Time for top-dressing?


05 May 1998


Time for top-dressing?

Having held off with the early top dressing, my winter cereals are starting to take on a yellowish tinge that isnt just down to manganese deficiency. What has been happening in the soil in 1998 and at what level should the main top dressing be pitched?

Now is the time to apply your first top dressing to cereals but be careful as the potential to increase lodging, particularly in first wheats, is high this year. Soil nitrogens are well above average levels according to ADAS in a survey sponsored by MAFF.

The nitrogen levels in heavy soils this spring are among the highest on record at 100kg/ha, and on light soils the 74kg/ha of soil mineral N is a record value at some 16kg/ha above the long term average. These high levels are further reinforced by the soil mineral nitrogen levels after oilseed rape which, at a mean of 130kg/ha, are 25kg/ha above the figures for the last two years.

Higher than average over-winter temperatures, and lower than average rainfall, have contributed to these high levels which mean fertiliser rates for first wheats, in particular, have to be worked out with care.

Overall nitrogen management for milling wheats will be important this year as, with one of the highest percentages of crop down to milling varieties, quality will need to be high to secure good premiums.

Guard too against malting barley varieties with higher-than-average grain nitrogens. In high risk cases it might be worth considering going instead for maximum yield.

Farm soil testing will give a precise indication of N reserves but in the absence of testing growers should consider crop colour, vigour and development as indicators of available nitrogen.

How much to apply will also depend on grower expectations of grain price after the next harvest. A grain price near £80/ t suggests a reduction of 10-20kg/ha for optimum returns, compared with a £100/ t end price.

If Sterling devaluation and a more positive market outlook lift prices to £90-95/ t during the next marketing year, this would imply a reduction of just 5-10kg/ha in optimum nitrogen inputs.

Dr Brian Chambers, ADAS Gleadthorpe, Notts.

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