SEASONAL PATTERNS OF WATER AND CHEMICAL MOVEMENT IN TILLED AND NO-TILL COLUMN LYSIMETERS

Decreased runoff from no-till fields combined with preservation of macroporosity increases the potential for transport of agricultural chemicals to groundwater. Our objective was to determine if macropores affect the movement of water and surface-applied chemicals through the solum. Eight, 75-cm-long, 30-cm-diam. soil cores were obtained from a 17-yr-old, no-till, corn (Zea mays L.) field within a mapping unit of Rayne silt loam (fine-loamy, mixed, mesic Typic Hapludult). The cores were converted into column lysimeters and simulated tillage was performed on the upper 15 cm of four columns. The unvegetated columns were buried outside in a mowed area and received broadcast applications of NH4NO3 and SrBr2.6H2O each spring. During a 2-yr period, the no-till columns transmitted 36% more water than the tilled columns. Yearly total amounts of Br- and NO3- in the percolate were unaffected by tillage, although the losses during the growing season were greater for the no-till columns. Tillage had a greater relative effect on cation than on anion movement with losses of Sr2+ and NH4+ that were 2.6 and 6.6 times greater, respectively, for the no-till than for the tilled columns. The largest differences in chemical transport and percolate volume among tillage treatments were noted in the first few rainfalls after chemical application and during the summer months when potential evaporation was high. More rapid Br- and NO3- movement and greater Sr2+ and NH4+ movement in the no-till columns were attributable to preferential flow in macropores.