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Parameters characterizing N mineralization and nitrification were measured in soils of ten monitoring areas of the basal soil monitoring carried out by the Central Institute for Supervising and Testing in Agriculture. A remarkable seasonal cycle was found only for nitrate concentrations that reached their maxima in the spring (April-June), and late summer and/or autumn, starting in August. Ammonium ions were nitrified immediately after fertilizer application. Anaerobic N mineralization represented a variable parameter, which was not directly affected by mineral N fertilizers. Nitrification measured by means of one-week incubation was significantly stimulated by N fertilizers confirming that substrate availability was a limiting factor of this process. Short-term nitrification activity (SNA) showed no remarkable seasonal fluctuations, which meant that the potential nitrification rate remained relatively constant during the season. Urease activity was mostly constant during the year and was only slightly related to N mineralization.

The development of soil limiting values of the protection of the quantity and mainly quality of the crop production tends from empiric values towards critical values, based on ecotoxicity. We present an attempt to derive transfer functions by the means of multiple regression analysis. The substitution of trace elements contents in crops in the prediction equations for fodder or food standards or phytotoxicity limits satisfies the present ecotoxicological demands. We preferred polyfactor relations to simple ones. The exceeding of reference values must be verified by the determination of the hazardous transfer in the field. Therefore the reference values are called testing values. They were derived especially for Cd, Pb, As, Cu, Zn, Ni and Mn. For some trace elements, only protective values can be set up (especially for Cr, Hg, but also for Tl, Be, V). They reflect minimum values that guarantee growing crops without any risks. Experimental data (pot trials) were compared with results obtained in field investigations. The resulting critical values were also compared with the values proposed in Germany.

The conception of these investigations is based on the premise that a way should be found to eliminate, or at least mitigate, the harmful effect of excessive soil acidity without resorting to the massive and costly measures of liming. The main issue addressed in this study is how to increase crop yield by increasing nutrient availability rather than how to neutralize the soil. This as well as our earlier investigations, conducted on pseudogley of mesoelevations, indicate that this can be achieved by the application of special natural amendments (SNA) based on zeolite tuff, under the name Agrarvital (AV), in which clinoptilolite prevails while the remaining part is a mixture of soft lithothamnian limestone and dolomite (SLL+D). These amendments enhance ion exchange in the soil and their activation at a considerably lower pH than it is the case after liming. Fertilizing value of Agrarvital (AV) and lime materials (LM) was evaluated according to the yields achieved and some yield components of the crops grown. The results point to the good fertilizing effect of AV upon yields of winter wheat, maize, soybean and winter barley, equal to or better than the effect of conventional LM applied at several times higher rates.

Effects of increasing doses of the herbicidal preparation Sencor 70 WP (metribuzin a.i.) on selected potato varieties were studied in a field and pot experiments using very rapid fluorescence induction (vrFI). Tuber yield, and in pot experiments a tuber number and characteristics of the aboveground biomass were assessed. The curve of rapid induction goes through the O-J-I-P phases. The parameters Fo, Fv/Fp and rFj were measured. Based on changes in the vrFI parameters in comparison with controls, varieties were ranked according to sensitivity to metribuzin in field experiments. Keřkovské rohlíčky and Ukama were the most sensitive varieties and Impala the least sensitive variety. In pot experiments in the growth chamber, significant decrease in tuber weight vs controls was found in sensitive varieties Keřkovské rohlíčky (in 1998, 0.75 kg.ha^-1 Sencor 70 WP decreased tuber weight by 28% and 1.5 kg.ha^-1 by 89%) and Ukama (in 1997, at 1.5 kg.ha^-1 by 35%). Under stable conditions in the growth chamber, there were lower differences in the rFj parameter in these varieties in comparison with controls than in resistant ones. Based on this finding it can be assumed that the sensitivity of varieties can be determined according to rFj changes under stable ambient conditions.