Managing nitrogen with a realistic eye on yield potential

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With Nitrogen prices at an all-time high, it is more important than ever that growers realistically evaluate the true yield potential of their crops.

Chris Hoskins, Hutchinsons digital farming manager for the South, shares his views on how best to approach spring fertiliser applications to ensure a viable return on investment.

We have seen such massive variations in purchase price for fertiliser over the last three months, depending on when it was bought, with a tonne of N ranging anywhere between £280 – £700/t – a difference of £242/ha between early and late purchasing.

Indeed, some fertiliser is now costing as much as £2/kg N, so to apply 200kgN could cost anywhere between £162-£404/ha! At these levels it is more important than ever to look at how to reduce or manage applications in the spring as efficiently as possible.

The starting point in this process is to be realistic about the yield potential of crops as this will help to decide where fertiliser will have the most impact and return on investment. Yield maps provide a real and historical picture of the best and worst performing parts of a field – even one year’s worth of data can help to visualise this. 

Within Omnia, it is possible to use several layers worth of yield data to build a yield performance Map , providing a clear picture of what areas of the field perform consistently, or not. In this way, management decisions can be made based on this sub-field information; it may be that a higher yielding area of the field has shown up to be potentially inconsistent, so it may not be worth pushing this area, whereas if another area delivers an average yield and is potentially consistent, it could be worth investing in this.

At the end of the day, the crop needs to be making money or there is not point in growing it so this season more than ever, it is important to take into account the cost of N, the selling price of the crop, as well as yield potential. 

There is a new tool within Omnia, the break-even ratio ( BER ) tool, that does this for you! Based on the cost/tonne of nitrogen and the average wheat selling price, it gives a nitrogen breakeven ratio, allowing for suggested N rates for each crop to be calculated which can then be adjusted, suiting both flat and variable rate applications. 

But how do we know how much to increase or decrease N? There needs to be a realistic appraisal of the yield potential to feed the crop where it will yield. 

If using a variable rate approach, a break even ratio will provide a reference point throughout the spring to refer back to in order to see if certain parts of the field are economically viable to grow. By constantly evaluating biomass through the season, either through tractor mounted sensors or NDVI satellite imagery, it can help to identify and answer the questions should I apply more to poor areas to even up the field or less to these areas as the potential is low.

Trials show that after GS30 in cereals, tiller number and yield potential are set so is applying more to poor areas only worthwhile very early season is a question that must be asked – this year it might be easier to justify. When it comes to the final N application, revisit the same questions again looking at in-season crop data. 

Even at this stage, ask yourself the question, is there the potential for 10t/ha crop or are the break even ratio’s economically justifiable or would it be more realistic to aim for 8t/ha.

Historically it has been the practice to apply more N to poor areas in an aim to even up crops, but this year in light of the high fertiliser prices. a more accurate ‘feed to potential’ may become more common practice.

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