Influence of time of tillage on soil physical attributes in potato rotations in Prince Edward Island

In Atlantic Canada, lack of soil cover over the cool season due to conventional primary tillage in the fall, in potato rotations, leaves the soil vulnerable to redistribution processes. The suitability of shifting primary mouldboard plough tillage operations from the fall to the spring in the potato (Solanum tuberosum L.) phase of a 3-year rotation (spring barley (Hordeum vulgare L.)-red clover (Trifolium pratense L.)-potato, or replacing fall mouldboard with fall chisel ploughing, was assessed over a 3-year period on Charlottetown fine sandy loam, an Orthic Podzol. A suite of soil physical attributes was used to assess the influence of primary tillage on the degree of soil loosening, permeability, and macro-structure. Potato yield and quality were also determined. Although, mouldboard ploughing provided an additional 2-10 cm of loose (i.e. penetration resistance <1.5 MPa) soil at the lower depth of the tillage zone, compared to chisel ploughing, there were no differences in soil permeability as measured by bromide movement. Soil macro-structure, or clod size, in the potato ridge just prior to harvest reflected the degree of secondary tillage rather than the influence of primary tillage. Clod size distribution in the potato ridge was not a problem for harvesting operations as clods did not exceed 20 mm in diameter. Soil permeability at the base of the potato ridge, as assessed by oxygen diffusion rate (>55 mu g m(-2) s(-1)), air permeability, and macropore continuity (quotient of air permeability and macropore volume, >100 mu m(2)), and soil shear strength (<22 kPa) were not limiting for root growth. However soil pore space, as reflected by bulk density (>1.25 Mg m(-3)) and macropore volume (<12%) would pose a soil aeration limitation in this soil-type at the base of the ridge under wet soil conditions. Potato total yield and marketable yield were not influenced by differences in primary tillage over the 3-year period. Use of spring primary tillage and replacement of the mouldboard with a chisel plough, within the potato phase of a 3-year rotation, caused little change in soil physical quality compared to the conventional tillage system and appears to be a suitable conservation tillage technique for sandy loam soils in the climate of Atlantic Canada. (C) 1998 Elsevier Science B.V. All rights reserved.