The National Farmers' Union doesn't appear to grasp the seriousness ofsoil structural damage (compaction or squeezing the life out of soil) and its implications for water movement in the environment. My peer-reviewed paper published in December 2013 by Soil Use and Management was referred to by George Monbiot (How we ended up paying farmers to flood our homes, 18 February) and subsequently by Andrew Clark from the NFU (Letters, 19 February). In my extensive field study of 3,243 sites, 75% of land under maize showed serious structural degradation (smeared, rutted and severely compacted) and was producing enhanced surface runoff across the fields. This is inevitable when crops are harvested late in the year (October and November) by heavy machinery.
Some 30% (93 sites) of this degraded maize land carried well-drained, naturally permeable soils over aquifer rocks. Historically, rainfall on these soils readily percolates vertically down through the soil and recharges groundwater resources. After maize cultivation, the damage to soil structure is so severe that rainfall cannot penetrate the damaged upper soil layers, and lateral surface runoff results.
A typical winter atmospheric depression (now referred to in the media as a storm) will produce 20-30mm of rain over a 12-hour period. Optimistically, assuming that up to one half of this rain percolates into these damaged maize soils, this leaves the volume of half an Olympic-sized swimming pool (in excess of 1m litres of muddy water) to be shed laterally across the surface of this "sealed" land for every 10-hectare block of maize stubble. So this winter, when the Meteorological Office reports 30 "storms", every 10-hectare block of damaged land under maize stubble has produced the equivalent of 15 Olympic pools (more than 375m litres) as enhanced runoff. And 196,000 hectares of maize were grown in 2013, an increase of 24% on 2012. How can the NFU fail to understand the implications of this land use for catchment flooding?