Soil and residue management effects on arable cropping conditions and nitrous oxide ̄uxes under controlled traf®c in Scotland 1. Soil and crop responses

Soil compaction can affect crop growth and greenhouse gas emission and information is required of how both these aspects are affected by compaction intensity and weather. In this paper we describe treatments of compaction intensity and their effects on soil physical conditions and crop growth in loam to sandy loam cambisol soils. Soil conditions and crop performance were measured over three seasons in a ®eld experiment on soil compacted by wheels on freshly ploughed seedbeds. Ploughing buried the chopped residues of the previous crop. After ploughing, traf®c was controlled such that the experimental plots received wheel traf®c only as treatments. The overall objective was to discover how the intensity and distribution of soil compaction just before sowing in ̄uenced crop performance, soil conditions and emissions of nitrous oxide. Compaction treatments were zero, light compaction by roller (up to 1 Mg mÿ1) and heavy compaction by loaded tractor, (up to 4.2 Mg). The experiment was located at Boghall, near Edinburgh (860 mm average annual rainfall) for the ®rst two seasons under spring and winter barley (Hordeum vulgare L.) and in a drier area at North Berwick (610 mm average annual rainfall) for the third season under winter oil-seed rape (Brassica napus L.). Heavy compaction in dry soil conditions had little effect on crop growth. However, in wet conditions heavy compaction reduced air porosity, air permeability and gas diffusivity, increased cone resistance and limited winter barley growth and grain yield. Heavy compaction in wet conditions reduced winter barley yields to 7.1 Mg haÿ1, in comparison to 8.8 Mg haÿ1 in the zero compaction treatment. The compaction status of the top 15 cm of soil seemed to be particularly important. Loosening of the top 10 cm of soil immediately after heavy compaction restored soil conditions for crop growth. However, zero seed bed compaction gave patchy and uneven crop emergence in dry conditions. Both zero and light compaction to a target depth of 10 cm gave similar crop productivity. Maintenance of a correct compaction level near the soil surface is particularly important for establishment and overwintering of barley and oil seed rape. # 1999 Elsevier Science B.V. All rights reserved.