Early spring N is unjustified
Early spring N is unjustified
ADVICE from a DEFRA-funded study of soil mineral nitrogen reserves and winter rainfall echoes industry calls to delay early N.
Crops are well established, well developed and looking very green and healthy, so in many cases there is no need for the usual early bag of nitrogen in mid to late February, says ADAS soil scientist Peter Dampney.
Average winter rainfall, with most of arable England receiving less than 150mm of excess rain (rainfall that drains through soils) up to the end of January, has helped preserve residual soil N left last harvest for use this spring.
Soil testing also revels a normal pattern of soil mineral nitrogen reserves. As such shoot populations at the start of stem extension (GS31) should now dictate N use in cereals.
For winter wheat the target is about 1000-1200/sq m, equivalent to 3-4 shoots/plant. If the shoot population is around 800/sq m or more in mid-February, the crop is progressing well and no February N is needed, advises Mr Dampney.
But some early drilled crops will stop tillering quite early. If GS30 is reached in early or mid March, and shoot number is borderline, it may be worth considering 40-60kg/ha N to help maintain shoot numbers, he says.
However, the first main N dressing should not be considered before late March.
For thin or backward rape, less than 15cm tall one-third of the total N dressing from mid-February could be justified.
For further advice and updated winter rainfall maps see www.adas.co.uk/springN. Main spring N advice will be given in late March. *
Charles Abel
Excess winter rainfall in mm