By Andrew Blake
GOOD SAVINGS are on offer to combinable crop farmers in most parts of England and much of Scotland this season. Reserves of available nitrogen in many fields are much higher than usual, says ADAS.
As forecast, the dry winter means cereal and oilseed rape growers should be able to slash overall N inputs by up to 30kg/ha (24 units/acre), says senior research soil scientist Peter Dampney.
“It could have been different if the heavens had opened. But soils in the main arable areas are drying out and temperatures are picking up. So it would take a lot of rain to alter things now.”
Potential savings are confirmed by ADAS sampling at 80 sites as part of Nitrate Vulnerable Zone monitoring, says Mr Dampney.
“A consistent pattern is emerging. By mid-February, between 10 and 30kg/ha less N had been leached than in a normal year.”
The high price of nitrogen is another reason for easing back on total inputs. But breadmaking wheat growers aiming at 13% should be wary, as cuts may be inappropriate, he warns.
The main time for saving is at the start of the season when the relatively small plants can obtain enough N from the soil. “That”s why a lot of people have held off top-dressing, and rightly so.”
Farmers and advisers using the RB209 advisory book should be sure to use the correct tables to assess soil nitrogen supply (SNS) indices. Excess winter rainfall (EWR) is the key.
Use table A (under 150mm EWR) in most areas of England, table B (150-250mm EWR) in the north-east and parts of the West Midlands and south coast, and table C (over 250mm) in the far west, he advises.
Growers set to benefit most are those on medium and heavy soils with crops after cereal breaks, and regular organic manure users, especially those who have applied them since last autumn.
Not all will be able to cut N inputs, warns Mr Dampney. “Where the SNS index is 0 or 1, the effects of a dry winter are minimal. Also, on easily leached sandy or shallow soils, the available N is lost quickly and most will be gone.”
Despite price rises nitrogen remains highly cost-effective, albeit at slightly lower rates. Adjustments to RB209 will depend on where the break-even ratio lies, he explains.
These are based on ratios of 3:1 (ie 3kg of grain needed to pay for each 1kg of N) for winter cereals and 2.5:1 for oilseed rape. This year many growers are working to ratios of 5 or 6, which merit adjustments, he points out (see table).