Polymer coated turnip rape seed did not facilitate early broadcast sowing under Finnish growing conditions

An alternative sowing time for summer turnip rape (Brassica rapa L. var. oleifera subvar. annua) and canola rape (Brassica napus L. var. oleifera subvar. annua) was investigated under northern European growing conditions, where the growing season is very short and seedling establishment in spring is difficult. Using a method termed carrier technology, seeds of spring canola were coated with polymer and sown in winter or early spring. Two types of polymer were tested: water-impervious Poligen (R) WE3 (polyethylene wax at five rates depending on experiment) and water-soluble, freeze sensitive Extender (R) (GrowTech at 3% of seed weight). Four separate field experiments at two locations (Jokioinen, 60 degrees 81'N and Mietoinen, 60 degrees 38'N) and two laboratory experiments were carried out in 2002-2004. Early sowing times were used in combination with autumn control of weeds using non-selective herbicides and broadcast sowing onto cereal stubble to promote cost-efficiency. Such sowing method failed to produce even plant stands, as only few seedlings emerged. The polymer coatings were successful and the water-soluble, freeze sensitive polymer designed to allow an alternative sowing time performed well in laboratory tests. Large numbers of early sown coated and control seeds remained viable until the end of spring. Under field conditions germination or seedling establishment failed probably due to poor seed-to-soil contact. Moreover, unfavourable winter and spring conditions likely resulted in lack of synchrony between adequate temperature and water availability needed for seed imbibition and germination.