Extractable nitrogen using hot potassium chloride as a mineralization potential index

Inorganic nitrogen (N) in soils is a primary component of soil-plant N buffering. This study was conducted to determine if non-exchangeable ammonium-nitrogen (NH4-N) could serve as an index of potentially mineralizable organic N which is an important sink in N buffering. Four long-term winter wheat (Triticum aestivum L.) experiments that had received annual fertilizer N at 0 to 272 kg N hal were used. Soils from these experiments were extracted by four 10 mt portions of 2M potassium chloride (KCl) at room temperature followed by extraction with 20 mt of 2M hot KCl. Extraction at 100 degrees C for four hours using 3 g soil and 20 mL 2M KCl was found to be the most effective. Hot KCl-extractable NH4-N minus room temperature KCl-extractable NH4-N was considered non-exchangeable NH4-N. Non-exchangeable NH4-N was correlated with the long-term N rates, and believed to be a reliable index of potentially mineralizable organic N. The relationship was linear for NH4-N where the lowest N rate had the lowest extractable N. The mean non-exchangeable NH, N concentration ranged from 8.42 to 16.34 mg kg(-1); whereas, nitrate-nitrogen (NO3-N) ranged from 0.07 to 1.87 mg kg(-1). Total inorganic N extracted was similar to that mineralized in a 42-day aerobic water saturated incubation. In addition, using a linear-plateau model, extractable NH4-N was highly correlated with long-term average yield(R-2=0.92). For the soils evaluated, this method provided a rapid measure of potentially mineralizable N.