NITRATE TRANSPORT IN SOILS OF A RIVER FLO OD-PLAIN UNDER ORGANIC AND CONVENTIONAL FARMING - ANALYTICAL RESULTS, MODELING AND BALANCES

Over a period od two years the transport of nitrate was investigated i n Fluvi-Eutric Cambisols of a river flood plain of the Rhine tributary Sieg (Nordrhein-Westfalen, Germany). The soils were cultivated accord ing to organic and conventional farming systems. Time series of NO3 co ncentrations in soil solutions sampled by ceramic cups down to a depth of 180 cm are given. The interpretation of the results was possible b y model calculations using the model DELPHI, which had been calibrated before by tracer experiments. N-mineralization and N-leaching were qu antified. For different crop residues reaction coefficients for the mi neralization of the easily decomposed organic material were calculated . They were extremely high for bean residues (19.0 10(12) * exp (-98 00/T) and mustard-vetch residues (12.0 10(12) * exp (-9800/T). The l owest reaction coefficient of 3.0 10(12) * exp (-9800>T) was calcula ted for the decomposition process during winter time. For the two farm ing systems a detailed N-balance was calculated. It is shown that unde r conventional farming over a time period of two years 199 kg N/ha wer e leached. Within the same period 53 kg N/ha were leached under organi c farming. These differences depend in part on different crop rotation . Especially intercropping on the organically cultivated plots reduced the leaching of nitrate.