Low nitrate retention capacity in calcareous soil under woodland in the karst region of southwestern China

Abstract

A 15N-tracing study was conducted to investigate the gross N transformation rates involved in the production and consumption of NH4+ and NO3− in karst region soils (a calcareous and a red soil) from southwest China under woodland. The gross mineralization rate of organic N to NH4+ was much lower in calcareous soil (3.71 mg N kg−1 d−1) than in red soil (5.57 mg N kg−1 d−1), while the total gross nitrification rate was significantly higher in calcareous soil (5.80 mg N kg−1 d−1) than in red soil (0.70 mg N kg−1 d−1). Microbial NO3− immobilization accounted for 2.9% and 153% of the total nitrification in calcareous soil and red soils respectively. Thus the calcareous soils in the karst region have a low biological N retention capacity and high N losses, which are further aggravated by the high precipitation and fractured soil structure.