Development and chemical composition of three green manure species (phacelia, mustard, oil radish) produced in a double cropping system were examined at the pilot farm of the Szent István University in Gödöllő on brown forest soil (luvic calcic phaeozem) in 2010–2011. Two nutrient doses (0 kg ha-1 N; 50 kg ha-1 N) were applied in the experiment.

A small amount of 50 kg ha-1 nitrogen active ingredient resulted in the increment of biomass of all three crop species. Yield figures were as follows: 248% for phacelia, 304% for mustard, and 211% for oil radish averaged over two years. Dry matter content of green manure crops proved to be less than that of green mass due to the increase of water content as a result of nitrogen application. The green mass of phacelia was increased by 456.6 kg and dry matter was increased by 48.3 kg as a result of one kg of nitrogen active substance averaged over two years. The green mass of mustard was increased by 383.9 kg and dry matter was increased by 57.8 kg. The green mass of oil radish was increased by 383.3 kg and dry matter was increased by 27.1 kg. However, without the application of nitrogen, a sufficient amount of biomass was not always achieved on the control plots.

The amount of NPK of plant tissues was also increased as a result of nitrogen application. 2.06/2.23/2.05 rate in phacelia, 2.22/1.98/1.96 rate in mustard and 1.81/1.94/1.62 rate in oil radish averaged over 2010–2011, respectively. Plant tissue nitrogen content was increased by each extra 1 kilogram of nitrogen active ingredient by 1.6 kg in phacelia, 1.8 kg in mustard and 1.3 kg in oil radish averaged over 2010–2011. Plant tissue potassium and phosphorus contents were also affected by N fertilization. P2O5 was increased by 0.7 kg per kg in phacelia, 0.6 kg per kg in mustard and 0.8 kg per kg in oil radish. K2O contents were as follows: 2.1 kg per kg in phacelia, 1.6 kg per kg in mustard and 1.1 kg per kg in oil radish.

According to our studies, all three plant species proved to be suitable for green manure use in terms of soil protection and organic matter improvement. However, considering biomass per hectare and chemical composition values, mustard and oil radish (family Brassicaceae) proved to be more favourable than phacelia. Based on the results obtained, nitrogen applications are suggested to be done in certain production areas in the case of green manure crops, especially where the straw residues of cereals remain on the stubble.

Keywords: green manure, nitrogen, phacelia, mustard, oil radish