Swine feed is often supplemented with Cu and Zn, but > 90% of the ingested metal is excreted, ultimately accumulating in soil treated with liquid swine manure (LSM) to meet nitrogen (N) requirements. A maize field experiment was conducted between 2002 and 2015 in the Ebro Valley (north-east Spain) to determine the effects of long-term LSM application at two rates [30 and 50 m³ ha⁻¹, equivalent to ~ 220 (218) and ~ 390 (389) kg N ha⁻¹] compared to 0 and 300 kg N ha⁻¹ mineral fertilizer. The highest Cu concentration in plants (5.03 mg kg⁻¹) was observed following the 300 kg N ha⁻¹ treatment. The treatments did not affect plant Zn levels (~ 21 mg kg⁻¹). All whole-plant and grain metal concentrations were lower than threshold values for animal and human ingestion (30 mg Cu kg⁻¹ and 500–1300 mg Zn kg⁻¹). After 12 years, the soil organic carbon (SOC) of 13 g kg⁻¹ in the first year (2002) increased by 19% and 26% at the low and high LSM rates, respectively. Mineral fertilization (300 kg N ha⁻¹) achieved a 22% increase in SOC and also the 0 kg N ha⁻¹ control treatment caused the SOC to rise by 11%. LSM applications do not seem to have adverse effects on maize yields after 12 years of applications.

猪饲料中通常补充有铜和锌，但排泄的> 90％的金属被排泄，最终积累在用液态猪粪（LSM）处理过的土壤中，以满足氮（N）的要求。在2002年至2015年之间，在埃布罗山谷（西班牙东北部）进行了玉米田间试验，以确定长期施用LSM的两种速率[30和50 m ³  ha ^-1，约等于220]（218）和〜390（389）kg N ha ^-1 ]相比较于0和300 kg N ha ^-1矿物肥料。300 kg N ha ^-1处理后，观察到植物中最高的Cu浓度（5.03 mg kg ^-1）。处理不影响植物的锌水平（〜21 mg kg ^-1）。所有全植物和谷物中的金属浓度均低于动物和人类摄入的阈值（30 mg Cu kg ^-1和500–1300 mg Zn kg ^-1）。12年后，在低和高LSM速率下，第一年（2002年）的土壤有机碳（SOC）为13 g kg ^-1分别增加了19％和26％。矿物肥料（300 kg N ha ^-1）的SOC增加了22％，0 kg N ha ^-1的控制处理也使SOC上升了11％。LSM施用12年后似乎对玉米产量没有不利影响。