Boost maize yield by treating suffering soils

Maize growers could produce an extra 7.4t/ha (3t/acre) through better soil management, farmers attending a recent DairyCo discssion group were told.

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With maize worth £30/t, that could boost incomes by £222/ha (£90/acre). However, many soils are now too wet to travel on, so what can farmers really do to improve them?

Richard Smith, principal land quality officer at the Environment Agency, reckons extreme circumstances warrant urgent action. Speaking at the discussion group near Frome, Somerset, Mr Smith said farmers should subsoil compacted fields now to reduce runoff and erosion, even if it meant further remedial work in the spring.

“The water table isn’t as high as people think – it is a common mistake that farmers are making at the moment, They see water lying on top of the soil and think it’s saturated.” However, two appalling years meant many fields were badly compacted, preventing water from infiltrating soil, and damaging crop growth, he added. Many soils were actually dry underneath compacted layers.

The first step to improving soil quality, and therefore yields, was to dig a few test holes across fields to ascertain whether compaction was an issue, said Mr Smith. “When soil is compacted, the crop’s just growing in the top of the soil, which isn’t maximising its potential.”

Farmers should also look out for anaerobic, dark-coloured layers which may have been caused by ploughing slurry into wet conditions and would also prevent root growth.

Once producers found the depth of any compaction, they could then either plough or subsoil to remove it – but badly compacted or anaerobic soils may require annual subsoiling to produce significant improvements.

Neil Darwent, who hosted the event at Walk Farm, Withiam Friary, reckoned he could boost maize yields from about 35t/ha (14t/acre) to 42t/ha (17t/acre) if he could improve soil sufficiently. Following two wet years, his clay soil was badly compacted in places, and suffered some surface runoff following heavy rains.

The key problem for many farms on heavy land was the lack of government support for land drains over the past 20 years, said Mr Smith. “I think the main reason we’ve got so many flooding problems at the moment is because we’ve got no land drainage – you can’t blame farmers for that.”

Stone-filled land drains, which last about 20 years, would cost about £4800/ha (£1943/acre) to install, said Piers Badnell, south-west extension officer for DairyCo. Farmers would, therefore, not recuperate the expenditure for another 22 years, although they could benefit from an uplift in land value, he added.

“Soil-filled drains would be cheaper, at around £2880/ha (£1134/acre), resulting in a payback period of about 13 years. However, it is not clear whether fields would produce a full yield response for all that time.”

Another alternative could be mole ploughing, at a cost of just £74/ha (£30/acre). “Even if this only improves yields by half the anticipated 7.4t/ha (3t/acre) this would pay for itself in the first year alone.”

Other options included novel cropping and subsoiling. Mr Darwent planned to plough then subsoil his fields to improve the drainage and soil structure, and then plant turnips, spring oats, forage rape or red clover, according to the field rotation. These would help to dry out soil, while tap roots would pierce the compacted layers, improving soil structure.

“It is a vicious circle,” said Mr Smith. “Once you get compaction it’s a spiral and it gets worse and worse.” However, the same was true of the upward spiral on good soil, whereby deep roots produced heavy crops and more sustainable field use.