types. Instead, additional conservation effort comes from new-adopters adopting new practices. Second, decomposition estimates suggest that practice types with a greater fraction of enrolled farmers that are new-adopters achieve greater percent additionality than those with greater proportions of prior-adopters. This suggests that a farmers? history in conservation adoption has a significant influence on additionality levels. The final essay analyzes the effect of recent instream flow diversion-guidelines on agricultural water security and streamflows within a decentralized water management regime. Spatially-explicit economic and hydrologic models are integrated to evaluate the tradeoffs between salmon bypass-flows and agricultural water security for three different diversion-guidelines within a northern-California watershed. Results indicate that the most restrictive diversion-guideline provides the greatest protection of bypass-flow days within smaller watersheds; however, within larger watersheds protection is not as significant. Water security, however, decreases sharply under the strict and moderate diversion-guidelines, especially during dry years. Overall, results indicate that greater focus should be given to protecting streamflows in the smallest watersheds, and meeting human water needs during dry years, when agricultural water security is impacted the most.