Growth stage-specific application of slurry and mineral N to oilseed rape, wheat and barley

Farmers commonly apply slurry when soil conditions are suitable for spreading. In order to improve slurry nitrogen (N) use efficiency, effects of split application of pig slurry according to the crop N demand on yield were tested in 1994/95–2001/02. The crop rotation was winter oilseed rape (OSR) – winter wheat – winter barley. N was applied as pig slurry or as mineral N fertilizer (each of 0, 40 or 80 kg N/ha, total N amount: 0–240 kg N/ha) at three dates. Each year, the treatments occurred in all three crops of the rotation and were located on the same plots. On average, mineral N fertilizer led to higher grain yields in all crops (+0·33 t/ha in OSR, +0·57 t/ha in wheat, and +0·20 t/ha in barley) compared with slurry application, presumably due to a slower N mineralization of the organic fraction. However, the large year to year variation resulted in high error estimates, leading to no significant differences in yield. Taking only the ammonium amount of the slurry into account, there was no significant difference in yield between the two N sources. Yield potential was similar in both slurry and mineral N treatments, but higher N amounts were necessary on the slurry plots. Therefore, slurry N-use efficiency (NUE) remained lower than that of mineral N. However, compared with a single dose, growth-specific slurry application according to the crop demand, as made with mineral N fertilizers, increased NUE.