Different Accumulation Patterns of Copper in Soils and Plants After 43-Year Nitrogen and Manure Fertilization

Copper (Cu) is an essential nutrient for plants. Fertilizer application is a key factor influencing the migration and transformation of Cu in the soil-plant system. However, limited studies have assessed the distribution, speciation, and transformation of Cu as well as its bioavailability under long-term fertilization conditions. In this study, we investigated the distribution and enrichment pattern of Cu in bulk soil and aggregates based on a 43-year long-term fertilization experiment on brown soil. The results present that long-term N fertilizer application can maintain total soil Cu at a stable level across the monitored 43 years, simultaneously increasing the Ws-Cu and Ca-Cu, thus increasing the Cu contents in maize and soybean. While long-term manure fertilizer application significantly enhanced Cu accumulation and availability in soil in terms of total Cu and various Cu fractions, Cu content declined in maize and soybean. The combined application of N fertilizer and manure fertilizer led to further accumulation of total Cu, DTPA-Cu, Ca-Cu, Ox-Cu, and Or-Cu, as well as Cu in 1–2 mm and 0.5–1 mm aggregates, but resulted in a decrease in Cu content in the 0.25–0.5 mm, 0.053–0.25 mm and <0.053 mm aggregates only under M2 treatments. In addition, the combined use of N fertilizer and manure fertilizer mitigated the reduction in plant Cu content caused by sole manure application. These findings provide a scientific basis for regulating Cu transport and transformation in the soil-plant system via combined organicinorganic fertilization in agricultural production.