'Careless farming adding to floods'
The UK government is discussing new rules to stop farmers contributing to flooding through poor land management.
Experts say careless farming has made floods worse in Somerset and elsewhere.
Some upland farmers have caused soil and water to flush into rivers by leaving fields bare and compacting land with cattle and heavy machinery.
Environmentalists say grants should be withheld if farms are managed in a way that encourages floods - but farmers don't want more regulations.
Scientists are particularly concerned about maize, the crop that creates most rainfall run-off.
Some experts want maize to be banned from steep slopes altogether because its bare rows contribute so much to flooding and silt.
The rules are being discussed in informal consultations, run by the environment department Defra, over what farmers should do to qualify for the £3.6bn grants they receive from the taxpayer.
There is pressure for landowners to capture more rain where it falls in upper catchments of rivers by causing localised mini-floods so the water can seep into the soil instead of flushing into the river system.
In a related project on Exmoor, South West Water is working with landowners to restore the peat bog to improve its water storage.
In the past, farmers have been paid by the taxpayer to dig drainage channels in peat to improve its productivity for sheep and cattle.
Productivity did not increase, but flooding did as water flushed off the moorlands to swell rivers.Blocking drainage
Now we are paying again to reverse the failed policy and fill in the drainage channels.
The scheme costs £2.2m. "It's having huge impact," said Dylan Bright of South West Water.
"By the time the restoration of the catchment is completed, the moor will be able to hold the equivalent of more than 6,000 Olympic-sized swimming pools of water. It'll hold back rainfall from flowing down to places like Exeter."
The sphagnum moss that forms peat holds up to 20 times its dry weight in water.
Preliminary trials on Exmoor by Professor Richard Brazier, from Exeter University, show that blocking drainage channels has allowed the moorland to hold a third more rainfall - this can make the difference between flooding and not flooding.
Prof Brazier is also concerned about land management on farm fields. He said too many farmers leave vulnerable soils bare and allow soil and water to run off.
He claims that current government rules on soil management are often ignored by farmers, who face a 1% chance of an inspection to check that they are earning their grants by obeying the regulations.
Maize farming in the wet west of England is a particular problem, he says, as there are no rules for producing the crop. Three quarters of the maize fields in the south-west contribute to flooding, a report in the journal Soil Use and Management says.
Farm vehicles tend to compact the soil of maize fields, causing massive run-off. "Personally I think the best thing would be simply to ban the cultivation of maize on steep fields," Prof Brazier told BBC News.
Farmers reject a ban on maize on slopes: "We don't need any more regulations on farmers," Mark Humphry told me on his part-flooded farm near Taunton.
"We are working with local Defra officials to get advice on vulnerable soils; that's the best way of doing things."
The National Farmers Union (NFU) is trying to reduce the number of rules on farmers.
Mr Humphry agreed that farmers should do more to protect soils from run-off but said housing, roads and airports were also responsible for making floods worse in Somerset.
But experts say more needs to be done to protect vulnerable soils, like those around the River Parrett which flooded the Somerset Levels.
Professor Bob Evans from Anglia Ruskin University in Cambridge told BBC News: "The National Soil Map makes it clear that some soils on the Parrett catchment are vulnerable to run-off.
"Erosion probably increased in the 1970s-80s because of the change in cropping to winter cereals around that time."
He too is especially worried about maize: "The possibility of erosion occurring in winter cereals is one field in 42, in maize it's one field in seven."
At Cranfield University, Professor Jane Rickson measures the impact of rainfall on different crops and soil types.
"We have to be much smarter about the way we manage the land," she said.
"If we manage soil properly it can absorb a lot of rainfall. We can't prevent flooding but we can certainly inhibit flooding by good land management."Dredging concerns
She said the government's desire to make farming more profitable by encouraging high-value crops like maize, potatoes and asparagus has tempted farmers to plough up grassland that previously used to bind fragile soils together.
Capturing water where it falls was one of the key objectives laid down in the Pitt Review of the 2007 floods and Defra is hoping to expand that work as part of its response to this year's flooding.
Scientists fear that the government will be diverted from the task by the political clamour to increase dredging.
"Dredging will only solve part of the problem," said Prof Rickson.
"If you get dredging wrong, you can make matters worse by making it flood somewhere else. And dredging is an endless expensive commitment year on year.
"It would be better to keep as much soil out of the rivers in the first place."
A Defra spokesperson said: "We are currently seeking views on the rules that farmers need to follow, including soil management and erosion prevention, in return for the CAP funding that they receive."
Follow Roger on Twitter @rharrabin