Effect of nitrogen and phosphorus availability on the emergence, growth and over-wintering of Rumex crispus and Rumex obtusifolius

Rumex crispus and R. obtusifolius are known to be nitrophilous but it is not known whether either or both species require a high N supply at all developmental stages. Furthermore, it is not clear whether both species require a high P supply, attain flowering in the seeding year, or have similar levels of winter resistance. The effect of nutrient availability on the emergence, growth and over-wintering of both Rumex species was investigated in a pot experiment (ten N, P and K fertilizer treatments) in Prague, Czech Republic. In both species, emergence of seedlings was negatively affected by very high N, but positively affected by increased P availability in the soil. No effect of K supply on the emergence, or subsequent growth, was recorded. High flowering in the seeding season and high winter mortality of R. obtusifolius contrasted with no flowering and no mortality of R. crispus. Over-wintering was not markedly affected by N, P or K supply. Both Rumex species are sensitive to a very high N supply in early developmental stages but tend to require a high N supply from the fully developed rosette-stage onwards. In addition to high N requirements during stem growth, flowering and seed ripening, both species also require a high P supply. At least some Central European populations of R. crispus, in contrast to R. obtusifolius, do not flower in the seeding year. In Central Europe, the frequently reported high field winter mortality of R. obtusifolius can be caused by its low frost resistance.