Effects of previous intensive agricultural management on microorganisms and the biodiversity of soil fauna

In this study effects of previous intensive management on microorganisms and soil fauna were investigated. It was hypothesized that a former but now abandoned intensive management practice still causes negative effects years after conversion into conventional management.Two agricultural fields were investigated. Until 1990 one field (preINT) had been managed with the intensive crop hops (Humulus lupulus), whereas the second one (preCON) had been under crop rotation. In consequence the main difference between the two fields was the high copper load of preINT. In the period during this study both fields were cultivated the same way (1991: winter wheat, 1992: spring barley).Microbial biomass, species numbers and abundances of collembola as well as of earthworms were much lower in preINT in the first year of investigation. In 1992, earthworm biomass was still extremely low, whereas the microbial biomass and total collembola had reached the values of preCON. Between the collembola populations there were still distinct differences in species abundances. In preCON,Folsomia quadrioculata, Onychiurus armatus, and theMesaphorura krausbaueri group each made up about 1/4 of the total population. In preINT nearly 60% of the population consisted of theMesaphorura krausbaueri group, followed byIsotoma notabilis andOnychiurus armatus.Folsomia quadrioculata andIsotomiella minor in preINT exhibited extremely small abundances during the whole investigation period. Thus, in comparative field studies their abundances could serve as indicators for copper contamination.Supplementary microcosm studies had shown that severe reductions of earthworm numbers, especially with simultaneous high mesofauna abundances, will be accompanied by increased mineralization rates. Therefore changes in soil fauna composition caused by copper contamination could have pronounced effects on mineralization rates and nutrient fluxes.