Abstract: Understanding the effects of urea addition with humic acid and biochemical inhibitors in rice cultivation in loess can provide a theoretical basis for developing new types of high-efficiency and stable urea fertilizer for loess rice paddy field. In a pot experiment, blank (CK) and urea (N) were set as controls, and humic acid (H), N-butyl thiophosphate-triamine (NBPT), 3,4-dimethyl-pyrazolate phosphate (DMPP), 2vchloro-6-trimethyl-pyridine (CP), and humic acid combined respectively with three biochemical inhibitors were added into urea to form seven types of fertilizers. Compared with the application of urea alone, the addition of humic acid inhibited soil nitrification, promoted rice growth, and significantly increased grain yield by 13.3% and grain N uptake by 21.7%, with an increased nitrogen use efficiency (NUE) (P<0.05). Addition of humic acid with NBPT did not affect the transformation characteristics of urea nitrogen compared with NBPT alone, but significantly increased total N uptake and NUE by 8.0% and 9.3%, respectively. Compared with the DMPP treatment, the addition of humic acid inhibited soil nitrification in the early growth stage and significantly increased the total biomass of rice by 7.3%. Compared with the CP treatment, the addition of humic acid inhibited soil nitrification, but significantly decreased grain yield, partial factor productivity and agronomic efficiency of applied nitrogen by 11.3%, 11.3%, and 13.2% (P<0.05), respectively. Our results suggest that the combination of humic acid and DMPP should be the first choice for developing new type of high-efficiency and stable urea fertilizer for rice cultivation in loess areas, followed by NBPT + humic acid. The combination of CP and humic acid had negative effects, which was less effective than adding CP alone.

Key words: rice, biostimulant, urease inhibitor, nitrification inhibitor, nitrogen use efficiency.