Interactions of nitrogen and phosphorus in plant nutrition - Analysis of a 60-years old field experiment

Abstract Background and aims The aims are to determine to which extent different plant species increase nitrogen (N) acquisition in response to phosphorus (P) addition and P acquisition in response to N addition as well as to analyze resulting nutrient limitations. Methods The field experiment is replicated at ten sites in Sweden and comprises three fertilization regimes (low, medium, and high) each consisting of a control and a N, P, and NP treatment. Yields as well as N and P contents of the yields of four species (winter wheat, spring barley, oat, and sugar beet) were analyzed over 60 years. Results The relative increase in yield P in response to N fertilization was larger than the relative increase in yield N in response to P fertilization for three species. Synergistic NP co-limitation was observed for all species at some sites. The synergistic growth effect in response to NP addition occurred at more sites at high than at low fertilization. At one nutrient-poor site, all species in all fertilization regimes were (synergistically) NP co-limited. Sugar beet was (synergistically) NP co-limited at all sites in all fertilization regimes. Conclusion Species differed in nutrient acquisition, but most species used added N more effectively to acquire P than they used added P to acquire N. Synergistic NP co-limitation was observed for all plant species at some sites, and it increased with fertilization rate, which is likely due to the limits to which plants can use N to acquire P and P to acquire N.