some practices designed to minimize negative impacts of farming practices on water quality can worsen problems with air quality. That point can be illustrated by the use of riparian zones and treatment wetlands. They can reduce nitrogen fluxes into surface waters in part by increasing rates of denitrification. However, the process of denitrification does not always result in the complete conversion of nitrate to nitrogen gas, in which case various potent greenhouse gases, nitrogen oxides, are produced; thus, a tradeoff exists between improving water quality and air quality (Crumpton et al., 2008). While riparian buffer strips are designed to reduce negative effects of crop farming on nearby water bodies and are beneficial in most extensive cropping systems, there are concerns that they provide habitats for wildlife that might defecate in the crop fields and contaminate vegetables and fruits that are consumed fresh (Atwill, 2008; Doyle and Erickson, 2008).

Contentious tradeoffs can also occur between environmental, social, and economic goals. Examples include production of food to feed a growing world population versus a desire to use production practices that protect soil, air, water, and biological resources and preserve some resources for nonfood production uses such as wildlife habitat. Efforts to use environmentally friendly practices or to improve the economic conditions of farmers or farm workers can sometimes increase production costs and possibly hinder access to affordable healthful food among low-income consumers. Opinions differ widely as to whether those goals necessarily are in direct conflict, or the extent of tradeoffs involved, but nonetheless balancing the different goals clearly has to be addressed.

Another potential tradeoff could be between the ability of a system to produce the outputs desired by society (for example, food, fiber, and fuel) and the resilience and resistance of that system. For example, diverse farming systems with multiple crops or integrated systems with livestock might be more able to sustain reasonable production and profit in the face of climatic or market volatility, but they might be less productive when measured by volume of production or by profits in “normal” or optimal years. However, the more variable and unpredictable conditions become, then the argument for trading some degree of maximum productivity, or efficiency, for greater stability becomes stronger (Walker and Salt, 2006). In the case of agriculture, that tradeoff may mean sacrificing the ability to achieve maximum yields and income in good years in return for a system that performs well over a wide range of conditions and is less likely to fail in bad years. Managing a system to achieve high yields clearly is an important component of sustainability, but maximizing one component can come at the expense of overall system resilience, which in turn reduces overall sustainability. (See Walker and Salt, 2006, for illustrative examples.) As used above, the term “efficiency” reflects efforts to maximize input use efficiency per unit production. In the rest of this report, the term “efficiency” is sometimes used with a similarly narrow definition (as in the case of the discussion on water use efficiency in Chapter 3). Other times, the term is used in the broad context of “systems efficiency” to reflect the notion of minimizing undesired outcomes (such as pollution and waste) from resource use while maximizing a wide group of desired outcomes (which could include production and support for important ecosystem services) and reducing the need for external inputs (which could be achieved by increasing nutrient cycling between animal and crop production).

SETTING PRIORITIES FOR AGRICULTURAL SUSTAINABILITY

Who Decides?

Any single farming system is unlikely to meet fully all of society’s production, environmental, economic, and social goals and objectives. Indeed, it is most probable that meeting many of society’s goals will require a mixture of many farming types and systems rather



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