Response of No‐Till Grain Crops to Pig Slurry Application Methods and a Nitrification Inhibitor

CORE IDEAS: Mineral N fertilization of no‐till crops may be replaced by pig slurry. Pig slurry with and without dicyandiamide was injected or broadcast in a no‐till soil. Pig slurry injection in a no‐till soil increased grain yield and crop N use efficiency. Dicyandiamide added to slurry improved crop yield and N use efficiency only in winter crops. The effects of application methods and nitrification inhibitors on the fertilizer value of pig slurry (PS) in no‐till crops are still poorly documented. We evaluated grain and straw yield, and N accumulation of no‐till corn (Zea mays L.), oat (Avena strigosa Schreb.), and wheat (Triticum aestivum L.) from 2011 to 2015 on a loam soil under a subtropical climate. The crops received either: (i) no fertilizer, no dicyandiamide (DCD) (control), (ii) surface‐broadcast of urea‐N (reference treatment), (iii) surface‐broadcast pig slurry (PSs), (iv) PSs + DCD, (v) shallow‐injected pig slurry (PSi), or (vi) PSi + DCD. Broadcast applications were performed manually whereas injection in furrows (≈10 cm) was made with a commercial applicator. Corn and wheat grain yields were similar with pig slurry and mineral fertilizer, confirming the good fertilizer value of pig slurry for no‐till grain crops. Compared with surface broadcast, shallow injection of pig slurry increased grain yields of corn (+1.5 Mg ha⁻¹) and wheat (+0.3 Mg ha⁻¹), nitrogen agronomic efficiency (NAE) of corn (+9 kg grain kg⁻¹ total N applied) and wheat (+2 kg grain kg⁻¹ N), and apparent nitrogen recovery (ANR) in corn (46–68%) and wheat (29–38%). Crop performance was generally not affected by DCD, except for wheat in 2013 with increased yield (+15%), NAE (+2.7 kg grain kg⁻¹ N), and ANR (31–39%). Pig slurry injection improved yield and N use efficiency of no‐till grain crops, whereas DCD addition to pig slurry appeared more favorable for winter than summer crops.