Based on the long-term fertilization station in fluvo-aquic soil region, this study investigated how bacterial community structure, ecological network, and key species in response to fertilization.

Based on the long-term experiment started from 1990, soil was sampled after wheat maturity in 2023, and high-throughput sequencing and ecological network analysis were used to examine dynamics in soil organic carbon (SOC) and other nutrients, enzyme activity, bacterial community composition, ecological network and stochastic process under four treatments: no fertilization (CK), mineral nitrogen (N), phosphorus (P), and potassium (K) (NPK), NPK+straw (NPKS), and NPK+manure (NPKM).

The combined application of organic and inorganic fertilizers significantly increased SOC and other soil nutrients, as well as soil enzyme activity. Compared with CK, SOC content under NPKS and NPKM increased by 52.1% and 81.9%, respectively, and particulate carbon increased by 60.6% and 137.4%, respectively, and easily oxidized organic carbon increased by 45.3% and 63.4%, respectively; additionally, β-N-acetylglucosaminidase activity increased by 7.2% and 12.6%, respectively, while alkaline phosphatase activity increased by 166.4% and 216.2% (P<0.05), respectively. Notably, β-1,4-glucosidase activity was the highest under NPKS (63.82 μmol·g^-1·d^-1). In terms of bacterial diversity, α-diversity significantly decreased under NPKS compared with CK, with reductions of 5.4%, 5.2%, and 2.6% in the Ace, Chao1, and Shannon indices, respectively (P<0.05). Fertilization treatment alerted bacterial community structure, while NPKS and NPKM exhibited similar compositions. Compared with CK, NPKS significantly reduced the relative abundance of Chloroflexi, Gemmatimonadota, and Methylomirabilota, while NPKM significantly increased the relative abundance of Bacteroidota (P<0.05). Redundancy analysis identified ammonium nitrogen (NH₄⁺-N), nitrate nitrogen (NO₃^--N), and organic carbon (SOC) as the primary environmental factors shaping microbial community structure. Network analysis showed, compared with CK, NPKM increased the complexity, stability of the bacterial community network and the proportion of positive correlations between species. Furthermore, both NPKS and NPKM significantly enhanced the relative abundances of eight keystone taxa, including members of Actinobacteriota (order Microtrichales), Chloroflexi (order Thermomicrobiales), Bacteroidota (orders Chitinophagales and Cytophagales), Myxococcota (uncultured order bacteriap25), and Proteobacteria (order Burkholderiales) (P<0.05). These keystone taxa were closely associated with soil carbon, nitrogen, phosphorus, and other material cycling, as well as plant growth promotion. Partial least squares path modeling suggested that fertilization did not directly impact key species but exerted an indirect influence by significantly affecting soil pH, regulating community composition, and increasing soil nutrient availability.

Long-term combined application of organic and inorganic fertilizers enhanced soil nutrient content and extracellular enzyme activity, regulated microbial community composition and structure, affected bacterial network complexity and stability, and increased the relative abundance of key species involved in soil nutrient cycling and material transformation. These findings provided valuable insights into the interactions between soil properties and microbial communities under long-term fertilization, contributing to a deeper understanding of bacterial community dynamics and key species in agricultural ecosystems.

Based on the long-term rotation experiment, this study explored the characteristics of ammonia volatilization and crop yield change in Fluvo-aquic soil.

The long-term experiment started in 2016, and this study carried out 2023-2024. A randomized block design with five crop rotation treatments were set as: (1) continuous wheat-maize (WMWM); (2) continuous wheat-peanut (WPWP); (3) continuous wheat-soybean (WSWS); (4) 1-year wheat-maize + 1-year wheat-soybean (WMWS); (5) 1-year wheat-maize + 1-year wheat-summer peanut (WMWP). The ammonia volatilization rate (AVR) and cumulative volatilization (ACV), the content of different nitrogen forms in soil, nitrogen content in crop, and crop yield were measured and analyzed.

The ACV in summer-autumn season was higher than that in wheat season, and the AVR in both seasons concentrated in 1st-9th day after fertilization. Under the same fertilization condition, at the summer-autumn season, the AVR peak in WMWM treatment was the highest one with 4.15 kg·hm^-2·d^-1. At the wheat season, the lowest AVR of wheat base fertilizer was observed under WMWS (0.77 kg·hm^-2·d^-1), and the lowest AVR after topdressing fertilizer was under WSWS (0.40 kg·hm^-2·d^-1). The lowest ACV was under WMWP and WMWS during both summer-autumn and wheat seasons, which decreased by 18.7% and 14.8%, 12.5% and 28.6%, respectively, compared with WMWM. In the 0-20 cm soil layer, the content of ammonium, nitrate, and total nitrogen under WPWP and WSWS were significantly higher than those under WMWM during the two seasons. Compared with WMWM, the content of nitrogen in wheat grains under WPWP and WSWS were increased by 12.9% and 17.2%, respectively, and the similar trend was observed in grain nitrogen accumulation, with 135 kg·hm^-2 and 137 kg·hm^-2, respectively. The maize equivalent yield (MEY equal to price yield) under WPWP treatment was significantly higher than other treatments, which was 41.7% higher than that under WMWM treatment. Compare with WMWM, the panicle number (7.0% and 3.5%), kernel number per spike (20.7% and 15.9%), thousand grain weight (5.4% and 4.1%) and yield (10.8% and 10.9%) were enhanced under WPWP and WSWS treatment. During the whole rotation cycle, crops absorbed nitrogen accounted for 43.8%-56.3%, and ammonia volatilization accounted for 1.9%-4.5%. The highest crop absorbed proportion was under WMWP, while the lowest proportion ammonia volatilization was under WSWS.

In the Fluvo-aquic soil area of northern Henan Province, the rotation of wheat and legume crops improved the soil nutrient, reduced the soil ammonia volatilization, increased the nitrogen content and wheat yield, which was recommended as a suitable rotation mode in this area.