Short-term effects of biogas residue application on yield performance and N balance parameters of maize in different cropping systems

The expansion of biogas production in Germany poses a challenge in terms of the production of substrates for co-fermentation and the efficient use of biogas residues as fertilizers. At present there is limited information on the fertilizer value of biogas residues from energy-cropping systems. A 2-year field experiment was conducted at two sites in northern Germany to quantify the yield, nitrogen (N) concentration and the N balance of maize (Zea mays L.) grown in different crop rotations: (i) maize monoculture (R1), (ii) maize - whole-crop wheat followed by Italian ryegrass as catch crop (R2) and (iii) maize - grain wheat followed by mustard as catch crop (R3). Crops were fertilized with different levels of biogas residues, cattle slurry, pig slurry, or mineral N fertilizer, which allowed quantification of the apparent N recovery (ANR) of the fertilizer types tested. The results revealed that crop rotation in interaction with N amount had a pronounced effect on the yield of maize. Maximum yield of 19.1 t dry matter (DM)/ha, corresponding to biogas production of 6685 m(N)(3) CH4/ha, was achieved in maize monoculture on a sandy loam site. Maize grown in R3 showed the lowest N response but had the highest yield under low N supply, whereas R2 generally had the lowest yield and N content. Differences in yield performance were reflected in the N balances, differing by 50 kg N/ha between R1 and R2, whereas R3 produced the lowest yield at low N supply. The carry-over effects from the preceding catch crops in R2 and R3, however, reduce the meaningfulness of the simple N balance. Nitrogen fertilizer type showed no interaction with crop rotation. Biogas residue application resulted in similar maize yielding performance to pig slurry and cattle slurry. However, relative N fertilizer value (RNFV) was 30% higher for biogas residue at optimal N supply, i.e. the minimum N input to achieve maximum DM yield.