Changes in soil fertility under partial organic substitution of chemical fertilizer: a 33-year trial.

BACKGROUND: This study examined the changes in soil fertility in a maize cropping area when chemical fertilizer was partially replaced with straw or livestock manure over a 33-year period. Four treatments were included: (i) CK (no fertilizer application); (ii) NPK (only chemical fertilizer application); (iii) NPKM (chemical fertilizer partly replaced with livestock manure); (iv) NPKS (chemical fertilizer partly replaced with straw). RESULTS: Soil organic carbon increased by 41.7% and 95.5% in the NPKS and NPKM treatments, respectively, over the 33-year trial compared with the initial concentration. However, soil organic carbon in NPK was significantly reduced by 9.8%. Soil total N, P and K increased in both NPKM and NPKS treatments compared to the original soil. Soil pH was significantly acidified from 7.6 to 5.97 in the NPK treatment during the experimental period. The NPKM and NPKS treatments buffered the acidification compared to NPK. Meta-analysis results showed that, compared with NPK, NPKM significantly raised soil bacteria and fungi populations by 38.7% and 58.6%; enhanced microbial biomass carbon and nitrogen by 66.3% and 63%, respectively; and increased sucrase, urease and catalase activities by 34.2%, 48.2% and 21.5%. NPKS significantly increased soil fungi and actinomycetes populations by 24.3% and 41.2%, respectively; enhanced microbial biomass carbon and nitrogen by 27.1% and 45%; and strengthened sucrase and urease activities by 36% and 20.3%, respectively. CONCLUSION: Long-term chemical fertilizer application led to the deterioration of soil fertility and environment. Partial replacement of chemical fertilizers with organic materials could significantly amend and buffer such negative effects. © 2023 Society of Chemical Industry.