Hot water extractable C and N in relation to microbiological properties of soils under beech forests

Hot water extraction is sometimes recommended as an easy method to estimate the readily mineralizable fractions of total C (C-t) and total N (N-t) in arable soils. However, the usefulness of this method for forest soils has not been adequately studied. The objectives of this study were to relate the hot water extractable C (C-hw) and N (N-hw) to microbiological and chemical properties of the forest soils under beech (Fagus sylvatica L.) stands and to test the ability of near infrared spectroscopy (NIRS) to predict chemical and microbial properties of these soils. Soils differing in humus type, soil type and soil texture were collected from five locations and five depths. In all soils the amount of C-hw was higher than the microbial biomass C (C-mic) indicating that a considerable part of C-hw was of non-microbial origin. The amount of C-hw in mineral soil correlated significantly (r =-0.30-0.53) with C-mic, basal respiration (BAS) and C-t/N-t ratio but was not related to C-mic/C-t ratio. The amount of N-hw was correlated with C-mic, BAS, C-mic/C-t ratio, and C-t/N-t ratio (r =-0.59-0.78). However, C-t and N-t values showed better relationships (r =-0.42-0.88) with all the parameters, indicating no advantage in using C-hw and N-hw in forest soils. NIRS predicted satisfactorily C-t, N-t, C-hw, N-hw, C-mic, C-mic/C-t ratio and BAS in the mineral soils [the regression coefficients (a) of linear regression (measured against predicted values) ranged from 0.84 to 1.17 and the correlation coefficients (r) ranged from 0.86 to 0.94] indicating the applicability of NIRS to estimate these properties.