Assessing tillage- and cropping-induced changes in relative conductivity

Abstract

Although changes in relative hydraulic conductivity(K_rc) in the surface soil layer can have significantimpact on transport of water and solutes below this layer, experimentaldetermination of K_rc is laborious and expensive. In thisstudy, a simple theoretical equation has been used to compute near-surfaceK_rc and assess its sensitivity to tillage- andcropping-induced near-surface changes in soil porosity (.epsi;), porecontinuity (PC), and soil water content (&thgr;). The data were collected in1994 from a cropping and tillage system experiment established in 1988 on asilt loam soil. The tillage treatments were conventional and no-till. Thecropping treatments were continuous corn (Zea maize L.)under conventional cultivation (CT corn), corn following forages(alfalfa,Medicago sativa L.; and bromegrass,Bromus inermis L.) under conventional and no-till (NTcorn) practices, and continuous no-till corn. Soil bulk density (r ) and inthe near surface (depth, 0-2 ·5 cm) soil layer were measured in lateJuly 1994 subsequent to changes in tillage and cropping practices in May 1994.Only tillage differences had significant influence on ρ, &thgr;, fractaldimension (D), PC, and K_rc of the near-surface soillayer. A switch from no-till forages to CT corn resulted in increases in andD, and decreases in ρ , &thgr;, and K_rc. Theintroduction of NT corn into forage-terminated plots did not producesignificant changes in the above properties compared with continuous NT corn(7 years old), which was characterised by smaller values of and PC, and high&thgr; and K_rc. Water content, , and PC accounted for96% of the variability in K_rc. The results showedthat the near-surface changes in K_rc can be predictedwith high accuracy using the data on only ρ and &thgr; which are easy togather.