Combining N-inhibitor and chicken manure with reduced N fertilizer to improve the conversion and utilization of fertilizer N in a paddy soil

Objectives The nitrogen supply and utilization of soil and fertilizer-derived N were studied under the condition of reduced urea N input and combined with N-inhibitors and chicken manure, to provide a theoretical basis for rice cultivation in Northeast of China, in terms of improving the nitrogen use and fertilizer efficiencies.

Methods ¹⁵N isotope tracer technology was adopted in a rice pot experiment. The five treatments included: no nitrogen fertilizer control (CK), conventional rate of urea (urea-¹⁵N), 80% urea N + 20% chicken manure N (NM), 80% urea N+ inhibitor (NI), 80% urea N + inhibitor + 20% chicken manure N (NIM). The contents of ammonia nitrogen and microbial biomass N in soil and urea-derived nitrogen, and nitrogen content of rice plant at different growth stages were analyzed, investigated the rice yield was investigated.

Results 1) NI treatments had considerable soil ammonium N and fertilizer derived N supply ability compared with N treatment, inhibitors had a compensatory effect on nitrogen reduction. NM treatment had markedly higher N supply ability at the tillering and filling stages, compared to N treatment. Compared with N treatment, soil NH₄⁺-N in NIM treatment increased by 19.2%, 66.3%, and 36.5%; NO₃⁻-N content increased by 13.9%, 12.7%, and 17.3% at returning green, tillering and filling stage, respectively, ¹⁵NH₄⁺-N content increased by 14.59 mg/kg at tillering stage. 2) N and NI treatments had no significant effect on soil microbial biomass carbon (MBC) content, however, NM and NIM treatments significantly improved soil microbial biomass N (MBN) content at the returning green and filling stage (P < 0.05). Compared with N treatment, the MBC content in NIM treatment increased by 32.61%, 29.23%, 53.46% and 2.85%, and the MBN content increased by 147.98%, 22.97%, 133.33% and 24.63% at the returning green, tillering, filling and mature stages, respectively, while ¹⁵N-MBN increased by 22.56 mg/kg at the tillering stage. 3) N-inhibitor with chicken manure addition increased the rice yield and biomass. Compared with N treatment, NIM increased the biomass, yield and nitrogen uptake of rice by 83.59%, 124.18% and 46.66%. It also significantly increased fertilizer N residue in the soil by 56.48% and reduced the fertilizer N loss by 78.7%. Compared with N treatment, NIM treatment had a significant effect on N absorption and utilization of fertilizer, and its N absorption, N utilization rate and N agronomic efficiency were significantly higher than other treatments.

Conclusions For brown paddy soil of northern China, the addition of inhibitor (1% PPD+1% NBPT+2% DMPP) and chicken manure could replenish soil N supply. Based on 20% reduction in urea, augments with the application of inhibitors and chicken manure increased the fertilizer utilization rate and increased the rice yield. From the perspectives of fertilizer N release and utilization in rice, NI and NIM treatments shows superior agronomic performances.