Cultivation effects on soil biological properties, microfauna and organic matter dynamics in Eutric Gleysol and Gleyic Luvisol soils in New Zealand

Information on the influence of duration of cultivation on soil organic mat ter (SOM) dynamics is needed by researchers, policy makers and farmers for assessment of global ramifications of carbon (C) sequestration and agricult ural sustainability. This paper examines the changes in microbial biomass c arbon (MBC) and nitrogen (MBN), metabolic quotient (qCO(2)). microfaunal po pulations, and C and N mineralisation to assess the effect of cultivation o n SOM dynamics. Cultivation. for up to 34 years, of soils previously under permanent ryegrass (Lolium perenne L.) and clover (Trifolium sp.) pastures, resulted in a 30-60% decline in concentration of soil organic C and N, and had a significant influence on soil biological parameters in two New Zeala nd (Eutric Gleysol, Kairanga silty clay loam and Gleyic Luvisol, Marton sil t loam) soil types. Cultivated soils had consistently fewer MBC and MBN con tents, and higher qCO(2) than their counterparts in permanent pastures. Cha nges in the soil microfauna following cultivation were consistent with chan ges in microbial biomass. Both the amount and proportion of mineralisable N were also reduced with cultivation. In the pasture soils C mineralisation rates (under laboratory conditions) were twice those (ca. 15 mg (CO2-C) kg( -1) soil) in the 5-20 year cultivated soils (ca, 7 mg (CO2-C) kg(-1) soil), and were reduced to one-half (ca. 3.5 mg (CO2-C) kg(-1) soil) in the 34-ye ar cultivated soil. Over 112 days, the soils lost approximately 2.4-5.0% of their total C, and 1.4-5.0% of total N was mineralised. The percentage C l oss also differed with oil type, with Marton silt loam (260 g kg(-1), clay) soil losing one and half times as much percentage C as Kairanga silty clay loam (420 g kg(-1), clay) soil. Despite greater C mineralisation in soil f rom pasture, more C and N were conserved in it than in the cultivated soils . As annual C inputs in cultivated soils are smaller than the C decompositi on. this would result in a negative soil C balance. The shifts in microbial biomass, its metabolic quotients and soil microfauna appear to be associat ed with differences in the quantity and 'quality' of inputs and SOM decompo sition rates, and reflect the land-use change ft om pasture to continuous c ultivation. (C) 2001 Elsevier Science B.V. All rights reserved.