Many late drilled crops have been sitting in saturated, compacted and anaerobic soils for some time. In these cases plants' ability to access nutrients will be reduced. Consequently, nutritional requirements are significantly different and Frontier says vigilance on application timing is especially important.
When to apply?
There is a need for early nutrition this year but this should only begin when soil conditions reach around 8oC.
Mike Slater, Fertiliser Technical Development Manager for Frontier explains: "Below that, there is minimal microbial activity and plant growth requires oxygen in the soil as well as moisture. Water levels in soils need to fall to allow oxygen back in, otherwise nitrate will be lost."
Crops mainly use nitrogen as nitrate and conversion of ammonium ions to nitrate (nitrification) also requires soil temperatures to be around 7 to 8oC.
NB: Urea is highly soluble and, if applied to waterlogged soils, could leach before converting into the 'safe' ammonium form.
Nitrate is highly mobile in soil and efficient use will not be achieved until soil conditions are suitable for spreading.
Go early, little and often
Although soil nitrogen levels were higher than usual in autumn 2012, significant losses have been measured during the winter period. This has led to between 20 to 30kg N/ha less than is normally seen at this time of year. Even following oilseed rape crops, soil nitrogen levels have been recorded at index 0. And following cereals, they are in the mid to lower part of the index.
These measurements (taken to 90cm depth) show only part of the problem. This is because early season growth this year is taking place only in the first 20 to 30cm of soil. Usually by now roots are down to around 40 or 50cms depth and therefore have access to a larger area of soil and nutrients than they do this season.
Mike advises: "Consider an early, small application of nitrogen at the onset of spring growth. This will aid early development while limiting the risk of losses from leaching on very wet soils.
"This is a year when mineral nitrogen testing could be very valuable not just to identify fields high in soil nitrogen but also those fields very low in nitrogen where an early boost will be essential.
"Plan to apply a small quantity of nitrogen when conditions allow, 30 - 35kg/ha for cereals and 35 to 45kg/ha on oilseed rape. Although this may increase workload, it will pay dividends if crops achieve good early growth."
With restricted rooting this year all crops will struggle to take up nutrients and this will be compounded on lower index soils. Soil conditions are severely restricting root development leading to nutrients being sought from smaller volumes of soil.
Every effort should be made to try to increase root growth:
1. Ensure crops can access water soluble phosphate
Roots require phosphate in order to grow and they seek this out in soluble form from the soil. This year, restricted rooting means plants will only be able to access a smaller volume of soil - potentially reducing their phosphate uptake. An early application of ammonium phosphate (e.g. DAP or NPK(S) is advisable.
If a foliar spray is required (for speed of effect) then a product containing phosphate is the best choice in low index soils. Nothing will replace phosphate that is applied in fertiliser form but where speed is necessary, foliar treatment at the two-three leaf stage may give some benefit.
2. Stimulate root growth with phosphite
Although chemically similar to phosphate, phosphite is a growth stimulant. Best results are achieved when used as a seed dressing; but when there is adequate green leaf, foliar phosphite will stimulate root growth by helping the plant scavenge for nutrients. This could give your crop a much needed boost this spring.
Phosphite does not replace phosphate and indeed if applied in soils where phosphate levels are very low then the crop will search in vain for phosphate. However, in normal soil indices (2-3) rooting will be stimulated by phosphite, allowing a greater area of roots to look for the phosphate.
3. Consider PGRs to assist with rooting
Another way to help rooting is the use of added value PGRs (trinexapac and prohexadione Ca). Brian Ross, Technical Support Manager with Frontier says: "These should be applied pre GS31, though crops should be free from stress and have 1-2 tillers. Although these are giberellic acid inhibitors used to shorten crops, applied now they stimulate auxins which are the drivers of greater root development."
Using PGRs in this way will also help in the continuing development of tillers, whose primordia are already set down.
What is clear is that, after a poor start crops will require tender loving care in order to maximise their output.