A global meta-analysis of fertiliser management on soil available and total zinc

Soil available and total zinc are important indicators of soil zinc status, yet the global effects of different fertilisation practices on soil available and total zinc and the drivers of their variation remain insufficiently quantified. We conducted a global meta-analysis based on data extracted from published field studies. A total of 1 240 paired observations of soil available zinc from 94 studies and 364 paired observations of soil total zinc from 44 studies published between 1993 and 2024 were compiled. The effects of eight fertiliser types (mineral fertilisers without zinc [CF], compost, manure, zinc fertiliser, CF combined with either compost [CFC] or manure [CFM] or zinc fertiliser [CFZn], and compost combined with zinc fertiliser [CZn]) on the soil available and total zinc content were assessed by meta-analysis. The results indicated that compared to the control group, soil available zinc content increased significantly under treatments CZn, CFZn, zinc fertiliser, CFM, manure, CFC, and compost by 158, 134, 133, 84, 78, 43, and 35%, respectively. Additionally, manure, CFM, zinc fertiliser, CFZn, and CZn treatments significantly enhanced soil total zinc content, with increases ranging from 25% to 32%. Applying zinc fertiliser at > 20 kg Zn/ha significantly increased soil-available zinc. In the medium-rate CZn class (10-20 kg Zn/ha), soil available zinc increased from 0.78 mg/kg in the control soils to 3.46 mg/kg in the treated soils. Among crop systems, wheat showed a stronger response in soil-available zinc, whereas rice-growing systems showed relatively larger increases in soil-total zinc under manure and CFM treatments. Fertilisation intensity, crop types, soil organic carbon, and soil pH emerged as key drivers of variation in soil available zinc, whereas the main drivers of soil total zinc varied among fertiliser types and were more often associated with fertiliser rate and crop types. When soil organic carbon was ≤ 12 g/kg or soil pH was > 7.5, applying CZn at 10-20 kg Zn/ha showed greater potential to increase soil available zinc. These findings suggest that soil zinc management should be optimised based on fertilisation intensity, crop type, soil organic carbon, and soil pH to improve zinc availability while avoiding excessive accumulation.