Evaluation of Rapid Methods for Determining Lime Requirement Using East Texas Soils

1. Evaluation of Rapid Methods for Determining Lime Requirement Using East Texas Soils Leon Young & Henry Dlamini, Stephen F. Austin State University, Nacogdoches, TX • INTRODUCTION • The Adams-Evans method (Adams & Evans, 1962) has been used for many years as the buffer pH method for determining Lime Requirement (LR) of soils in the Southeastern Region of the U.S. The buffer contains paranitrophenol which is a hazardous material requiring expensive disposal measures. • Two modified Adams-Evans buffer methods have been proposed and are currently being used by Extension labs in the region. The Modified Adams-Evans developed by Huluka (2005 & 2007) substitutes monobasic potassium phosphate for the p-nitrophenol and changes the concentration of KOH and H2BO3. The Moore-Sikora ( Moore & Sikora, 2007) method uses MES (N-morpholino ethanesulfonic acid hydrate) and MOPS (3- N- Morpholino, propanesulfonic acid) to replace the p-nitrophenol. In addition, Kissel et al. (2007) have implemented a rapid single addition titration combined with 0.01 M CaCl2 “salt pH” method for determining lime requirement. • OBEJECTIVES • Evaluate different LR methods • Evaluate effects of 1:1 and 1:2 water to soil ratios • Evaluate effects of using 0.01 M CaCl2 “salt pH” • Select best method for East Texas Soils • METHODS • Selected 51 soils from a set of 64 soils collected from the region and used in previous studies of LR • Measured soil pH using 1:1 and 1:2 soil to water ratios with and without 0.01 M CaCl2 • Determined LR using a series of Ca(OH)2 incubations on each sample • Determined Standard Lime Requirement (SLR) using Ca(OH)2 incubation data plus Ca(OH)2 titration data from the previous studies • Determined LR using the following rapid methods: • Original Adams-Evans Buffer (AE) • Modified Adams-Evans (MAE) • Moore-Sikora (M-S) • University of Georgia single addition titration (UGA-ST) • All three Adams-Evans methods use the relationships and equations developed by Adams and Evans (1962). Lime Requirements (LR) are expressed in U.S. tons per acre of ECCE (Effective Calcium Carbonate Equivalent) which is pure calcium carbonate that passes a 60 mesh screen. Methods are compared to a Standard Lime Requirement (SLR) which is the mean lime requirement of the titrations and incubations shown in the following graph. The mean SLR for the 51 samples is 0.62 tons ECCE per acre. • The MAE had an R2 value of 0.67 and over estimated LR approximately 500 kg ha-1. • The Moore-Sikora requires the use of two expensive chemicals. A cost comparison using current prices for MOPS and MES, current lab procedure at the SFASU Soil, Plant and Water Analysis Laboratory and current disposal charges for paranitrophenol. The results indicate that the MOPS plus MES cost about $117 per 1000 soil samples while disposal of paranitrophenol costs between $63 and $97 per 1000 samples. The Material Safety Data Sheet (MSDS) from Mallinckrodt Baker (2009) indicates that the half life of the paranitrophenol is less than one day in soil. With further study, incubation of the soil with A-E buffer may provide an even less expensive method of disposal. • CONCLUSION • Based on this work, the original Adams-Evans method is superior to the other methods tested in predicting LR on East Texas Soils. In addition, the cost of disposing of the paranitrophenol is somewhat less than using the expensive chemical in the Moore-Sikora method. • LITERATURE • Adams, F. and C.E. Evans. 1962. A rapid method for measuring lime requirement of yellow podzolic soils. Soil Sci. Soc. of Amer. J. 36:355-337. • Huluka, G. 2005. A modification to the Adams-Evans soil buffer determination solution. Comm. in Soil and Plant Anal. 36:2005-2014. • Huluka, G. 2007. A modification to the Adams-Evans soil buffer solution. http://www.clemson.edu/agsrvlb/sera6/publications1.htm • Kissel, D.E., R.A. Isaac, R. Hitchkock,. L.S. Sonon, and P.V. Vendrell. 2007. Implementation of soil lime requirement by a single addition titration method. Soil Sci. and Pl. Anal J. 38:1341-1352. • Mallinckrodt Baker, Inc., 2009. Material Safety Data Sheet for p-nitrophenol, CAS No.:100-02-07,5 May 2009. http://www.jtbaker.com/msds/englishhtml/n6040.htm • Moore, K.P. and F.J. Sikora. 2007. Replacing Adams-Evans with Moore-Sikora buffer for determining lime requirement of soil http://www.clemson.edu/agsrvlb/sera6/publications1.htm • Thompson, J. 2008. Reaction equilibration from single-addition base titration for lime requirement. Personal communication, M.S. Thesis, University of Georgia. The UGA-ST method uses a basic equation developed to calculate LR and abbreviated as UGA-F1. A second equation, abbreviated as UGA-F2, adjusts for the difference in LR between the rapid addition of Ca(OH)2 and the LR determined by incubation (Thompson, 2008). RESULTS • Numerous combinations 1:1 and 1:2 soil to water ratios, with and without the use of salt pH were used with each method. A soil pH for use in the method formula was obtained by adding 0.6 pH units to the salt pH. Use of 1:2 ratio pH and salt pH tended to improve estimates of lime requirement. • The original A-E method had an R2 value of 0.85 when regressed on the SLR and overestimated LR approximately 224 kg ha-1. • The Moore-Sikora had an R2 value of 0.81 and over estimated LR approximately 300 kg ha-1. • The UGA had an R2 value of 0.74 and under estimated LR approximately 400 kg ha-1. Using Thompson’s adjustment formula came very close to the SLR mean but the R2 was not improved.