The Huangpu River, a source of drinking water, has been highly contaminated in recent years by fertilizer-rich agricultural drainage from extensive fertilizer uses in vegetable farms for high yields in the suburbs of Shanghai. A fertilizer-use reduction experiment (between 20 and 40%), in combination with a newly composed mixture of two lad-developed microbial inoculant strains, was used to analyze spinach growth characteristics and soil microbial population in cultivated lands of Shanghai suburbs. The aim of the experiments was to investigate the characteristics of spinach and soil microbial environment under reduced fertilizer use, augmented with patent microbial agents.

Results showed that reduced fertilization was conducive for improving the chlorophyll content and fluorescence parameters of spinach. Compared with T1 (100% chemical fertilizer), the combined treatments of reduced chemical fertilizer and inoculants presented higher chlorophyll content and fluorescence parameters of spinach at the later growth stage but lower at latter stages. The results showed that the nitrate content of the edible parts of spinach was highest under CK (without fertilizer) treatment, while those of treatments with inoculants were significantly reduced. The absorption and use efficiency of N, P and K were highest under 20% fertilizer reduction with 100% inoculant treatment. Spinach yield was increased under combined treatments of reduced fertilizer and inoculant. Spinach yield under 40% fertilizer reduction with 100% inoculant was the highest (approximately 227.73 g·pot^-1), an increase of 170% compared with the control treatment. Microbial richness index (from extracting total microbial DNA via PCR-DGGE and analyzing soil microbial diversity) was lowest in chemical fertilization treatment, while Shannon-Wierner index was 0.398, lower than that under CK treatment. Shannon-Wierner indexes under inoculant treatments were 0.547-0.983.

The results suggested that microbial inoculants improved spinach yield, NPK uptake and use efficiency and soil microbial diversity. The combined application of 100% microbial inoculants with 40% reduction of chemical fertilizer significantly promoted spinach growth.