Abstract: Application of fertilizer has been found to significantly affect soil N cycling.  However, a comprehensive understanding of the effects of long-term fertilization on soil gross N transformation rates is still lacking.  We compiled data of observations from 10 long-term fertilization experiments and conducted a meta-analysis of the effects of long-term fertilization on soil gross N transformation rates.  The results showed that if chemical fertilizers of N, P and K were applied in balance, soil pH decreased very slightly.  There was a significantly positive effect of long-term fertilization, either chemical or organic fertilizers or their combinations, on gross N mineralization rate compared to the control treatment (the mean effect size ranged from 1.21 to 1.25 at 95% confidence intervals (CI) with a mean of 1.23), mainly due to the increasing soil total N content.  The long-term application of organic fertilizer alone and combining organic and chemical fertilizer could increase the mineralization-immobilization turnover, thus enhance available N for plant while reduce N losses potential compared to the control treatment.  However, long-term chemical fertilizer application did not significantly affect the gross NH4+ immobilization rate, but accelerated gross nitrification rate (1.19; 95% CI: 1.08 to 1.31).  Thus, long-term chemical fertilizer alone would probably induce higher N losses potential through NO3– leaching and runoff than organic fertilizer application compared to the control treatment.  Therefore, in the view of the effects of long-term fertilization on gross N transformation rates, it also supports that organic fertilizer alone or combination of organic and chemical fertilizer could not only improve crop yield, but also increase soil fertility and reduce the N losses potential.

Key words: chemical fertilizer ,  organic fertilizer ,  gross N transformation rate ,  long-term fertilization experiment ,  meta-analysis