SOIL RESPIRATION AS A MEASURE OF SOIL BIO LOGICAL-ACTIVITY

Soil respiration is one of the oldest measured parameters of biologica l activity in soil. In the present study, soil respiration is measured as the carbone dioxide production of unamended soil in laboratory con ditions by absorption method. The study has been aimed at measuring re spiration of soils different in texture and climatic regions in depend ence on sampling time, C(org) content and contamination with heavy met als, respectively. The response of soil respiration to seasonal change in the period from March to November is expressed by proportion of it s maximal and minimal values measured in that period (index of maximum respiration/minimum respiration, Tab. I). The index of maximum respir ation/minimum respiration ranged between 1.2 and 7.3 in dependence on agricultural practices and year of measurement. The soil respiration m easured on early spring and late autumn data closely correlated to mea n values of soil respiration calculated from monthly samplings from Ma rch to November (Tab. II). In one locality (Tab. III), the data with t he same soil respiration were chosen from three-year studies. Although soil respiration did not differ, microbial biomass determined in thes e sampling data fluctuated from 159 to 1047 mug C.g-1. An identical so il respiration can reflect a high quantity of microorganisms with low activity, as well as low quantity of active microorganisms. Soil respi ration determined in soil samples of one type (cambisol) taken in earl y spring in one climatic region but differing by agricultural practice s 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 vari ous climatic regions, did not depend on C(org) (Tab V). The variabilit y 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 pr actices were higher than those connected with soil texture and climati c region. Soil respiration after contamination with heavy metals (arse nic and cadmium, Tab. VI) did not differ from the control during the w hole vegetation period. Concentrations of heavy metals used were too l ow to affect apparently such a complex as soil respiration is. Nitroge nase activity determined in the same soil samples was inhibited (S i m e k , 1993).