Agricultural chemical management practices to reduce losses due to drainage

Chemical losses with water and sediment are a product of the mass of carrier and chemical concentration in that carrier. One approach to controlling losses is to utilize chemical management practices that reduce the chemical concentrations in the water and sediment that leave a treated field; another is to control the masses of the carriers. In this paper, emphasis will be placed on the former, with a discussion of rate, timing, placement, and choice-of-chemical options available for the application of fertilizers and pesticides and their effect on offsite losses with surface and subsurface drainage. Particular emphasis will be on the known effects of application variables on nitrate-nitrogen (NO3-N) leaching and on herbicide losses in both surface runoff water and sediment and with percolation water. Current understanding of chemical transport processes will be used to extrapolate to situations in which actual data are not available. Areas of research to fill these data gaps and to improve our understanding of the effects of current management practices on losses and also to develop new chemical management practices to increase further the efficiency of use and reduce losses will be addressed. The usefulness of standards, or some form of health advisory levels, as goals for levels of control necessary will also be noted.