The International Organic Nitrogen Long-term Fertilization Experiment (IOSDV) at Vienna

Abstract

After 15 experimental years the following results from the IOSDV - Vienna in a semiarid region with a three year crop rotation (sugar beet - winter-wheat-winter-barley) are presented. At the medium textured loess site suitable for deep-rooting development, the relative level of output without any fertilizing and manuring reached about 73% of optimal potential, which could be achieved by combined organic and mineral fertilization. Due to irrigation as required especially sugar beets made use from the site specific nitrogen-mineralization potential. With combined organic and mineral fertilization optimal yields were increased by 2-3% compared to optimal mineral fertilizer rates of 122kg N, the corresponding mineral N doses of the organic treatments were reduced by 21-29%. When all crop residues remained at the field - with an additional small mineral N dose for straw rotting - the N-balance at optimal fertilizer input was slightly positive (+21kg N); when all crop residues were removed, especially beet leaves, optimal yields of the organic treatments were realized with negative N-balance results (without organic manure: m 77kg N; 30t stable manure to sugar beet: m 42kg N; 40m 3 cattle slurry to sugar beet and winter barley: m 8kg N). Nt-content of topsoil was significantly influenced due to N-balance results, whereas no distinctive effects on Corg were detected so far. The apparent N-utilization efficiency of the applied organic N increased with continuous duration of the experiment and reached values of 70% from stable manure and of nearly 50% from cattle slurry in the last rotation. The P and K inputs from the organic treatments were recorded slightly in the CAL extracts.