Elimination of nitrate leaching to the ground water by planting energy-forest

László Tolner¹ – György Füleky¹ – Imre Vágó² – Marianna Sipos² – Imre Tolner³ – Kornél Szalay³ –– László Fenyvesi³

¹Szent István University, Department for Soil Science and Agricultural Chemistry, Gödöllő, Hungary

²University of Debrecen, Department for Agricultural Chemistry and Soil Science, Debrecen, Hungary

³Hungarian Institute of Agricultural Engineering, Gödöllő, Hungary

Nitrate ions can reach through their infiltration into deeper soil layers the ground water without any barrier, where they may cause serious contaminations. Regarding the leaching process it is totally unimportant, whether nitrate ions reached the soil through chemical fertilizers, manure, communal or agricultural wastewaters or such sewage sludge. The possibility of the microbial transformation of the nitrogen-containing material is even less parallel to the deeper soil layers.

At Gödöllő – Szárítópuszta (Hungary) long-term plant nutrition field experiments were carried out over 20 years on a Ramann-type ferruginous soil. Within this experiment the effect of different nitrogen fertilizer dosage (0-360 kg ha^-1) was investigated on the maize (Zea mays L.) production. During this period different, but significant amount of nitrate (due to different nutrient dosages of treatments) reached the deeper soil layers.

After the termination of the long-term experiment the plant nutrition experiment has been turned into an environmental protection one. In this environmental protection experiment our main aim is to dissolve and remediate these previous contaminations caused by intensive fertilization. At the first step we used alfalfa (Medicago sativa L.), that has a rather deep root zone, as test plant. During the production of alfalfa we realized, that the nitrate content of upper soil layers showed a decreasing tendency. For the re-cultivation of the deeper soil layers we planted energy wood – acacia (Robinia pseudoacacia L.) – after the first four year period.

Before and ten years after the plantation we measured the nitrate content of the soil profile each 20 centimetres till a depth of 3 metres. Measuring the nitrate content of the samples taken before the plantation from plots treated with higher fertilizer dosages we realized a significant nitrate accumulation in the layer deeper than 2 metres. Regarding the samples from 10 years later it can be stated, that this accumulation disappeared, or diffused to the upper layers due to the activity of nitrogen binding bacteria in the root tubers of pulses. Therefore the total nitrogen amount did not change, still the loading for the environment ceased. In addition, the heterogeneity between the plots treated with different fertilizer dosages also disappeared. This effect could be detected by modern precision remote sensing methods as well.