Articles
SOIL MICROBIOLOGICAL ACTIVITIES IN ORGANIC AND CONVENTIONAL VEGETABLE GARDENING – A SENSITIVE INSTRUMENT OF HORTICULTURAL RESEARCH
Although several investigations about soil microbiology in organic agriculture have already been performed, there are only a few dealing with organic horticulture.
Object of this investigation is a long-term trial with the factors "production system" (organic, conventional, untreated) and "plant species" (six vegetables). From 1989 to 1991 soil samples were taken at seven dates (spring, summer, autumn). Microbial biomass was estimated by substrate-induced respiration (SIR). Soil respiration (SR) and six soil enzyme activities (dehydrogenase, xylanase, phosphatase at two pH-levels, protease, urease) were measured, metabolic quotients (i.e. specific respiration, qCO2) were calculated.
In this study all soil microbiological activities (respiration and enzymes) are not only expressed as "absolute activity" (i.e. activity per unit soil), as usual, but also as "specific activity" (i.e. activity per unit microbial biomass). This allows to observe the physiological activity of the microorganisms, while absolute activities contain both the information of activity and biomass.
SIR is quite constant at the organic and the untreated plot.
The conventional plot shows pronounced seasonal fluctuations and a heavy but short-term increase after organic manuring.
Although SIR of the organic plot is constant, organic manuring influences its SR more than one year.
As the qCO2 points out the microorganisms really increase their metabolic activity, while fluctuations of the SR of the conventional plot just reflect changes of microbial biomass.
The metabolic activity of the microorganisms from the untreated plot is unexpected high.
Differences in growth and physiological behaviour are rooted in the different nutrition because of the cultivating system and indicate an adaptation of the microbial society to that.