Effect of Urease Inhibitors and Nitrification Inhibitors Combined with Seaweed Extracts on Urea Nitrogen Regulation and Application

In order to improve the application effect of inhibitors, the combination of seaweed extracts (SE), urease inhibitors (UIs) and nitrification inhibitors (NIs) were added to urea fertilizers for providing a theoretical basis to develop the efficient stabilized nitrogen (N) fertilizer. The combinations were tested in outdoor pots with no N fertilizer (CK) and application of urea alone (U) as control, and SE, N−butyl phosphorothioate triamine (NBPT), 3,4−dimethylpyrazole phosphate (DMPP), 2−chloro−6−trimethylpyridine (CP), and combinations of SE with each of the three inhibitors were added to urea to make seven fertilizer prototypes. The results showed that the addition of inhibitors and SE could regulate the N transformation, enzyme activity and microbial biomass carbon (MBC) contents and significantly improve maize yield and N use efficiency (NUE) (p < 0.05). Compared with the addition of inhibitor alone, the addition of SE was beneficial to N uptake by plants at the early growth stage of maize, but reduced the inhibitors effect; DMPP + S significantly increased the maize total biomass and NUE (p < 0.05), and the grain yield, N uptake and NUE by 15.6%, 28.5% and 30.6%, respectively. Therefore, the addition of DMPP with SE to urea significantly improved yield when planting maize in loess areas.