EFFECTS OF CONSERVATION PRACTICESON WATER QUALITY AE 520 Carl E Anderson Spring 2005
SOIL CONSERVATION PRACTICES • TERRACES AND DIVERSIONS • VEGETATED WATERWAYS • SEDIMENT RETARDING PONDS • CONTOURING • STRIP CROPPING • BUFFER STRIPS
EFFECTS OF CONSERVATION PRACTICESON WATER QUALITY • Any practice which reduces erosion will usually reduce transport of sorbed chemicals from a field. • Any practice which slows down the rate of surface runoff will increase infiltration, reduce chemical transport in runoff water, and increase chemical leaching to groundwater.
TERRACES AND DIVERSIONS • PURPOSE: • To slow down the flow velocity by forcing the water to follow a flatter path off the field. • To break a field up into small watersheds so that the water isn't concentrated until it reaches the edge of the field.
TERRACES AND DIVERSIONS • FUNCTION: Terraces and diversions tend to reduce the volume of surface runoff and erosion and increase the volume of infiltration. • They would tend to reduce the pollution of surface waters and increase the pollution potential of groundwater. • For chemicals such as most herbicides, which are strongly adsorbed on the soil particles, the net result should be lower overall water pollution.
VEGETATED WATERWAYS: • PURPOSE: To provide an outlet for concentrated flows from a field, particularly from a system of terraces or diversions. • FUNCTION: For the more common rainfall events, vegetated waterways may have some effect of filtering the runoff water, and of providing opportunity for infiltration. For strongly adsorbed chemicals, the result should be less pollution.
SEDIMENT RETARDING POND: • PURPOSE: To trap sediment that has eroded from the watershed and keep it from moving further downstream. • FUNCTION: Since sediment ponds tend to trap mostly the course material from the eroding soil, they would not have a great effect on the water quality leaving the field.
CONTOURING: • PURPOSE: The purpose of contouring is to establish tillage tracks across the normal flow path for surface runoff. These function as many, very small, closely spaced terraces on the field. The effects of contouring are most pronounced on middle range slopes (2% to 8%), and are not very important on very flat or very steep slopes. • FUNCTION: The primary effect of contouring on water quality would be to reduce chemical losses with erosion. There would also be some effect of increased infiltration, particularly from smaller storms. This would tend to reduce the pollution potential from chemicals which are strongly adsorbed.
STRIP CROPPING: • PURPOSE: The purpose of strip cropping is to provide alternating strips of open-tilled and close growing crops across the slope to reduce soil erosion. Strip cropping can only be used in a rotation which includes both open-tilled and close growing crops. • FUNCTION: Contouring will primarily affect the transport of adsorbed chemicals with eroding soil. There will also be some effect due to the reduced area treated with a given chemical because of the rotation.
BUFFER STRIPS: • PURPOSE: The purpose of buffer strips is to provide a natural filter for overland flow before it enters a stream channel. A secondary benefit is to eliminate the application of chemicals to the riparian lands of a stream channel. • FUNCTION: Since most of the flows enter a stream channel at a point of concentrated flow, the secondary benefit mentioned above is probably the only real effect on water quality in most situations.
CHEMICAL CONSERVATION MEASURES • Any measures which reduce the amount of chemical applied to the field will reduce the potential for water pollution from that chemical. • REDUCE THE NUMBER OF CROPS RECEIVING AN APPLICATION • Only apply chemical when it is absolutely needed. Use soil tests for nutrients, and scouting information for pests. • REDUCE THE AREA OF APPLICATION • Use controlled application methods such as banding of nutrients and herbicides.
CHEMICAL CONSERVATION MEASURES • REDUCE THE RATE OF APPLICATION • HANDLE ALL CHEMICALS IN A SAFE AND REASONABLE MANNER • Store, handle, and mix all chemicals well away from all active or abandoned wells, ponds, and streams. Dispose of cleaning water and empty containers in a safe manner.
WATER QUALITY CONTROL PRINCIPALS • On a field where chemicals are used, runoff carries chemicals to surface streams, ponds, and lakes and infiltration carries chemicals to ground water. • Practices which reduce runoff water pollution will tend to increase leaching to ground water and visa versa.
WATER QUALITY CONTROL PRINCIPALS • Polluted ground water is harder to clean up than surface water. Therefore, if a choice must be made, protect ground water at the expense of surface water quality.
WATER QUALITY CONTROL PRINCIPALS • Reduce the amount of chemical applied • use lower application rates • use controlled placement methods • use chemicals with shorter half-life
WATER QUALITY CONTROL PRINCIPALS • Reduce the contact between the chemical and water • Keep chemicals out of waterways • Keep chemicals out of low spots where the water ponds and infiltrates • Time applications to avoid rainfall and runoff
WATER QUALITY CONTROL PRINCIPALS • Chemicals are decomposed more rapidly at or near the field surface • Use chemicals that are strongly adsorbed on the soil • Use practices that keep most chemical near the surface