Sample Extraction Procedure (Mehlich 1)After samples are checked for proper order, labeled with Check and Blank locations noted, samples are ready for extraction.
- Using a 4 mL volumetric scoop (assume 5 g), measure an amount of soil from each sample box using the following method:
- Dip scoop with sweeping motion and fill to overflowing
- Hold scoop over box and firmly tap handle three times to settle
- Strike off excess soil with leveling rod and transfer
- Measure samples into extraction racks containing 10 polyethylene cups each. A Check sample is scooped at the appropriate location from a separate Check sample box or no sample is scooped at the blank location.
- Extract fifty samples at a time. Add twenty milliliters of Mehlich 1 extracting solution (0.05N HCl + 0.025N H2S04) by automatic pipette to each sample.
- Shake samples on a mechanical reciprocating shaker, adjusted to 180 oscillations per minute with a 4 cm stroke, for 5 minutes.
- Place prefolded, high quality filter paper, moistened with deionized water into funnel tubes in racks that correspond with the extraction racks.
- After shaking, immediately filter and save the collected extract for mineral analysis (P, K, Ca, Mg, Na, Zn, Mn, Cu, B). Transfer to test tubes for ICP.
- All glassware and cups should be thoroughly rinsed between samples with deionized water. Weekly wash glassware using a minimum of detergent and rinse thoroughly.
Mehlich 1 Extracting Solution (0.05 N HCl + 0.025 N H2S04)
To prepare 18 liters: add 77 mL concentrated HCl and 13 mL concentrated H2S04 to approximately 15 liters of deionized water in 20 liter carboy. Bring to 18 liters with deionized water and mix thoroughly.