Milja Vepsäläinen

The impact of crop plant cultivation and peat amendment on soil microbial activity and structure

AbstractA rapid means for restoring soil fertility could be addition of peat to the plough layer. The impact of cultivation of eight different crops (the joint impact of plant and the management tailored for each plant), with and without soil amendment by peat treatment on soil microbiological, physical and chemical properties was assessed for two consecutive growing seasons. As a measure of the functional diversity of soil microbial community we estimated the activity of several different extracellular soil enzymes using the ZymProfiler® test kit. ATP content was measured to yield information on the amount of the active microbial biomass, and phospholipid fatty acid (PLFA) profiles were analysed to reveal the microbial community structure. The enzyme activity patterns of the soil samples indicated several differences due to the different crops and years but ATP content and PLFA profiles were rather stable. However, microbial biomass as total amount of PLFAs depended on the plant and peat treatment and ATP content varied between the years. The effects of the peat treatments were less clearly indicated by the biological parameters one or two years after the amendment, as only arylsulphatase and β-xylosidase activities were affected in both the years. Soil moisture, affecting enzyme activities, depended on the year and crop plant and peat addition increased it. Abbreviations: AMC – 7-amino-4-methylcoumarin; AP – aminopeptidase; ATP – adenosine triphosphate; Cmic– microbial biomass carbon; DNA – deoxyribonucleic acid; EC – electrical conductivity; FAME – fatty acid methyl ester; fw – fresh weight; MUF – 4-methylumbelliferyl; na – not added; Nmic– microbial biomass nitrogen; PDE – phosphodiesterase; PLFA – phospholipid fatty acid; PME – phosphomonoesterase; SOM – soil organic matter

Poor enzyme recovery by extraction from soils

The extraction of enzymes from soil would be an ideal way to measure various soil enzyme activities. This method would be especially useful for determining activities in small volumes (i.e. microtiter plates). Compared to incubation of bulk soil with buffer, an extract is more convenient to handle and more homogenous when working with small volume samples. In this study an attempt was made to extract enzymes from two different soil samples using various buffers. The efficacy and reliability of the extraction differed regarding the buffer composition and concentration, and varied from soil to soil. In general, only a few percent of the enzyme activity of whole soil was observed in the extracts, indicating the need to use whole soil samples in enzyme assays.