Note on the unparallel vertical distribution of nitrate and sulfate in Mollisols

Abstract

Soil fertility diagnosis often omits subsoil measurements, impacting precision. Ourobjective was to compare the vertical distribution of nitrate and sulfate in agriculturalMollisols. Both anions were measured in 34 Mollisols of the Pampean region(Argentina) sampled to 160-cm depth at 20 cm intervals. Nitrate exhibited a continuousdownward trajectory, with maximum values at 0–20 cm (12.7 mg N kg−1) andminimum values at 140–160 cm (3.3 mg N kg−1). Sulfate displayed a sinuous pattern,with a minimum at 60–80 cm (3 mg S kg−1). The 60–160/0–160 cm concentrationratio was 42% for nitrate and 60% for sulfate, indicating greater topsoil stratificationfor nitrate. Predicting deep-layer nitrate concentrations from topsoil data was moreaccurate than for sulfate. This poses a challenge for assessing soil S bioavailability,as subsoil sulfates go undetected in conventional sampling.