EFFECTS OF AGE OF TEA PLANTATIONS ON DISTRIBUTION OF EXCHANGEABLE BASE CATIONS IN SOIL AGGREGATES
Through field investigation and laboratory analysis,effects of age of tea plantations on distribution of exchangeable base cations in soil aggregates were studied.Results show that (1) content of soil exchangeable K+ increased first and then decreased with increasing particle size of the soil aggregates.The distribution of exchangeable Mg2 + was relatively even in soil aggregates of all particle sizes,and contents of exchangeable Na + and Ca2 + and total exchangeable bases (TEB) increased with decreasing particle size of the soil aggregates.Average contents of the base cations in soil aggregates regardless of particle size show an order of Ca2 + ＞ Mg2 + ＞ K + ＞ Na +.(2) Along with rising age of the tea plantations contents of exchangeable K + and Na + presented a decreasing trend in soil aggregates of all particle sizes.However,contents of exchangeable Ca2+ and Mg2+ and TEB displayed a rising-and-falling trend,and higher values were found in tea plantations,23 and 31 years of age.The changes were more evident in the 0 ～ 20 cm soil layer than in the 20 ～ 40 cm soil layer.(3) In tea plantations regardless of age,the content ratio of (K + + Na +)/(Ca2 + + Mg2 +) increased first and then decreased with decreasing particle size of the soil aggregates and content of soil aggregates showed a decreasing-increasingdecreasing trend with decreasing particle size.Along with rising age of the tea plantations,the content ratios of (K ++ Na+)/(Ca2+ + Mg2+) in soil aggregates of all particle sizes presented a decreasing-first-and-then-increasing trend and were particularly lower in tea plantations 23 and 31 years of age,which was contrary to the variation of the content of ＞5 mm aggregates,and more evident in the 0 ～ 20 cm soil layer.Soil aggregates,different in particle size,differed sharply in exchangeable base cations retaining capacity and supplying capacity.Contents of exchangeable K + and Na + decreased year by year in aggregates of all particle sizes,and contents of exchangeable Ca2 + and Mg2 + were found to be higher in tea plantations,23 and 31 years of age,and declined somewhat afterwards.Therefore,in management of tea gardens,it is essential to adopt balanced application of nitrogen and potassium fertilizers,and in tea plantations older than 23 in age,to use organic manure in addition,enhance soil and water conservation and prevent serious soil acidification,so as to reduce leaching loss of exchangeable Ca2+ and Mg2+.
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