Effect Of Nitrogen Compound Additions On Soil Exchangeable Base Cations And Acid Buffering Capacity In Meadow Grassland

Nitrogen?N?is an important factor that limiting the productivity of terrestrial ecosystems,and has an important influence on the biodiversity and stability of the ecosystems.The increased nitrogen input results in soil acidification,exhaust of soil exchangeable base cations and decrease of soil acid buffering capacity.However,the effects of different N compound additions on soil acidification in grassland are yet unclear.Based on the N compound addition experiment in Erguna Forest-Steppe Transition Ecotone Research Station,Institute of Applied Ecology,Chinese Academy of Sciences,this paper studied the effects of different N compound additions on exchangeable base cations and acid buffering capacity in the topsoil?0-20 cm?in a meadow grassland in North China.The experiment included five N compounds,i.e.,ammonium carbonate?NH₄HCO₃?,ammonium nitrate?NH₄NO₃?,ammonium sulfate?NH₄?₂SO₄),urea?CO?NH₂?₂?,and slow-released urea,respectively;six N addition rates,i.e.,0,2,5,10,20,and 50 g N m^-2 a^-1,respectively;and two management patterns,i.e.,mowing and unmowing.Totally there were sixty treatments,eight replications and 480 plots.The results obtained are as follows:1.With the increasing nitrogen addition rates,soil pH and soil acid buffering capacity?Acid BC?were significantly decreased,indicating the addition of N compounds accelerating soil acidification of the meadow grassland;soil electric conductivity?EC?was significantly increased,indicating the accumulation of soil soluble salts in the grassland with N additions.The effects on soil pH,acid BC and EC were significantly different among N compounds.Of the five N compounds,the soil acidifying effects from strong to weak are in the sequence of ammonium sulfate,ammonium nitrate,urea,slow-released urea,and ammonium carbonate.Moving treatment had no significant effects on soil pH,EC and soil Acid BC.2.Nitrogen addition rates had significantly effects on soil exchangeable calcium(Ca²⁺),magnesium(Mg²⁺),potassium?K⁺?,sodium?Na⁺?,and the sum of exchangeable base cations?SEB?.With the increasing nitrogen addition rates,soil exchangeable Ca²⁺and Mg²⁺were significantly decreased,while exchangeable K⁺was significantly increased.Nitrogen compound types had significant effects on soil exchangeable Ca²⁺,Mg²⁺,K⁺and SEB,but had no influence on exchangeable Na⁺.Mowing treatment had significant effects in soil exchangeable Ca²⁺and SEB,but had no effects in exchangeable Mg²⁺,K⁺,or Na⁺.3.Nitrogen addition rates had no significant effect on soil exchangeable Ca²⁺/Mg²⁺,Ca²⁺/SEB,Mg²⁺/SEB,and Na⁺/SEB.With the increasing nitrogen addition rates,soil exchangeable Ca²⁺/K⁺,and(Ca²⁺+Mg²⁺)/?K⁺+Na⁺?decreased,but K⁺/SEB,and K⁺/Na⁺increased,indicating the decrease of Ca and Mg availability,but the increase of K availability.Nitrogen compound types had only significantly influenced K⁺/Na⁺,and mowing treatment only affected Ca²⁺/Mg²⁺and Mg²⁺/SEB.4.In both mowing and unmowing treatments,soil pH was positively correlated with soil exchangeable Ca²⁺,Mg²⁺,Na⁺,and SEB,but negatively with soil exchangeable K⁺.Soil EC was negatively correlated with exchangeable Ca²⁺,Mg²⁺,and SEB,but not correlated with exchangeable K⁺.Soil EC was not correlated with exchangeable Na⁺under unmowing treatment,but negatively exchangeable Na⁺under mowing treatment.In both mowing and unmowing treatments,soil acid-neutralizing capacity?ANC?was positively correlated with exchangeable Ca²⁺,Mg²⁺,and SEB,but not correlated with exchangeable K⁺or Na⁺,indicating that soil ANC is mainly influenced by exchangeable Ca²⁺,Mg²⁺,and SEB in the meadow grassland soils.