Effects of nitrification inhibitor/microbial inoculum on nitrogen fate in soil-vegetable system of greenhouse

Objectives We assessed the fate of soil nitrogen under single application and combined application of nitrification inhibitors and microbial inoculum in a greenhouse eggplant production system.

Methods The experimental field was set up with a randomized block design and 6 treatments, including no nitrogen fertilizer (CK), conventional nitrogen application of 720 kg/hm² (FN), 30% reduction of nitrogen fertilizer (N 504 kg/hm², RN), 30% reduction of nitrogen combined with nitrification inhibitor (RND), microbial inoculum (RNB) and simultaneous application of nitrification inhibitor and microbial inoculum (RNDB). The nitrogen uptake and utilization, NO₃^–-N accumulation in soil profile, N₂O emission, gaseous loss of NH₃ volatilization and the proportion of each destination in the soil greenhouse eggplant system were assessed.

Results 1) The yield of RNDB treatment was 112.27 t/hm², which was 11.0% higher than that of RND treatment. The soluble sugar content of RNDB was 0.95%, which was significantly higher than that of RND and RNB by 17.3% and 18.8% respectively. 2) The order of nitrogen uptake in all the treatments was: fruit>stem>leaf >root. The total nitrogen uptake of RNDB treatment was 259.66 kg/hm², which was 16.1% higher than that of RN. The apparent nitrogen use efficiency of RNDB treatment was the highest (20.87%), which was not significantly different from RND and RNB treatment. The agronomic efficiency of nitrogen fertilizer was 99.69 kg/kg, which was only significantly higher than that of RND treatment. 3) Under the same nitrogen application rate, the net gaseous loss (N₂O and NH₃) and net loss rate in RNDB treatment were 16.05 kg/hm² and 4.73% respectively. The accumulative N₂O emission of RNDB was significantly lower than that of RNB by 28.8%. There was no significant difference in NH₃ volatilization accumulation among treatments. 4) The accumulation of NO₃^–-N in 0–60 cm soil profile was FN> RNB>RN>RND>RNDB>CK. Except in CK treatment, the lowest accumulation of RNDB treatment was 873.1 kg/hm². The accumulation of soil NO₃^–-N in RNDB treatment was 17.6%, 17.7% and 2.2% lower than that in RN, RNB and RNDB treatment, respectively. The accumulation of NO₃^–-N in 60–120 cm soil profile was FN> RN > RNB>RND>RNDB>CK. The NO₃^–-N accumulative amount of RNDB treatment was 744.0 kg/hm², which was 1.0% and 25.2% lower than that of RND and RNB treatment, respectively.

Conclusions Reducing nitrogen by 30% combined with nitrification inhibitor and microbial inoculum application could effectively reduce N₂O and NH₃ gaseous loss, improve nitrogen absorption of eggplant and significantly reduce nitrogen residue in 0–60 cm soil profile. It is an effective measure to realize environment-friendly production of high quality and high yield eggplant.