Säkrare etablering av våroljeväxter med grund bearbetning på våren

Abstract: Spring oilseed rape is an important break crop in cereal dominated crop rotations in Mälardalen. Also, it is one of few good preceding crops to winter wheat. Establishment of spring oilseed rape is perhaps the most critical moment in arable cropping, especially under dry conditions on clay soils. In conventional systems, drying of soil during spring often makes it difficult to obtain enough soil moisture within the seedbed base for small-seeded species which are to be planted shallow. For saving as much soil moisture as possible within the soil for germination of spring oil seed rape, an alternative to using conventional machinery with plowing, harrowing and sowing, is to leave the soil unaltered during fall and instead use shallow cultivation in spring. The aim of this work was to study different strategies for establishment of spring oilseed rape to determine if reduced/shallow tillage can increase cropping reliability for this crop. The study was conducted on three clay soils, differing in clay content, outside Uppsala. The field experiments had a two factorial randomized block design with four replicates. Four tillage methods, where ploughing in autumn was compared with reduced tillage using disc harrows conducted in autumn or in spring or in autumn and spring were combined with two dates of sowing, early and late. Furthermore, an on farm study was conducted in Vassunda outside Uppsala where the farmer is practicing reduced tillage in the spring to spring oilseed rape. Seedbed properties such as surface smoothness, seedbeds depth and aggregate size distribution within the seedbed were characterized. Furthermore, gravimetric soil water content in the seedbed base at sowing and volumetric soil water content in the seedbed base at sowing and after emergence was determined. After emergence, the number of plants was counted at two occasions. A grading of the damage of the crop made by flea beetles (phyllotreta) was carried out. Yield data were collected from field trials as well as from the farmer in Vassunda. Results showed that cropping reliability for spring oil seed rape was at least as high for reduced tillage as for conventional tillage, using a mouldboard plough in autumn. The conditions for cropping of oil seed rape in the area were unusually favorable during the year that the field trial was conducted. Yields were therefore high in all tillage methods and no significant differences were found. Autumn plowing with conventional seedbed preparation resulted in a high proportion of fine soil within the seedbed and high plant emergence. At the same time it resulted in the driest seedbed bottom and the highest infestation of flea beetles. Shallow tillage only in spring resulted in a rough structure of the seedbed with a high proportion of large aggregates and low plant emergence, but had highest soil moisture content in the seedbed bottom and also lowest infestation of beetles. No correlation between plant emergence and crop yield was found. Early sowing gave a significantly higher yield than late sowing. The farmer in Vassunda was successful and obtained a satisfactory tillage outcome with a high proportion of fine soil (aggregates <5 mm in diameter) and a good plant emergence. The field experiment shows that reduced tillage can be a safe option for spring oilseed crops as well as a way to reduce the cost for cultivation.