Nature, distribution and ameliorative response of soil acidity in a test site of hot dry sub-humid belt of West Bengal

A study was undertaken in hot dry sub-humid region (Patloi Nala micro-watershed), under red and lateritic belt of Purulia district, West Bengal, India 23°21′to 23°23′23′′N and 86°29′47′′to 86°31′35′′E) to investigate the nature, distribution and ameliorative response of soil acidity. The study revealed that most of the area was dominated by Alfisols followed by Inceptisols and Entisols. Clay content varied from 6.8 to 36.3%. Surface soil texture was coarser than lower horizons. All the profiles were characterised by higher organic carbon (0.4–10.4 g kg⁻¹) at the surface than the lower horizons. Free iron oxide content (24.0–42.0 g kg⁻¹) in most of the soil series was higher in the surface than the sub-surface and sub-soil. The surface soil showed more acidity [pH (water), 4.5–6.1] than the horizons underneath [pH (water), 4.65–7.92]. pH (KCl) (3.4–6.5) showed lower values than pH (water) for all the identified soil series, indicating the dominant presence of reserve acidity in that area. Physiography-wise no particular trend of any soil acidity was observed. Lime potential varied from 1.88 to 4.40 and had significant positive correlation (0.627, at 1% level with 10 d.f.) with the soil + SMP lime buffer pH, indicating the less buffering capacity of the soil at greater lime potential. The contribution of “exchange acidity” [0.10–1.50 cmol (p⁺)kg⁻¹] to “total potential acidity” [2.82 – 18.2 cmol(p⁺)kg⁻¹] was negligible compared to the “pH dependent acidity” [2.82–18.0 cmol(p⁺)kg⁻¹]. Free Fe₂O₃ mostly influenced “exchange acidity” and showed significant (at 1% level, 30 d.f.) positive correlation (0.621), whereas, organic carbon was the most important factor influencing “pH-dependent acidity” (0.949, significant at 1% level, 30 d.f.). The study also indicated that 57.7% area was under surface pH (range) less than 5.0 whereas, 34% area required 5.75–13.5 t ha⁻¹ line in the form of CaCO₃, which was highest in that area. The amelioration of soil acidity by lime application ranges in particular areas could be obtained from the GIS map.