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 con ventional primary tillage in the fall, in potato rotations, leaves the soil vulnerable to redistribution processes. The suitability of shift ing 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 Or thic Podzol. A suite of soil physical attributes was used to assess th e influence of primary tillage on the degree of soil loosening, permea bility, and macro-structure. Potato yield and quality were also determ ined. 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 diffe rences in soil permeability as measured by bromide movement. Soil macr o-structure, or clod size, in the potato ridge just prior to harvest r eflected 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 dia meter. 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 volu me, >100 mu m(2)), and soil shear strength (<22 kPa) were not limiting for root growth. However soil pore space, as reflected by bulk densit y (>1.25 Mg m(-3)) and macropore volume (<12%) would pose a soil aerat ion limitation in this soil-type at the base of the ridge under wet so il conditions. Potato total yield and marketable yield were not influe nced 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 c hange in soil physical quality compared to the conventional tillage sy stem and appears to be a suitable conservation tillage technique for s andy loam soils in the climate of Atlantic Canada. (C) 1998 Elsevier S cience B.V. All rights reserved.