Submitted to: Agricultural Water Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/21/2001
Publication Date: N/A
Interpretive Summary: When rainfall reaches the soil surface, some of the water runs across the soil and eventually into streams and lakes while some enters the soil. Water that enters the soil can later evaporate or move deeper into the ground until it reaches groundwater. Water that moves to streams of lakes and groundwater can carry chemicals like nutrients from manures or fertilizers with it. The amount and timing of water runoff and movement to groundwater was measured on a hillslope in the Ozarks. Most of the water from precipitation entered the soil and was later evaporated either from the soil or though the grass growing at the site. Only about 3% of the rainfall left the hillslope as runoff and all of this happened during 3 days in the winter. Movement to groundwater occurred over a longer period in winter and amounted to about 9% of the rainfall. These results indicate that wet soil conditions encourage water movement to streams, lakes, and groundwater so manure should not be applied when the soil is wet or rainfall is likely to occur soon. This information can be used by owners of animal feeding operations to help schedule the timing of manure applications that will reduce the risk of nutrient transport from their fields.
Technical Abstract: Movement of water, either as surface runoff of groundwater recharge, is the primary mechanism of transport for nutrients and agrichemicals in the terrestrial environment. The objective of this study was to determine the timing and amount of surface runoff and groundwater recharge for a hillslope receiving poultry litter (manure plus bedding) in the Ozark Highlands of the U.S. A 0.4-ha watershed having tall fescue (Festuca arundinacea Schreb.) cover was established at a site in northwestern Arkansas (35 degrees 56' W, 93 degrees 51' N)in 1994 for the purpose of sampling surface runoff. Additional hydrologic instrumentation was added in 1997 and continuous measurements were made from June 1997 to August 1998 to estimate groundwater recharge as the residual of weekly water balance calculations. Over the 14-month measurement interval, runoff occurred on only 3 days in January 1998 and totaled 30.6 mm of water (2.6% of the 1185 mm of precipitation at the site). Groundwater recharge totaled 117 mm and occurred primarily during an 83-day interval in the winter of 1998. The water balance was dominated by evaporation, which accounted for 91% (1080 mm) of the precipitation. Tall fescue was capable of sustaining relatively high evaporation rates between infrequent summer rains thereby dewatering the soil profile which was not replenished until winter. Under the conditions of this study, surface runoff and significant groundwater recharge occurred only in the winter when the soil was wet and evaporation was limited.