SOIL RESPIRATION AS A MEASURE OF SOIL BIOLOGICAL-ACTIVITY

Soil respiration is one of the oldest measured parameters of biological activity in soil. In the present study, soil respiration is measured as the carbone dioxide production of unamended soil in laboratory conditions by absorption method. The study has been aimed at measuring respiration of soils different in texture and climatic regions in dependence on sampling time, C(org) content and contamination with heavy metals, respectively. The response of soil respiration to seasonal change in the period from March to November is expressed by proportion of its maximal and minimal values measured in that period (index of maximum respiration/minimum respiration, Tab. I). The index of maximum respiration/minimum respiration ranged between 1.2 and 7.3 in dependence on agricultural practices and year of measurement. The soil respiration measured on early spring and late autumn data closely correlated to mean values of soil respiration calculated from monthly samplings from March to November (Tab. II). In one locality (Tab. III), the data with the same soil respiration were chosen from three-year studies. Although soil respiration did not differ, microbial biomass determined in these sampling data fluctuated from 159 to 1047 mug C.g-1. An identical soil respiration can reflect a high quantity of microorganisms with low activity, as well as low quantity of active microorganisms. Soil respiration determined in soil samples of one type (cambisol) taken in early spring in one climatic region but differing by agricultural practices ranged from 8.9 to 42.1 mug CO2-C.g-1.d-1 (Tab. IV). The relation to C(org) was not found. Soil respiration, which was determined in soils with different texture (sandy loam, loam and clay loam) and from various climatic regions, did not depend on C(org) (Tab V). The variability of soil respiration in various plots within one soil texture and one climatic region was high - coefficient of variation ranged between 14 and 178 %. The differences in soil respiration due to agricultural practices were higher than those connected with soil texture and climatic region. Soil respiration after contamination with heavy metals (arsenic and cadmium, Tab. VI) did not differ from the control during the whole vegetation period. Concentrations of heavy metals used were too low to affect apparently such a complex as soil respiration is. Nitrogenase activity determined in the same soil samples was inhibited (S i m e k , 1993).