Farmers harvesting maize are being warned to limit surface run-off and soil loss that could pollute watercourses and cause flooding.

Wet weather had softened ground, increasing the risk of soil running off fields into waterways, said the Environment Agency.

Research had shown a substantial increase in run-off from soils compacted by heavy machinery. As well as causing flooding, run-off from maize fields could carry chemicals and soil into rivers and streams. This could smother the spawning grounds of trout and salmon and harm other aquatic life, the agency said.

Growers should prevent soil loss by roughening and loosening the soil surface immediately after harvest, said agronomist Simon Draper, working on behalf of the Maize Growers’ Association.

Harvested fields with soil damage should be ploughed or chisel-ploughed in strips to cut soil compaction. Headlands and wheel ruts should be a priority as they acted as pathways for run-off, he added.

But deep soil compaction should not be tackled until soils were drier at depth, which would probably be next year.

Planting early-ripening maize varieties would allow farmers to get onto fields earlier before soils became wet and still achieve high yields, said Mr Draper. This would also give them more time to tackle post-harvest soil problems.