COMPARISON BETWEEN A CHEMICAL-METHOD AND A BIOLOGICAL-METHOD TO DETERMINE THE N-MINERALIZATION POTENTIAL OF TEMPERATE-HUMID REGION SOILS

The potentially mineralizable organic N of 33 different soils was esti mated by a chemical test (hot extraction with 2N KCl) and the values c ompared with those previously obtained by a biological method (aerobic incubation iii the laboratory). On average, the organic N solubilized by the chemical procedure was significantly lower than that mineraliz ed by a two weeks aerobic incubation for all the soils as a whole. The same was true for soils developed over acid rocks and over sediments. However, the values obtained for the soils developed over limestone a nd basic rocks were similar by both methods. The values obtained by bo th methods were not significantly correlated neither when considering all soils together nor when considering different groups according to soil management of parent material. Significant correlations between b oth methods were only found when the soils were separated into two gro ups according to their organic N content: soils with less than 400 mg N 100 g(-1) soil and soils with more than 400 mg N 100 g(-1) soil. The organic N solubilized by the chemical procedure was significantly cor related with the hexosamine-N content; however, it was not correlated with the factors that control the biological mineralization of the org anic N, except with the soluble Al content. Therefore, the chemical ex traction did not seem to address the biologically active N pool in a s elective way.