A review of research on seedbed preparation for small grains in Sweden

Seedbed preparation research in Sweden over the past 35 years is reviewed. In Swedish farming, spring sown small grains are the dominant crop, but their establishment is often problematic. The spring is the driest season and this may cause poor crop emergence, particularly in clay and clay loam soils, where the seedbed often becomes coarse and non-uniform and dries out quickly. In silty soils, the major problem is surface layer hardening that hampers seedling emergence. Seedbed problems have attracted considerable research interest. A method to characterize seedbed properties based on frame sampling is presented. A survey of seedbeds in farm fields showed that the water content at traditional spring sowing of small grains (as soon as the soils are dry enough for harrowing) is usually below wilting point to a depth of 3 cm in soils with >25% clay, but in coarse-textured soils, there is usually plant available water up to the soil surface. The function of seedbeds was investigated by establishing seedbeds with predetermined properties and sowing depths in shallow plastic boxes. Under dry weather conditions, good emergence of small grain crops could always be achieved without irrigation, provided the seed was placed directly onto a firm seedbed base with a water content at least 0.05 g g−1 greater than that at a matric tension of 1500 kPa and was covered by a 4 cm deep seedbed with >50% aggregates <5 mm. The risk of poor emergence due to surface layer hardening depended much more on the sowing depth than on the aggregate sizes of the seedbed. Several series of field trials are also summarized. In trials on silty soils, a fine seedbed increased both number of plants and crop yield by 5% as compared to a coarse seedbed. In clay and clay loam soils, natural factors, particularly previous freezing and thawing, affected seedbed characteristics more than the choice of harrows and their adjustment or the number of harrowings. In most soils, rolling after sowing improved final emergence of cereals by 4% and grain yield by 2%. Very early sowing in wet soils, without any preceding seedbed preparation, increased crop yield by about 20% in sandy soils, and was often advantageous even in clay soils. On the basis of our experimental results, the goals of seedbed preparation for cereals are specified by means of seedbed models.