N-fluxes and efficiencies on farms in Styria, Austria

N-fluxes and efficiencies were investigated on three typical pig farms of the Leibnitzer Feld, Styria, Austria. The farms ranged from 26 to 30 ha in size and had 100–200 fattening pigs and 25 brood-sows. Fattening was mainly based on maize and purchased soycake. The N-budget (= sum of all N-inputs = sum of all N outputs) of the farms were similar in relation to Austrian livestock units, DGVE, (146 kg N DGVE−1 year−1 to 162 kg N DGVE−1 year−1) and averaged 181 kg N ha−1 year−1 to 240 kg N ha−1. 43−54% of the total N-inputs were due to fertiliser-N, 28–40% to food-purchase, and 12–17% to atmospheric deposition. 9–23% of the total N-outputs were for sold plant products, 11–16% for sold pigs and 24–33% for ammonia emissions from pig-housing and slurry storage. The rest, remaining in the soil, was 37–57%. Additional investigations with field lysimeters showed that almost all of it was washed out as NO3−. The N-efficiency of plant production as determined on the farms was 59%, animal production had an N-efficiency of up to 25%. 44%–67% of all N excreted by the pigs was lost through NH3-emissions from housing and slurry storage. Comparative investigations on the key components of the farms, maize cropping and pig fattening, were undertaken in order to find out, if changing the N-inputs would improve their N-efficiency and reduce N-losses. For maize cropping a relation of decreasing N-efficiency for increasing N-inputs was determined. Additionally it was found that for a given amount of yield (which was supposed to be necessary for the existing livestock) a small increase of the cultivated area would result in a considerable decrease of the unused fertiliser-N. For pig fattening a reduction of the protein content of the feed would reduce the N-excretions in absolute figures, but the N-efficiency would decrease.