Objectives Soil amendments are frequently employed to enhance the micro - environmental conditions and accelerate the mineralization rates of organic matter. By doing so, they furnish crops with an efficient nutrient supply and foster a conducive environment for healthy growth. In this study, we conducted a comparative analysis to assess the impact of the long - term application of soil amendments and microbial agents on soil nitrogen availability and crop growth within a continuously cropped system. The ultimate aim is to formulate appropriate soil management strategies tailored for economically significant continuous cropping systems.

Methods A positioning experiment was carried out in the Base for Soil Fertilizer of National Peanut Industry Technology System of Shenyang Agricultural University since 2011. The four treatments were: maize-peanut rotation (MPR), peanut continuous cropping (PC), peanut continuous cropping applied with amendments (PCCA) and microbial agent (PCBA). All the treatments were basal applied with N 60 kg/hm², P₂O₅ 82.5 kg/hm² and K₂O 112.5 kg/hm². Soil samples were collected during the seedling, flowering and needing, podding, and maturity stages of peanut in 2023 for nitrogen mineralization incubation tests, and the determination of soil inorganic N, organic nitrogen fractions, microbial biomass nitrogen (MBN), and fixed ammonium (FN). At maturity, plant samples were collected to determine nutrient content, biomass, and peanut yield.

Results Compared with PC, PCCA treatments increased soil NH₄⁺-N by 25.54%−198.57% and NO₃⁻-N by 12.47%−94.82% across all growth stages, increased net nitrogen mineralization rate after 21 days of incubation by 37.5%–43.75%, and the increase by PCCA was significantly higher than that by PCBA. The effects of PCCA and MPR on organic nitrogen fractions depended on the growth stages. Compared to PC, PCCA significantly increased soil acidolysed ammonium nitrogen and acidolysed amino acid nitrogen contents by 7.79%–29.32% and 13.87%–19.02%, respectively, and MPR increased these fractions by 9.15%–32.16% and 12.17%–22.00%, respectively. At maturity, PCCA and MPR significantly increased acidolysed amino sugar nitrogen by 26.16% and 30.77%, and acidolysed unknown nitrogen by 30.65% and 37.84%, respectively, but significantly reduced non-acidolysed nitrogen by 15.50% and 13.38%. The organic nitrogen fractions in MPR were comparable to those in PCCA. PCCA, PCBA, and MPR significantly increased soil MBN and FN by 18.43%–22.28% and 11.58%–22.49% after 21 days of incubation, respectively. PCCA had a more pronounced effect on fixed ammonium relative to MPR.

Conclusions On peanut continuous cropping soil, the application of amendments prepared from biochar and silica powder or crop rotation increased the contents of soil acidolysed ammonium nitrogen and acidolysed amino acid nitrogen, as well as the rate and amount of soil nitrogen mineralization. In the amendment-treated soil, a portion of the inorganic nitrogen formed through mineralization was preserved in the soil in the form of fixed ammonium, enhancing the stability of soil nitrogen supply. As a result, the amendment treatment achieved better effects than crop rotation in increasing the accumulation of N, P, and K in peanut pods and shoots. Microbial agents had no significant impact on soil organic nitrogen fractions, especially acidolysed organic nitrogen fractions. However, they elevated the contents of ammonium nitrogen and nitrate nitrogen in the soil during the peanut seedling stage and the pegging-flowering stage, thereby promoting nutrient supply in the early growth stages of peanuts and also resulting in a significant yield increase. Therefore, the application of both amendments and microbial agents are effective measures to replace crop rotation.