Growers reminded to replenish nutrients after straw harvest
© Tim Scrivener Tighter supplies, rising demand and expanding biomass markets mean straw prices are running close to the price of grain in some regions. Many farmers opted to bale straw this harvest for an additional cash injection.
According to the British Hay and Straw Association, merchants are paying in the region of £80/t ex-farm for wheat straw, with barley straw as high as £113/t in the South West.
“At a typical straw yield of 4t/ha, this can deliver £320/ha of additional revenue,” explains Origin Soil Nutrition agronomist Toby Ward.
Considering baling costs, this provides an overall income of £220-£270/ha, so it has proven to be a positive economic exercise this year, he says.
However, growers should not forget to replenish nutrients removed by the straw- particularly potassium (K) and phosphorus (P).
“At about £30/ha to replace both the P and K removed from baling straw, it’s a false economy to take shortcuts, as both nutrients are yield-limiting,” he adds.
There is still a £190-£240/ha gain from selling the straw, even considering nutrient replenishment costs.
See also: Post-heatwave nutrition advice for autumn crop success
Online calculator available
A free online calculator from the Potash Development Association (PDA) can help growers keep on top of P and K requirements.
According to the calculator, a 10t/ha wheat crop without straw baled, requires 65kg P2O5/ha and 55kg K2O/ha to maintain soils at the recommended soil indices of 2 for P and 2 for K.
However, PDA co-ordinator Ian Matts says many soils are below these critical levels and replenishment levels increase significantly when straw is removed.
“In this case, off-take increases to 70kg P2O5/ha, but potash removal increases to 105kg K2O/ha each harvest.
“Although there is a small rise in phosphate requirement after baling, potash removal is almost double.”
Replenishment options
Growers have several options, including manures and digestates, although such materials should be analysed for nutrient content, advises Richard Ward, technical sales manager at ICL Growing Solutions.
Some growers opt for individual straights such as triple superphosphate or muriate of potash, but there are benefits to applying P and K together, he says.
“Polysulphate-based P and K fertilisers are particularly popular for both autumn and spring use.”
“Combining polysulphate [48% SO3, 14% K2O, 17% CaO and 6% MgO] with additional P and K makes good sense in autumn or spring starter products.
“For crops with straw incorporated into the soil, a balanced PKpluS like a 0.20.20 containing the P and K alongside sulphur, magnesium and calcium is ideal.
“When growers remove straw, a PKpluS 0.15.30 is likely to be more suitable due to the higher potash offtake involved.”
