Influence of nitrogen concentration and form in the nutrient solution on N2O and N-2 emissions from a soilless culture system

The influence of nitrogen concentration and form in the nutrient solution on the N2O and N-2 emissions from a closed rockwool system with cucumber crops was investigated. At optimum, nitrate-accented nitrogen supply of plants (120 mg N l(-1)) on average 0.59 kg N per hectare greenhouse area and day was released. Comparable emission rates occurred with moderate sub- and supraoptimum nitrogen fertilization. Thus, in this range the N supply was non-limiting For the gaseous nitrogen losses. Only in the case of severe suboptimum N supply (40 mg N l(-1)) the N2O and N-2 emissions were clearly lower, probably as a result of diminished plant growth and therefore reduced root respiration and exudation of organic carbon sources for microorganisms. The proportion of nitrous oxide in the gaseous nitrogen losses increased on average from 5 to 13% with increasing N supply, possibly because of an impaired N2O reduction in denitrification due to high nitrate ,concentrations, Short-term shifting with optimum nitrogen supply from nitrate-accented composition to pure nitrate did not affect the gaseous nitrogen emissions, whereas an exclusive ammonium supply resulted ina considerable decrease; The results indicated that the N2O emission and the total nitrogen losses from the soilless culture system were predominantly caused by denitrification.