Soil nitrogen testing is set to be more critical this spring, as a mixed harvest may have led to large variations of residual nitrogen left in soils.

Last year’s wheat yields were generally better than expected, however, oilseed rape was more mixed increasing the variation in soil fertility this year.

See also: Learn more about managing your soils

Dick Neale, technical manager at distribution group Hutchinsons, says growers will need to weigh up last season’s yield results and consider how much nitrogen has been extracted and returned to the soil through chopped straw, additional organic matter or fertiliser.

He points out that growers who achieved high yielding first-wheat crops will be left with soil that is likely to be depleted of nitrogen.

In contrast, a lot of oilseed rape did not yield as well as expected in 2014, so has not extracted as much nitrogen as normal, and should leave a decent amount behind for any first wheat.

“It is an ideal year for N-min testing, particularly after crops that have potential to return or extract a high level of nitrogen,” he says.

Mr Neale highlights N-min tests cost less than a tonne of fertiliser and will easily pay for themselves by allowing growers to react at the optimum time with the most appropriate inputs.

“It is an ideal year for N-min testing, particularly after crops that have potential to return or extract a high level of nitrogen.” Dick Neale, Hutchinsons

He adds that soil testing will give growers an extra management tool, in addition to Defra’s fertiliser manual RB209, and will help growers understand where it is in the soil profile.

Meanwhile, he warns oilseed rape crops that established well last autumn with a green area index of 1.5 to 2 may have extracted a lot of the residual nitrogen in the upper soil profile, meaning there are not enough nutrients available at lower depths to sustain adequate growth in the spring.

Likewise, RB209 figures may suggest there is 60kg/ha of nitrogen in the soil after the following crop, but that could be mostly in the lower 60cm profile, out of reach of most roots that are still only in the 20-30cm zone.

He also advises growers not to assume that forward crops can be starved of nitrogen later on and stresses a N-min test will help formulate a fertiliser plan based on how much nitrogen there is and where it is in the soil profile.

In addition, more accurate fertiliser strategies could also help manage weed burdens in the spring according to Mr Neale.

He points out that weeds such as cleavers and wild oats are stimulated by high levels of available nitrogen, so more tailored fertiliser applications could help reduce such problems.