Soil Water Recharge under Uncropped Ridges and Furrows

Abstract

Nitrate leaching to ground and surface water is an increasing concern in agriculture. Ridge tillage and associated residue management offer potential for modifying the pattern of soil water and solute movement to reduce NO3 leaching from corn (Zea mays L.) production. To test this idea we used time domain reflectometry (TDR) measurements of volumetric soil water content (θ) at 0.5‐h intervals following natural rainfall events to determine the pattern of infiltration and soil water recharge for uncropped row and furrow positions in long‐term ridge‐tillage fields. Soil water content was measured under adjacent rows and three adjoining furrows for 103 d in 1992 on a Clarion loam (fine‐loamy, mixed mesic, Typic Hapludoll) near Boone, IA and 96 d on Monona silt loam (fine‐silty, mixed mesic, Typic Hapludoll) near Treynor, IA. During rainfall, infiltration occurred primarily in furrows, as indicated by greater and more rapid initial increases in θ for furrow than for row positions at the same elevation. Following redistribution and evaporation, row and furrow positions at the same elevation had θ values differing by <0.03 m3 m−3 Changes in profile average θ of rows and furrows between rainfall events were closely correlated (R2 > 0.94). Storage between rainfall events decreased with increasing initial θ and time interval between events (R2 > 0.68), consequently soil water recharge occurred as a series of stepwise increases of θ. These results support the conclusion that water infiltrated in furrows and primarily moved laterally to row positions, minimizing downward water movement under the row. These results explain greater solute movement under furrows than under rows, as found in several short‐term studies.