A warm autumn and a mild winter haspresented farmers with large, forward crops this spring with some carefuldecisions to make, says Ian Matts, company agronomist at Yara UK.
In well-established leafy crops such as OSR,which contain large amounts of nitrogen in the canopy, it is likely to meanmuch lower optimum rates will be needed to reach the required canopy size priorto flowering , suggests Mr Matts: However, it is still important to determineoptimum N rates. This can be done by monitoring the crops using tools such asthe ImageIT app which measures N uptake in OSR crops and generates an Nrecommendation based on digital photographs.
Mr Matts also advises that growers shouldnot be tempted to delay the timing of first applications because crops aregrowing well, especially on light soils: Warm weather has meant spring growthhas occurred early this year and you cant stop a crop from growing ifconditions are right. But if not fed albeit with a smaller dose – low levelsof soil N may encourage such crops to bolt.
Foliar N applied at flowering is also worthconsidering for OSR crops requiring low levels of spring N and, keeping thecanopy greener for longer, will boost yields. In over 7 years of trials work this application has produced an averageyield response of 0.35 t/ha, advises Mr Matts, so it is well worth theinvestment, with early to mid flowering identified as the optimum timing. Such foliar applications can be combined witha sclerotinia spray, reducing the time and costs involved in a separate passthrough the crop.
In some areas, a second excessively wetwinter has led to saturated soil with low nutrient levels. According to ADAS data Excess WinterRainfall (EWR ) the amount of rainfall that drains through soil has beenabove average in central and southern England, although close to the long termaverage elsewhere. This is likely tolead to the more mobile nutrients such as nitrogen, sulphur, and boron being leachedfrom the soil away from the rooting zone.
Water logged soils may also have led tocompaction in the soil profile, advises Mr Matts, this will cause problemswith rooting reducing plants efficiency in uptake of both soil N and appliedN. Growers must also take care not to overlook other crop specific nutrients,such as boron for oilseed crops.
In wheat, many late autumn drilled crops arefollowing a similar pattern to the previous years crop: backward and stuntedwith a small root mass.
As in 2013, early N will play an importantrole for such crops, says Mr Matts, to encourage tillering. However, as Yara trials have proven, too muchearly N at the expense of the later timing can in fact be detrimental to yield,creating a large energy hungry canopy which can run out of steam. With these crops it is important to rememberthat not only should the first dressing be increased, but so too should thetotal dose, with last years optimum on average 20kgN/ha above the long-termYara average of 230kgN/ha.
Know your crops development
With weather being so variable, even unseasonable, across the country and insome areas affecting soil structure and root biomass, the key consideration isto monitor crops.
Assessing crops, field by field, usingtools such as the Yara N sensor, N Tester and the ImageIT app, rather thansticking to a rate chosen early in the season is vital, suggest Mr Matts.
The N sensor determines a crops Nitrogendemand by measuring the crops light reflectance as the tractor passes. It thenuses this data to vary the rate applied from the optimum chosen for the fieldsending a signal to the spreader or sprayer which will variably adjust thelevels of application across the field. Absolute N calibration for the N sensor, available for oilseed rape,builds on this to make a recommendation at the time of nitrogen application.