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

Tension infiltrometer (TI) measurements from a silty clay loam soil (W inchester, Ont.), a sandy soil (Hancock, WI), and a silt loam soil (Ro semount, MN) were used to: (i) characterise near-saturated hydraulic c onductivity (K-0) and flow-weighted mean radius of soil macropores (R( 0)); (ii) distinguish differences in these water transmission properti es between no-till (NT) and mouldboard plough (MP) continuous maize (Z ea 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 membrane s were increased incrementally from the minimum values (P-0 = -10 cm o r -15 cm) to the maximum value (P-0 = 0 cm). This indicates that subst antial networks of water-conducting soil macropores exist in continuou s maize production systems, regardless of soil texture or tillage trea tment. 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 consiste ntly 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 probab ly 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 beh aviour is given which employs capillary theory for water entry, and in teractions among the size, number and morphology of water-conducting m acropores during the infiltration process.