Long-term soil nutrient dynamics and lateral nutrient movement in fertilized and unfertilized red pine plantations

In this study, we use arepeated-measures analysis to test thehypothesis that soil fertility underpotassium-limited red pine (Pinusresinosa Ait.) stands at the Charles LathropPack Demonstration Forest in Warrensburg, NewYork is increasing toward a steady state thatwas artificially induced in fertilized standsby K-fertilization over 50 years ago. Wemeasured soil K by horizon and added new datato a 53-year database. We examine onemechanism that explains the higher rate of Kaccumulation in unfertilized stands comparedwith fertilized – lateral movement offertilizer K from treated plots to untreated –using the rubidium/potassium reverse tracermethod. Over the past five decades, soil Kconcentrations under both fertilized andunfertilized red pine have increasedsignificantly. The trends under fertilized andunfertilized plots demonstrate the gradualconvergence of soil K under unfertilized plotstoward concentrations in fertilized plots. Five decades after fertilization, treated soilsstill contain greater concentrations ofexchangeable K and lower bulk densities thanunfertilized plots. Analysis of Rb/K ratios inthe forest floor of fertilized and unfertilizedplots confirms the hypothesis that lateraltransport of surface broadcast fertilizer,applied over 50 years ago, extendsapproximately 11–16 m from the edges offertilized plots. The four unfertilized plotsclosest to fertilized plots have beensignificantly affected by inputs of fertilizerK, while the remaining five plots arerelatively unimpacted. Approximately 36% ofthe K in fertilized plots, and 23% of the K inunfertilized plots affected by fertilizermigration were derived directly from thefertilizer applied 5 decades ago, demonstratingthe highly conservative nature of mineralnutrient cycling in aggrading forests.