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Characterising field emergence in cultivated herbaceous vegetation

Final Activity Report Summary - FIELD EMERGENCE (Characterising field emergence in cultivated herbaceous vegetation)

The study discussed in this document was designed to further co-operation between the Department of Landscape, University of Sheffield and Jelitto Seeds in the development of seed mixes to create more sustainable, naturalistic herbaceous vegetation in the public greenspace of European cities. Over the past 15 years Professor James Hitchmough in the Department of Landscape has pioneered the establishment of designed herbaceous plant communities by sowing seed in situ. Jelitto Seeds are the leading company in the world in developing and marketing seed of herbaceous perennials and grasses for the nursery industry. In achieving this overall goal, the study hoped to further understanding of seed germination and dormancy and to improve reliability of seed mixes as a product, providing much greater control over the subsequent composition and development of sown, designed plant communities. The project is discussed around the three phases of research stated in the "Description of Work".

Phase 1 Investigate seedling emergence in the laboratory, pot trials and in the field
This phase investigated how factors such as seed weight, plant habitat, degree of seed dormancy interact with regional climate, the nature of the sowing mulches used, and irrigation ultimately determine typical field emergence. In total 81 species of herbaceous plant species were investigated in this phase, sown into three different environments; i) filter papers in the Jelitto Seeds seed testing laboratory, 9cm pots in the open air, and "beds" in the open air. The basis hypotheses were as follows:
i) Germination in the lab over-estimates field emergence of species in the field
ii) Emergence in sowing mulch substrate in pots is similar to emergence in the same sowing mulch in commercial sowings in the field

Three substrates were used in the outdoor pot and bed treatments: composted green waste (100%); coarse sand (100%), and an intermediate (composted green waste:coarse sand, as a 50:50 mix). These substrates were used as 50mm layers of mineral or organic material that does not contain an extensive weed seed bank, spread on the soil surface to suppress the weed seeds present.
The sowing mulches in pot and bed treatments were also subject to a gradient of irrigation regimes, as soil moisture stress at germination is a dominant determinant of field emergence. Irrigation treatments used were nil, 25mm/week, 25mm twice a week. For each substrate x irrigation treatment combination 30 seed of each species were sown, with five replicates of all combinations. The experiments were conducted as large randomised block designs in Sheffield and near Hannover in Germany.

Phase 2 Use pot screening to characterise field emergence of up to 1000 species
The aim of this work was to generate typical field emergence data for a large number of species drawn from the Jelitto Catalogue that have high potential for sowing in situ to create naturalistic herbaceous plant communities in urban landscapes. 741 species were tested in total. Phase 1 of the study had shown that sowing in pots provided a close approximation to field emergence in commercial practice (the "bed" treatment). As a result seeds were sown in 9cm pots using a 50:50 mix of composted green waste and coarse sand. Pots were subjected to two watering treatments; watered once a week, and watered twice a week. Seedlings per pot were counted at two occasions, and expressed as field emergence. The effect of watering frequency was most marked for the summer sown non-dormant species, i.e. those that had to germinate during times of greatest potential soil moisture stress.

Phase 3: To test the reliability of screening protocols in practice through field scale sowing experiments involving formulated seed mixes.
In order to maximise the time available to assess the resulting sown plant communities, and to maximise value to the commercial partner, this phase of the work commenced in the second year in Germany, and continued into the third year of the study.