The 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 Szent István University in Gödöllő on brown forest soil (luvic calcic phaeozem) in 2007–2009. Two nutrient doses (0 kg ha-1 N, 50 kg ha-1 N) were applied in the experiment.

The major characteristics of the experimental site are as follows; the average annual temperature is 9.4 °C, the average annual precipitation is 590 mm. The average precipitation is 150 mm in the most crucial months of August through October. In 2007 and 2008, the amount of precipitation was ordinary with respect to secondary crops with 169.4 mm and 130.8 mm of rainfall in August-October. However, 2009 was dry, only 32.0 mm of rainfall was measured during the growing season of green manure crops. The crop year effect was strong, especially on fields without fertilisation.

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: 311% for phacelia, 309% for mustard, and 278% for oil radish in the average of three years. The dry matter content of green manure crops was shown 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 455.9 kg and dry matter increased by 31.8 kg as a result of one kilogram of nitrogen active substance in the average of three years. The green mass of mustard increased by 377.9 kg and the amount of dry matter increased by 43.5 kg. The green mass of oil radish increased by 342.9 kg and the dry matter content increased by 26.6 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 also increased as a result of nitrogen application, 3.32/2.89/2.63 times in phacelia, 3.73/2.63/2.94 times in mustard and 3.54/2.62/2.51 times in oil radish in the average of 2008–2009, respectively. The amount of plant tissue nitrogen increased with each extra 1 kilogram of nitrogen active ingredient by 1.4 kg in phacelia, 3.0 kg in mustard and 2.1 kg in oil radish in the average of 2008-2009. Plant tissue phosphorus and potassium contents were also affected by N fertilisation. P2O5 increased by 0.4 kg per kg in phacelia and 0.6 kg per kg in both mustard and oil radish. K2O contents were as follows: 1.7 kg per kg in phacelia, 2.6 kg per kg in mustard and 1.8 kg per kg in oil radish.

According to our studies, all three plant species were shown 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) were shown to be more favourable than phacelia. Based on the obtained results, 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, green manure crops, phacelia, mustard, oil radish