Archive Article: 1997/08/02
Peat soils require careful management – but the
rewards can be high on these fertile fenlands.
We report on the tactics.
TRACE element deficiencies, low soil pHs and threat from weeds, mean specific crop production techniques have to be refined on East Anglias black peat fenland farms.
Peat normally holds twice as much water as clay which sustains crops in most seasons, but roots going down in search of moisture can be blocked by a layer of soil which is extremely acidic.
"This drummy layer is often only two inches thick but its pH is so low it can kill roots," says ADAS soil scientist Selwyn Richardson.
"I have seen a 2.8pH. Typically the layer is12 to 24in deep but as peat is still shrinking it is getting closer to the top. Wheat roots can go down 5ft and beet even deeper, so freedom of movement can be severely restricted."
Currently it is usually too deep to plough out but it can be broken up by sub-soiling, although acidity still has to be neutralised. Dribbling lime down from a sub-soiler is useless as insufficient can be applied.
The only feasible way to balance pH is to plough it down. But because of increasing the current high risk of manganese deficiency only 3-4t/acre should be applied, which is probably not enough to do a good job.
Manganese and copper deficiencies plus insufficient moisture uptake in a dry season are why long strawed wheat varieties do best on peatland farms.
"They seem better able to cope with manganese deficiency and drought than shorter-strawed types as they have more stem reserves," says ADASs Nigel Simpson.
"Taller types also finish better to give grain with better bushel weight, but are more prone to lodging. In a dry season there is no problem but in a wet one when growth regulators are missed, or an inappropriate rate used, there is a high risk of flat wheat."
Apart from weak stems, lodging is also caused when root anchorage in peat is insufficient to hold a plant with a mass of tillers upright. This, and because establishment is good on peat, is why lower seedrates, typically 140kg/ha, are used.
Weed density on peat is high, with severe infestations appearing almost overnight, so early removal is vital.
But small sugar beet plants are more vulnerable to herbicide than older ones. This is why ADAS is using primed seed and starter fertiliser to boost emergence and early growth – so plants are more robust and better able to cope with spraying.
Faster early growth also makes them more competitive to weeds, and with larger canopies wind erosion risk on blowing-prone soil is reduced.
"Advantage seed and starter fertiliser gives huge benefits for emergence and seedling vigour," Rickwoods Pete Saunders says. "The seed treatment gives a better and earlier start, then the fertiliser kicks-in to get the crop away."
A solarimeter under the canopy allows sunlight reaching the ground and lost to the crop to be measured. By recording the amount arriving overhead that is available for conversion into sugar can be assessed.
Beet sown with primed seed and given a kick-start trapped 57% of available sunlight compared with 49% from an untreated crop.