Organic carbon cycle, incidence of microorganisms and respiration activityin long-term field experiment

In order to determine long-term effects of organic and mineral fertilisers on soil organic matter, soil microorganisms and their activity and further soil properties, Novak has started a small plot field experiment in 1958. T o eliminate the effect of cultivated plants, he decided to carry out this e xperiment as a bare fallow. The experiment was founded on Luvi-haplic Chern ozem in Prague-Ruzyne. It consists of seven variants. Soil samples have bee n taken twice a year till 1979 and once a year since that time. Several che mical and microbiological analyses were performed over the whole time of th e experiment. The long-term data basis of this experiment was used to evalu ate organic and mineral fertilisation on the total carbon dynamics in soil, respiration activity, biomass and the incidence of soil microorganisms in soil. High doses of organic manure increased the soil organic carbon conten t. The carbon accumulation in these plots proceeded for about 13 years (195 8 to 1971, the first time period). During this time period, the effect of o rganic manure on the carbon content in soil was approximately additional. E xponential and polynomial regression curves showed, however, a better corre lation coefficients. None of these functions reflected the increasing miner alisation rate of the already present organic matter in soil. Later (1972 t o 1989, the second time period), there was no further apparent carbon accum ulation. A steady state equilibrium can be supposed in this time period, wh ich might be characterised by a slightly declining regression line. Accumul ated organic matter decomposition occurred later on, when no further manuri ng was applied (1990 to 1998, the third time period). Slight decrease (abou t 0.1% C-ox) of the carbon concentration occurred in control and mineral fe rtilised variants over the whole time of the experiment. This decrease was about doubled in the tilled variants. Organic manuring increased basal resp iration rate, mainly in the stationary time period. Average respiration rat e was more or less the same in the control and mineral fertilised variants in the first period. It increased in all these variants during the stationa ry phase and dropped down in the third period. Potential respiration (NG - glucose and ammonium sulphate added) has shown similar trends as those for the basal respiration. The most remarkable result is the drop down of the p otential respiration rate in mineral fertilised variants in the second time period, already. This is an evident change in the soil functionality cause d by high doses of mineral fertilisers. Average values of the biomass carbo n in the third period resembles the basal respiration rate and total carbon content in soil. The amount of biomass carbon per unit of the total carbon was similar in organic and control variants, while it was depressed in min eral fertilised variants. Organic manuring increased the average number of bacteria about twice, as compared to unfertilised controls, while mineral f ertilisation decreased their number to about a half of that in controls. Nu mber of bacteria dropped down in organic variants to the values determined in controls in the third period, when no further manuring was applied. Numb er of micromycetes was much less affected by organic manuring and mineral f ertilisation. Their number increased in mineral fertilised variants in the third period. Incidence of bacteria in soil samples was evidently dependent on the presence of fresh organic matter rather than on the total carbon co ntent in soil.