Characterisation of water transmission properties in tilled and untilled soils using tension infiltrometers

Abstract

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. It was concluded that the TI technique is effective for characterising differences in K 0 and R 0 between NT and MP continuous maize production systems.