Cover cropping fallow to restructure soils
Growers who are unable to get spring cash crops sown in good time and in suitable conditions should consider planting a cover crop instead.
That’s the advice from RAGT’s forage and soil health crops manager Helen Wilson, who says the benefits of growing a cover crop to help badly damaged and sodden soils recover in time for next season should far outweigh the cost of growing it.
“A suitable cover will help restructure soils by putting down masses of roots. This will also help by pumping out water through the leaves to aerate the soil. It will also add organic matter and encourage soil biology, including earthworms.
“This all leaves soil in much better condition than leaving it bare, reducing or eliminating the need for remedial cultivations in the summer and giving the following crop a much better start.”
It can be difficult to persuade growers to spend more money, especially if they have bags of seed sitting in the shed they have already paid for, she admits.
“It is very tempting to continue with the programme. However, smearing crops into already-damaged soils is throwing good money after bad. Spring crops have a short growing season so anything that holds the crop back should be avoided, including cold, wet seed-beds and compaction. You also risk damaging your soils further if you cultivate when they are wet.”
Waiting for better conditions might not work either, she adds. “Once we get into mid or late April, depending where you are in the country, I’d suggest spring crops are very unlikely to cover their costs. You might as well save your seed for next year when it will do some good.”
Planting the right cover crop will deliver substantial benefits even if it is only in the ground for a couple of months, although the longer it is left, the more good it will do, she says.
There is no set cut-off date for drilling a cover crop. “All suitable species will romp away once soils are warming up, so in most cases you can wait until soils are capable of carrying machinery without damage.”
May or June are ideal, although crops can be sown into July. “That should still give 10-12 weeks of growth and enough time to destroy the cover crop and prepare the ground for the following crop.”
There three main groups of cover crop suitable for use at this time – deep rooters, fibrous rooters and fertility builders, says Helen. “I suggest keeping things simple – the right combination of two or three species will do a good job.”
Oilseed radish and mustard have strong roots that reach 1.5-2m deep, breaking through compaction and opening up soils, improving drainage and encouraging earthworms to burrow.
“If you grow oilseed rape use our oilseed radish, Terranova, which is resistant to clubroot,” says Helen.
Rye and black oats have more fibrous root systems that condition and draw moisture out of the mid and upper soil layers.
Phacelia is shallow rooted so provides the same benefits as above in the seeding zone. The roots will also follow radish and mustard roots down.
“The cheapest option would be a white mustard/rye mix, but avoid if growing oilseed rape. Rye also takes longer to grow then black oats, so might not be the best choice if time is limited.
“Black oats cost more but are very popular as they produce biomass really quickly and have more vigorous root systems. These, along with oilseed radish and phacelia, would be my mix of choice. You could use vetch as the third choice if you want to fix N ahead of the next crop, or berseem clover, which is a better rooter.”
Cover crop management
Cover crops should be drilled in to a shallow seed-bed, says Helen. “As long as there is moisture present you don’t need to do too much; a light covering is sufficient.
“Seeds of different sizes can separate in the drill, so don’t put too much in at once. I’d recommend 40kg/ha of N to kickstart establishment as residual N levels are likely to be low.
“If there is a serious weed burden at drilling it might be worth spraying off, but these crops are pretty vigorous so should be able to cope in most circumstances.”
Radish, mustard and phacelia will flower about six weeks after sowing. Topping will prevent seed set and help maintain active root growth, although it is not essential, says Helen. “Species such as oil radish and mustard will bounce back, but Phacelia might be checked.”
RAGT cover crops can be mixed to suit individual requirement, budgets and the time of year, says Helen. “They are available from local merchants across the country, so growers can have a chat with them or contact me contact me directly for advice (email@example.com).”
Cover cropping fallow – key points
· Restructures soil
· Pumps out water
· Boosts soil biology
· Increases organic matter
· Reduces or eliminates need for remedial cultivation
· Flexible sowing dates
· Easy to establish
· Improves following crop prospects