The aim of the study was to ascertain the impact of irrigation or its absence on respiratory and dehydrogenase activities in soils under maize growth. Investigations were carried out in years 2007-2009 at six times of analysis during the maize growth season. The experiment included experimental plots on which maize of Clarica hybrid (FAO 220, Pioneer) intended for CCM was grown. The experimental plots were irrigated with the use of semi-permanent sprinkling machines. Dehydrogenase activity in the soil was determined colorimetrically, and soil respiratory activity was determined with the titration method. Soil respiratory activity did not exhibit significant variability during the growth season with the exception of 2009 at the second time of analysis (at the 2-3 maize leaf stage), when the highest average values in the season were recorded. In the third year of the analysis (2009), practically speaking, no significant differences were observed in the activity of the examined enzymes between irrigated and nonirrigated plots. The comparison of the dates of the analyses showed that the highest activity of the investigated enzymes occurred in the spring before sowing and in the summer. Mean values of the respiratory activity did not show large differences in the individual seasons.

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