Management of subirrigation systems in humid regions to minimize agrochemical losses in runoff during rainfall events

Soil-water management for agricultural crops in the Southeastern U. S. depends upon many factors. A water table exists in the soil profile much of the year, especially during the spring and growing season, and thus a water table control (WTC) system is often feasible for managing soil-water. A common system in the Southeast uses dual-purpose subsurface conduits for subirrigation and controlled-drainage of the soil profile to maintain soil-water content in the root-zone. In coastal areas, where gravity drainage outlets are often not possible or practical, WTC system conduits are connected to sumps in which the water level is controlled by pumps rather than an overflow pipe outlet. Water is pumped out of the sumps for subdrainage and back into them from an external source for subirrigation. Water table control in the southeast is often difficult because of the erratic spatial and temporal distribution of rainfall. It is common for periods of excess and deficit soil-water conditions to occur during the same cropping season. WTC operational schemes are improved when the predicted probability and amount of rain included in weather forecasts are used to help schedule start and stop periods for operating in the subirrigation and controlled-drainage modes. As weather forecasts are improved, the proper use of the forecast information can aid in scheduling agrochemical applications to minimize the risk of losses in runoff and subsurface drainage discharge during subsequent rainfall events.