Vergleich der pflanzenbaulichen Systemwirkungen vergorener und unvergorener Wirtschaftsdünger und Vergärung von pflanzlichen Koppelprodukten in einem Betriebssystem der ökologischen Landwirtschaft mit Viehhaltung

Summary

The influence of biogas production in organic farming systems on different agricultural aspects is being researched in a field trial on the research station Gladbacherhof of the University of Giessen. The investigations took place within a whole crop rotation including 7 different crops in 8 years: two years clover grass followed by winter wheat, potatoes, rye, peas, spelt and at last summer wheat with undersown clover grass. Intercrops were sown after winter cereals and peas. This crop rotation is able to feed an average livestock husbandry in organic farming (0.8 cows ha-1). Four different fertilizing systems are being compared: 1) solid manure ploughed under before seeding of crops, 2) slurry spread out in emerging winter cereals or ploughed under to summer crops, 20 % were applied to mustard-vetches catch crop 3) fermented slurry applied like system 2 and 4) fermented slurry plus fermentation of crop residues and catch crops. The systems with slurry have a slurry storage capacity of half a year. Fermentation takes place in two biogas reactors, one for slurry (fully mixed reactor) and another one for plant residues (percolation system).
Total N efficiencies of manure and slurry fertilizing systems are comparable. Reasons for this are: a) the atmospheric nitrogen losses after spreading out slurry on the surface of the soil and b) the reduced biological N2 fixation by vetches after application of slurry before seeding due to the limitations in storage capacity.
Fermentation of crop residues and catch crops increases to about 70 % the mobile fertiliser pool but the productivity of the whole system is not higher, because a) about 50 % of N is within the solid phase of fermentation residue with a wide C/N ratio (≈19) and b) harvest and storage of crop residues and catch crops decreases the N-loss potential in winter (NO3, N2O), but other losses related to harvest, storage and mainly to spreading back on the soil in spring time are affecting the N use efficiency of the system.