Evaluation of shallow tillage for spring cereals on a fine sandy loam. 2. Soil physical, chemical and biological properties

Abstract

Changes in the soil condition were determined over a 4-year period, to assess the use of shallow tillage for the low-input production of spring cereals in Prince Edward Island. The soil was a Charlottetown fine sandy loam (Orthic Podzol) which has a low resistance to compaction. Shallow tillage (rotary harrow, disc harrow) was conducted to the 10 cm soil depth and compared with mouldboard ploughing (20 cm) and direct-drilling. Shallow tillage caused excessive compaction in the middle portion of the Ap horizon (8–16 cm) as characterized by reduced macroporosity (<12%, v/v) and increased relative compaction (>85%). Penetrometer resistance measurements indicated that both shallow tillage and direct-drilling reduced the depth of loose soil (<1.5 MPa) to 10–15 cm, compared with 20–25 cm under ploughing. Shallow tillage improved the size distribution of macro-aggregates and increased the stability of 1–9 mm aggregates at the soil surface (0–3 cm). Differences in placement and incorporation of crop residues and amendments caused a redistribution of organic matter, microbial biomass, and extractable P and Ca within the Ap horizon. An acidic, lower Ap horizon developed over time in the shallow-tillage system. The tillage requirement for acidic, fine sandy loams would necessitate a periodic increase in tillage depth for long-term shallow-tillage systems to remove middle Ap horizon compaction and to provide deeper soil mixing of lime amendments to neutralize soil acidity.