SOIL PROBE LUBRICATION AND EFFECTS ON SOIL CHEMICAL-COMPOSITION

Deep soil-profile sampling in wet, clayey soils can be difficult. Fric tion against the probe surface can cause core compression and impedes extraction of intact cores from the probe tube. Lubrication of the pro be tube reduces friction and improves core extraction. Two studies wer e conducted to determine soil-sample contamination resulting from prob e lubrication and possible interactions with probe diameter (surface-a rea:volume ratio) and sampling depth. Soils were sampled following pro be lubrication and analyzed for organic matter and seven common nutrie nts. Lubricants tested contained varying amounts of organic matter (24 ->700 g/kg), nitrate-N (NO3-N, 3-205 m/kg), phosphate-P (PO4-P, 244 mg /kg), potassium CK, 2-1200 mg/kg), and zinc (Zn, <0.1-460 mg/kg) but r elatively small amounts of manganese (Mn, <0.1-0.2 mg/kg), iron (Fe, 0 .2-2.9 mg/kg), and copper (Cu, <0.1-0.6 mg/kg). Macronutrient content of soil samples was not affected by lubrication beyond variation typic al among replicated soil samples from the study site. Differences amon g sample NO3-N, PO4-P, and K concentration means were not significant at the 0.05 probability level in either of the studies conducted. Samp le organic matter content was significantly increased by some lubrican ts in one study. Iron, Mn, Zn, and Cu were significantly affected in o ne or both studies. Lubrication reduces sampling time and frustration in wet, clayey soils and generally introduces negligible contamination when sampling for macronutrients. Lubrication may not be acceptable w hen testing for micronutrient metals.