The final phase of the agricultural water use cycle is discharge, in which water returns by runoff or seepage to the larger hydrologic cycle. As described in Chapter Two, this phase is a problem inasmuch as the discharges carry pollutants like nitrates and pesticides.
Since agriculture is a non-pointsource polluter its output generally cannot be collected and treated. Therefore, those solutions typically applied to industrial and municipal polluters are not useful in an agricultural setting. Some agricultural pollution problems can be mitigated by the adoption of best management practices (BMPs), which are the primary options available to alleviate non-pointsource pollution. However, most BMPs are not technology-based, in the traditional sense of ``technology.'' BMPs include tilling fields less frequently, or planting alternating rows of corn and beans, or placing ditches where sediment will collect rather than run off into streams (Gale et al., 1993).
The more traditional technological options available to the farmer focus on requiring less pesticides. Crops can be genetically engineered to require fewer pesticides, and new pesticides can be developed that are more environmentally friendly. A spokesman for Novartis, a biochemicals company, asserts that ``[b]y just isolating the active isomer, we have been able to reduce the application rate of an established Novartis active ingredient by 50% and achieve the same fungicidal effect'' (Samo, 1997). However, some bioengineered products may lead to increased pesticide applications; for instance, Monsanto's ``Roundup Ready'' line of soybeans has been made resistant to the pesticide, effectively raising the maximum amount that can be applied to a field (Altieri and Rosset, 1999).
Bioengineering options are generally areas for future research; there is presently no clear technological solution to the issues of polluted agricultural discharges.