Changes in enzyme activities as affected by green-manure catch crops and mineral nitrogen fertilization
The estimation of soil microbial activity has been an important research issue because of the significant role that microorganisms play in nutrient cycling in soil. In a 3-year (August 2005 -August 2008) experiment, the effect of catch crops: oilseed radish (Raphanus sativus var. olifera L.) and field pea (Pisum sativum L.) vs. plots without a catch crop, and inorganic nitrogen (N) fertilization at 0, 40, 80, 120, 160 kg ha -1 year -1 on soil dehydrogenase (DH), catalase (CAT) and fluorescein
... ) and fluorescein diacetate hydrolysis (FDAH) activities were investigated on albic, cutanic Luvisols (LVab, LVct). The catch crops were sown at the beginning of August and ploughed in autumn in 2005, 2006 and 2007. Then the main crop, spring wheat (Triticum aestivum L.), was grown in 2006, 2007 and 2008. Soil samples were taken twice a year, before spring wheat sowing (March or April) and after harvesting (August). Generally, catch crops significantly influenced DH and CAT activities in all of the years of the investigation, while FDAH activity was affected only in 2007. There were higher DH and FDAH activities in catch crop treatment versus the control and only in some cases in field pea than in oilseed radish when both catch crops treatments were compared. DH and CAT activities were always higher in August than in March or April. Nitrogen fertilization influenced DH and FDAH activities only in 2007, while CAT activity was influenced during the entire experimental period (2006)(2007)(2008). Generally, the highest CAT activity was noted at N rates of 80 or 120 kg ha -1 year -1 . Chemical properties (organic carbon, total nitrogen, pH 1 M KCl) were not significantly affected by catch crops and inorganic N fertilization treatments. The studied indices of microbial biomass were significantly correlated with chemical soil properties.