Abstract
Field trials were carried out at the experimental cereal breeding fields in Stende (Latvia), an area characterized by a northern temperate climate. The soil had been under short-term organic or conventional crop management and was then subjected to crop rotation, using buckwheat (Fagopyrum esculentum Moench.) and potato (Solanum tuberosum L.) as the forecrops; wheat (Triticum aestivum L.) and oat (Avena sativa L.) as the following crops; and two fertilizer regimes under common organic and conventional practices. As the evaluation criteria of the soil quality, physico-chemical (pH value, organic matter, N, P, K) were tested. In addition, the following biological properties were estimated: plate counts of different physiological groups of microorganisms, soil microbial respiration, enzymatic activity (urease, dehydrogenase and fluoresceine diacetate hydrolysis) of soil microorganisms. Soil microbial respiration activity, FDA hydrolysis and urease activity showed a tendency to decrease in the soil after potato cultivation as the forecrop. The number of bacteria was higher in plots with wheat, and the actinomycete count was lower after oat cultivation. The number of bacteria, actinomycetes, fungi, as well as soil microbial respiration and enzymatic activity, fluctuated due to weather seasonality.