Responses of Leymus arenarius to nutrients: improvement of seed production and seedling establishment for land reclamation.
Iceland has vast areas of mobile sand resulting from volcanic glacier bursts and erosion. Seeds of the coastal, dune-building grass Leymus arenarius are harvested from natural stands for use in extensive land reclamation programmes. The economic use of fertilizer treatments in managing the production of seeds, and to facilitate the establishment and survival of seedlings was investigated. Seed yield could be increased dramatically in coastal dunes by the application of N fertilizers, mainly as a result of increased flowering-spike density. Little short-term advantage accrued from additions of P or K. Additions of N (rapid-release formulations) at 50-100 kg/ha were considered highly cost-effective in providing the current production from a much smaller area of dunes or in increasing seed production. Other consequences would be to minimize the environmental impact of harvesting and to allow more focused management of the seed resource. If periodic applications of P and K were necessary to maintain yield, these would be economically justifiable. Establishment of seedlings on volcanic, sandy barrens over the first 2 seasons from sowing was improved by the application of slow-release fertilizers but rapid-release formulations applied annually produced a similar tiller density and biomass after 4 years more economically. Untreated control populations became extinct over the same period. A sand-culture experiment indicated that plants severely deprived of P allocated more dry mass to roots and rhizomes, and those deprived of K allocated more to aboveground parts. These responses could be manipulated to improve establishment in slowly and rapidly accreting environments, respectively. The seed production of moribund, late-successional stands was not rejuvenated by fertilizer application.