Abstract: Understanding the effects of potassium and trace element application on soil ecological functions and soil health in farmland can provide theoretical basis for soil nutrition management. In this study, we examined the impacts of potassium and trace element addition on soil ecological function and health in farmland with long-term application of nitrogen and phosphorus fertilizer in Changwu Agricultural Ecological Experimental Station, Chinese Academy of Sciences. There were six treatments, a control without potassium and trace elements (CK), K addition (30 kg·hm^-2 of potassium chloride), Cu addition (15 kg·hm^-2 of copper sulfate), B addition (11.25 kg·hm^-2 of borax), Mn addition (22.5 kg·hm^-2 of manganese sulfate), and Zn addition (15 kg·hm^-2 of zinc sulfate). We collected soil samples of 0-20 cm layer to analyze the soil physical and chemical properties and microbial acti-vity indicators, constructed the minimum data set and calculated the soil health index. The results showed that K addition significantly increased soil available phosphorus content by 27.2%, increased alkaline phosphatase activity by 52.2%, and improved the bioavailability of soil phosphorus. The addition of Cu significantly increased soil respiration by 40.8% and N-acetylglucosamine enzyme activity by 63.6%, enhancing soil carbon and nitrogen conversion. The content of total phospholipid fatty acids, bacterial phospholipid fatty acids, and anaerobic phospholipid fatty acids was increased by 8.5%, 7.2%, and 12.3%, respectively, and microbial biomass carbon and nitrogen contents were promoted. The addition of Zn and B significantly reduced the biomass of bacteria, arbuscular mycorrhizal fungi, Gram positive bacteria, Gram negative bacteria, and actinomycetes by 35.3%, 32.2%, 31.5%, 40.1%, 34.5%, and 22.6%, 26.4%, 20.5%, 23.9%, and 22.6%, respectively, and reduced soil respiration. The addition of Mn significantly increased soil β -1,4-glucosidase activity (45.6%), but reduced the biomass of bacteria, arbuscular mycorrhizal fungi, Gram positive bacteria, Gram negative bacteria, actinomycetes, and soil respiration. The soil health index of each treatment was as follows: K(0.94)>Cu(0.80)>CK(0.78)>B(0.75)=Mn(0.75)>Zn(0.71). In summary, K and Cu addition to farmland soil in the Loess Plateau would be beneficial for the health and stability of soil ecosystems.

Key words: farmland ecosystem, trace element, soil ecological function, soil health index