1. Soil pH and SMP Buffer pH methodologies a.Time for SMP buffer to set in soil-water slurry b. Conditions on LabFit for soil pH and Sikora buffer pH 2. Laboratory survey on pH and lime recommendations prepared for SERA-6 conference June 4-5, 2007 F.J. Sikora University of Kentucky Soil pH and buffer pH methodology: water and SMP/Sikora buffer reaction time with soil and a laboratory survey

Variations in methods for determining 1:1 soil:water pH Reference pub Quantity of soil Stirring (or mixing) time after adding water Standing time before determining pH Stirring during/before pH measurement SPAC, Inc.4.25 cm 3, 5 g, or 10 cm 3 Stir for 5 sec10 minstir during pH measurement Southern10 cm 3 Mix for 5 sec30 minstir soil suspension by swirling the cup slightly just prior to reading pH NortheasternScoop 5 cm 3 or weigh 5 g Stir vigorously for 15 sec 30 minplace electrodes in the slurry, swirl carefully and read pH immediately North Central 4.25 cm 3 (5 g scoop) Stir vigorously for 5 sec 10 minplace electrodes in the slurry, swirl carefully and read pH immediately Western 5  0.1 g Stir thoroughly for 5 sec 15 minplace electrodes in the slurry, swirl carefully and read pH immediately

Variations in SMP methods for determining buffer pH Reference pub Quantity of soil Volume of buffer added to soil pH slurry and shaking time Oscillations/min Standing time before determining pH SPAC, Inc.4.25 cm 3 or 5 g10 mL buffer, shake for 10 min (or 15 min) >18030 min (or 15 min) Southern NortheasternScoop 5 cm 3 or weigh 5 g 10 mL buffer, shake for 10 min (or 15 min) min (or 15 min) North Central4.25 cm 3 (5 g scoop) 10 mL buffer, shake for 10 min (or 15 min) min (or 15 min) Western 5  0.1 g 10 mL buffer, stir every 5 minutes for 20 min 20 min

Mclean, Eckert, Reddy, and Trierweiler An improved SMP soil lime requirement method incorporating double-buffer and quick-test features. SSSAJ 42: excerpt from 1975 North Central publication on soil test methods.

Table in the current North Central region publication on soil test methods. SMP Buffer pH

LEXINGTON LAB

PRINCETON LAB

buf

stirring time for buffer in soil time buffer set in soil prior to measurement LabFit method with Sikora buffer 0.33 min. ± min. ±4±4 1.5 hrs for 3 trays (n=120) Method for adding water to soil Each sample stirred with stir rod and let set for 30 min.

Sikora Buffer pH, LabFit instrument Soil pH, LabFit instrument Soil pH, NAPT medianSMP Buffer pH, NAPT median Soil pHBuffer pH 1:1 line regression line

Soil pH, LabFit instrument Soil pH, NAPT median Each sample stirred with stir rod for 5 sec and let set for 30 min. Tray swirled for 5 sec. and let set for 30 min. 1:1 line regression line Soil pH

A Mid-Atlantic Soil Testing and Plant Analysis Work Group survey on methods for soil pH, buffer pH and lime recommendations Objectives are to assess: 1. variation in lab methods being used. 2. effect of method variation on intra- and interlaboratory error. 3. variation in how lime recommendations are made. & SERA6

Soil pH MAD values in the NAPT program

SMP Buffer pH MAD values in the NAPT program

extra slides

Variations in methods for Mehlich III extractable nutrients Reference pub Quantity of soilVolume of Mehlich IIIMixing time and method SPAC, Inc.5 cm 3 50 mL5 min on reciprocating shaker Southern2.5 cm 3 25 mL5 min on reciprocating shaker NortheasternScoop 2.5 cm 3 or 2.5 g (references orig. method on 10:1 ratio based on vol.) 25 mL5 min on reciprocating shaker at 200 epm North Central 1.7 cm 3 (2 g scoop) 20 mL5 min on shaker at 200 or more epm between 24 to 27 o C Western 2  0.05 g 20 mL5 min on reciprocating shaker