Opportunities to improve nitrogen use efficiency in an intensive vegetable system without compromising yield

Intensive vegetable cropping systems rely heavily on nitrogen (N) inputs from multiple synthetic and organic fertilizer applications. The majority of applied N is lost to the environment through numerous pathways, including as nitrous oxide (N₂ O). A field trial was conducted to examine the opportunities to reduce N input in an intensive vegetable system without compromising yield. Treatments applied were control (no N), manure (M, 408 kg N ha^-1 from chicken manure), grower practice (GP, 408 kg N ha^-1 from chicken manure + 195 kg N ha^-1 from fertilizer), and 2/3 GP (two-thirds of the total N input in GP), all with and without 3,4-dimethylpyrazole phosphate (DMPP). Nitrogen recovery in the GP treatment was determined using ¹⁵ N-labeled fertilizer. Using only manure significantly lowered celery (Apium graveolens L.) yield and apparent N use efficiency (ANUE) compared with GP. Reducing N input by one-third did not affect yield or ANUE. Use of DMPP increased ANUE despite no yield improvement. More than 50% of the applied N in the GP treatment was lost to the environment, with almost 10 kg N ha^-1 emitted as N₂ O over the season, which was 67 times more than from the control. Reducing the N input by one-third or using manure only reduced N₂ O emissions by more than 70% relative to GP. This study shows that there is a clear opportunity to reduce N input and N₂ O emissions in high-fertilizer-input vegetable systems without compromising vegetable yield.