BASIC CATION SATURATION RATIO THEORY APPLIED TO SAND-BASED PUTTING GREENS

摘要

The basic cation saturation ratio theory of soil test interpretation states that calcium (Ca),magnesium (Mg),and potassium (K) should be present on the cation exchange sites of the soil in the following percentages,65 – 85%,6 – 12% and 1 – 5%,respectively.Golf course putting greens are often constructed utilizing a sand-based rootzone.Since sands generally have a low cation exchange capacity (CEC),it is possible that the Ca,Mg,and K cations can occupy the correct ratios within the rootzone yet fail to support optimal growth.Also,the validity of these cation ratios has not been thoroughly evaluated for creeping bentgrass on low CEC soil media.The objective of this research was to evaluate the BCSR theory for sand-based greens.Twenty-eight cation treatments of widely varying cation ratios were applied to 'Penncross' creeping bentgrass (Agrostis stolonifera L.) established on either calcareous or silica sand.Creeping bentgrass tolerated a wide range of applied cation ratios,as no differences in quality or growth rate were observed among the 28 treatments.Samples from the silica sand pots had high K saturation percentages,>28%,but leaf and soil extractable K concentrations were very low,<21 g?kg-1 and <1.6 mg?kg-1,respectively.The Ca:K ratios of silica sand ranged from 1:1 to 2:1,whereas; according to the BCSR theory,they should be 13:1 and a Ca application would be recommended to correct the ratio.However,leaf Ca concentrations from grass grown on silica sand were high (12 g?kg-1) and leaf K concentrations were low (8.7 g?kg-1).Dissolution of CaCO3 from calcareous sand samples resulted in Ca saturations percentages greater than 95%.Additionally,the silica sand samples had such low CEC that calculated cation saturation percentages and ratios gave misleading results.Using the BCSR theory on low CEC sands results in widely varying cation saturation ratios that may lead to erroneous interpretations of soil test results.It is recommended that the results of BCSR interpretation not be used as the final determining factor in developing fertility systems for sand-based golf course greens.