The effect of straw management and reduced tillage on soil properties and crop yields of spring-sown cereals on two loam soils in Norway

Straw residues on the soil surface are considered to be a problem when a reduced tillage system is used. Therefore, shallow tillage and direct drilling in combination with straw residues management were investigated in two field experiments in southeastern Norway. The experiments were established in the autumn of 1990 on a loam (Gleyic Phaeozem) and a silty clay loam (Gleyic Luvisol) soil. Shallow tillage was conducted as autumn and/or spring harrowing. Direct drilling was carried out using disc and tine/wing coulters. The straw management included chopping, burning, removing, shallow incorporation (2 cm) and deep incorporation (8 cm) of annual straw yield (normal amount) in addition to chopping of double the amount of annual straw yield. The crops were spring barley (Hordeum vulgare L.), spring oats (Avena sativa L.) and spring wheat (Triticum aestivum L.). Normal and double amounts of chopped straw residues, on the soil surface increased the mean grain yields during the experimental period (1991-1996) by 0.290 Mg ha(-1) compared with the mean of the other straw treatments. In 1995, a year with far more rainfall than the long-term means for June, a grain yield reduction of 0.336 Mg ha(-1) was measured on plots with normal and double the amount of chopped straw residues compared with the mean of the other straw treatments. The reduction of evaporation because of a straw cover was probably the most important reason for the increased grain yields in dry years. Straw treatment did not influence total porosity, bulk density or pore size distribution in the 2-7 cm soil depth during the first five years. Aggregate stability increased by 0.07 kg kg(-1), the fraction of coarse aggregates (>0 mm) increased by 0.07 kg kg(-1) and the fraction of fine aggregates (<0.6 mm) decreased by 0.08 kg kg(-1) when normal and double the amount of chopped straw residues were left on the surface compared with the mean of the other straw treatments. This study indicated that shallow tillage and direct drilling in combination with a high amount (6-8 Mg ha(-1)) of chopped straw can be used for spring-sawn cereals an loamy soils in a temperate humid climate as in southeastern Norway, without any significant reduction in crop production. (C) 1999 Elsevier Science B.V. All rights reserved.