Chemical fertilizer reduction with organic fertilizer effectively improve soil fertility and microbial community from newly cultivated land in the Loess Plateau of China

Improving the soil quality of cultivated land generated by the Gully Land Consolidation Project could promote sustainable economic and ecological development in the hilly gully area of the Loess Plateau, China. A pot experiment with maize crop was conducted to assess the effects of different organic amendments and chemical fertilizer reduction on soil fertility and the microbial community in newly cultivated land, of which the amount of chemical fertilizer applied was half of the local conventional maize field (90 kg ha−1 of CO(NH2)2, 45 kg ha−1 of P2O5, and 60 kg ha−1 of K2O). The experiment involved six treatments: bare soil (CK), only maize (M), maize + chemical fertilizer (MF), maize + chemical fertilizer + organic fertilizer (MFO), maize + chemical fertilizer + biochar (MFB), and maize + chemical fertilizer + polyacrylamide (MFP). The results are as follows: (1) compared with the MF treatment, the MFO treatment exhibited the best effect on improving soil physicochemical properties, such as electrical conductivity (EC), soil organic carbon (SOC), nitrate nitrogen (NO3−-N), total nitrogen (TN), available phosphorus (AP) and available potassium (AK), followed by MFB and MFP. (2) The MFO treatment significantly (P < 0.05) improved the Species richness and Shannon indices of the bacteria, but its effects on fungal diversity index are not significant. (3) The MFO treatment increased the relative abundance of Betaproteobacteria, Alphaproteobacteria, Gammaproteobacteria and Gemmatimonadetes and decreased the relative abundance of Sordariomycetes and Agaricomycetes, and it also increased the functional abundance of Amino acid metabolism, Membrane transport, Xenobiotics biodegradation and metabolism, Undefined Saprotrophs and Arbuscular Mycorrhizal Fungi. (4) The TN and EC were the main driving factors of bacterial community structural variation, while TN and NO3−-N were the main factors for variation of fungal community structure. (5) The fresh weight and dry weight of maize increased significantly (P < 0.05) under all amendment treatments, among which the MFO treatment had the greatest effect. In conclusion, organic fertilizer application is the most effective measure for rapidly improving soil fertility and microbial community structure. Our findings have valuable implications for agricultural land productivity, food security and long-term sustainability of the environment.