Open access publications in the SLU publication database

Abstract

This doctoral thesis examines if water dynamics before and during seedling emergence after autumn and summer direct seeding can be controlled in Scots pine (Pinus sylvestris L.) seeds by hydrophobic polymer coating and hydrophilic (hydrogels) polymer packages. A method was created by using scanning electron microscopy (SEM) to evaluate the quality of the polymer seed coating. Differential scanning calorimetry (DSC) and germination tests indicated that the critical moisture content of Scots pine seeds under freezing conditions was between 15%-20%. After autumn seeding, the coating (Ethocel™ polymer) thickness that resulted in the highest seedling emergence was 2.0% weight gain. On three seeding sites this treatment resulted in seedling emergence of 33.7%, 30.0%, and 14.1%, whereas the uncoated seeds had values of only 12.3%, 0.0%, and 1.0%. Summer direct seeding was done with three different scarification techniques - organic removal, huminmix, and mounding. Seedling emergence was compared within each scarification type for different initial seed moistures (dry and invigorated 30% moisture content, not re-dried), soil preparations (2-cm indentation, 2-cm wick and, 6-cm wick), and polymer (hydrogel Ac-Di-Sol®) preparations (powder, gel, and gel/peat). The highest seedling emergence was associated with invigorated seeds prepared with gel/peat package and a 6-cm wick for organic removal (32.5%), huminmix (30.7%) and mounding (18.8%). Invigorated seeds, regardless of treatment, had seedling emergence higher than dry seeds, and control values of dry seeds were significantly lower than for invigorated seeds. The delay of water uptake (probably in combination with sufficient snow cover insulation during winter months) made autumn direct seeding of coated seeds successful. The use of hydrogels, seed invigoration (not re-dried seeds), and soil preparation/wicks improved seedling emergence after summer direct seeding in dry conditions.