The large variation in Nitrogen (N) requirements between and within was noted today by Daniel Kindred, Senior Research Scientist at UK based ADAS Boxworth.

Speaking today at the National Tillage Conference in Kilkenny he said: “Accounting for the N requirements seen between fields is challenging.”

He said that current fertiliser recommendations can only ever be right on average and conceal a lot of variation that exists between fields.

He added: Accounting for this variation is challenging because normally many factors are confounding, for example testing has been under taken on different fields on different farms with different managements and different varieties in different years.

Kindred noted it is hugely important for farmers to understand N requirements and its variation. He outlined three components key to its understanding; crop demand, soil supply and fertiliser recovery. He said: “We know how much the crop needs to grow a certain tonnage, we can estimate how much comes from soil supply, however we don’t yet have an understanding of N recovery from fertiliser.”

He outlined the findings of recent research within fields which has also shown a large variation in N requirements. Both between and within fields. He noted that the main causes are in the soil and are not yet understood. He stressed that the use of precision farming technologies and variable rate applications have the scope to deal with this variation with fields.

However he noted: “With the variation within and between fields so large, precision in N management cannot be high, what matters is that N rates are correct on average across the farm management block.” He said this requires the ability to test and measure the variation.

He told attendees to accept that errors in the prediction of N requirements are common and larger than you would like. However he stressed that predicting gross variation is most important particularly over large areas.

He advised farmers to characterise ‘typical’ fields on the farm, accumulating evidence and data from multiple sources to judge N sufficiency and to consider testing N responses. Identify situations where N use may be very different. He said: “Be bold in making adjustments so you learn how to use N better.”