CHARACTERIZATION OF WATER TRANSMISSION PROPERTIES IN TILLED AND UNTILLED SOILS USING TENSION INFILTROMETERS

Tension infiltrometer (TI) measurements from a silty clay loam soil (Winchester, Ont.), a sandy soil (Hancock, WI), and a silt loam soil (Rosemount, MN) were used to: (i) characterise near-saturated hydraulic conductivity (K-0) and flow-weighted mean radius of soil macropores (R(0)); (ii) distinguish differences in these water transmission properties between no-till (NT) and mouldboard plough (MP) continuous maize (Zea mays L.) production systems. The K-0 values increased by about two orders of magnitude as the pressure heads (P-0) set on the TI membranes were increased incrementally from the minimum values (P-0 = -10 cm or -15 cm) to the maximum value (P-0 = 0 cm). This indicates that substantial networks of water-conducting soil macropores exist in continuous maize production systems, regardless of soil texture or tillage treatment. For each P-0 value, the MP treatment had a consistently higher K-0 than NT at the Winchester and Hancock fields sites, and a consistently lower K-0 than NT at the Rosemount field site. Regardless of soil type, most R(0) pores occurred in the 0.1-0.3 mm size range for both NT and MP soils, but NT had two to three times more of these R(0) pore sizes, as well as smaller and larger R(0) pores, than MP. This probably reflects a more consolidated soil matrix (enrichment of smaller R(0) pores) and a greater number of large cracks and biopores (larger R(0) pores) in NT soils, owing to the absence of annual loosening of the soil matrix and disruption of macropores that occurs with MP tillage. Relationships between K-0 and R(0) were complex but consistent within and between tillage treatments. A physical interpretation for this behaviour is given which employs capillary theory for water entry, and interactions among the size, number and morphology of water-conducting macropores during the infiltration process.