Growers urged to adjust final N application

Cereal growers are being urged to reassess the potential yield of their crops, as there maybe scope to cut back on the final nitrogen split if this is drastically down on the original yield target.

There was a desperate need for crops to tiller well this spring to compensate for the thin crops, but their failure to do so has resulted in sub-optimal shoot numbers and dilemmas for many growers planning their final nitrogen applications, says Mark Tucker from Yara.

Like many agronomists he predicts that the growth stages will now play catch-up as temperatures rise. He explains that because winter cereals are photoperiod-sensitive, the increasing day length triggers the start of flowering, which has now happened. The setting of grain sites is now under way and needs encouraging in order to regain any yield potential lost because of the low shoot and ear count.

“The aim of the nitrogen game is now to try and extend the process of floret initiation/survival for as long as possible, which will generally stop when there is competition for stem carbohydrate and N availability. Adequate supplies of N encourages faster floret initiation and also will increase the duration of initiation.”

He gives two examples, which are also useful rules of thumb for calculating your potential yields this year:

First, with 20 spikelets, each with two to four florets, this gives 40-80 potential grain sites/ear. So, 346 ears/sq m x 50 grains/ear x 52 mg/grain (average grain weight) is equivalent to 9t/ha. But second, if there are only 200 ears/sq m, the potential is lower at 5.2 t/ha assuming the same grain weight and number/ear.

The N recommendation from now on, therefore, has to be based on a review of this yield estimate, which he suggests needs re-evaluating on a field-by-field basis.

“Do some shoot counts to establish your yield target. If this is drastically down on your original plan then a reduction of 20-25kg N/t of production lost could be worthwhile. This is assuming they were somewhere near the optimum of 230kgN/ha in the first place.”

“Use analytical tools available to determine leaf nutrient status – either foliar analysis, or N-Tester for non-destructive nitrogen tests to be certain.”

He warns that levels of plant N are critical to maximising floret number and survival.

“For the youngest leaves maintaining N-levels of around 4% is still a key factor in maximising the potential of each plant. Generally if a plant has poor above-ground biomass it will have poor below-ground biomass giving low nutrient use efficiency, hence the need for more plant nutrition inputs on these poorer crops.”

Looking ahead, for many it is just the final dressing that may be left to go on. “If the wheat is for milling then the premium will be a vital aspect of your gross margin and should be given full consideration.”

More on this topic

Farmers Weekly Academy: For more information on cereal nutrient management and to collect BASIS and FACTS points, take the online academies for nitrogen management – Fertiliser 4: Micronutrients for arable crops and Fertiliser 2: Remote sensing

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