PLANT AVAILABLE ORGANIC NITROGEN, EUF-NORG AND ITS RELEVANCE FOR ENVIRONMENTALLY COMPATIBLE FARMING .2. INFLUENCE OF ORGANIC-N SUPPLY ON THE EUF NITROGEN FRACTIONS OF ARABLE SOILS

The influence of different farm management systems (different N supply to the soil) was investigated in 216 farms. The following groups of management systems were involved: 1. farms without organic manuring 2. farms with organic manuring a) solid manure b) slurry (cattle and pig slurry) 3. farms with vegetable production (irrigation) 4. farms with vegetable production on sandy soils (irrigation) The highest mean SIGMA-EUF N content of 4.2 mg@100 g was found in farms with vegetable production followed by farms applying slurry with a mean of 3.6 mg. Both farms without organic manuring and farms with application of solid manure had an average SIGNA-EUF N content of 2.8 mg. The lowest N values were found in the irrigated sandy soils averaging at 2.1 mg. Pig slurry raised the EUF N contents more than cattle slurry. The EUF N determinations were therefore able to reflect the different management systems of the 216 farms. The same was true for the alpha-Amino-N-values of sugar beets of the different management systems. The highest alpha-Amino-N values were found together with the highest EUF-N(org)-contents and the highest EUF-N(org)-Quotient values. The EUF N(org) contents only increased by application of pig slurry. It is shown that the often very high N supply of farms using pig slurry can also be characterized by higher EUF N(org) contents and higher EUF N(org) quotients.