How maize silage analysis can reduce fertiliser spend

German growers are using maize silage crude protein levels to gauge the next year’s fertiliser requirements, resulting in reduced leaching and input costs.  

Crude protein levels of 8-8.5% in harvested maize samples can signify a need to cut nitrogen input by up to 60kg/ha overall, potentially saving more than £300/ha.

This is according to German Maize Committee president Friedhelm Taube, Kiel University, who said money could be saved without yield losses.

See also: Maize Watch: Advice on reducing soil erosion post harvest

Research shows maize fields producing silage analysing at 7.2% crude protein or more leach more nitrates.

Nitrogen (N) surpluses average close to 100kg N/ha on UK farms.

“On livestock farms with 1.2 livestock units a hectare, it is feasible to reduce the surplus to 60kg,” Prof Taube told Farmers Weekly. “German research shows that roughly 75% of the surplus is directly linked to negative environmental effects and 37kg is lost through leaching.”

He says more than 70% of German farmers are oversupplying N because they are forgetting about the N in the slurry.

Simon Draper, independent agronomist for the MGA, agrees, suggesting that, in many cases, UK farms could cut nitrogen by 40-50%.

How it works

The process uses a standard maize silage analysis used at any commercial or academic laboratory.

The growers then consult a table (see “How maize crude protein affects nitrogen advice”) based on a growing body of research evaluating how N concentration in maize is affected by:

  • Leaching 
  • Rain
  • Crop maturity and dry matter

UK maize production has historically seen crops take 100-110kg N/ha to grow, with nitrate vulnerable zones limited to applying 150kg N/ha – the N-max limit.

Further research is needed to understand how N is stored, released and used in the soil profile form year to year as a “nitrogen bank”, said Prof Taube.

How maize crude protein affects nitrogen advice

Crude protein level (%)

Action on nitrogen application

6.5-7

Optimal – no change

7-7.5

Reduce nitrogen input by 20kg/ha

7.5-8

Reduce nitrogen input by 40kgha

8-8.5

Reduce nitrogen input by 60kg/ha

Nitrogen profiling

The German work is a simplified version of a N predictor service currently available in the UK.

The MGA provides N fertiliser guidelines based on a maize silage sample and individual farm information on a myriad of factors (see “Factors affecting nitrogen inputs in maize crops”).

The service is free for MGA members, but is available to non-members for £20 .

Factors affecting nitrogen inputs in maize crops

Why a crop may need less N

Why a crop may need more N

  • Early-maturing varieties
  • Early harvesting
  • Heavy soils
  • Soils that have been subsoiled in the past year
  • A previous legume breakcrop
  • A previous grass ley (length of ley decreases need for extra nitrogen)
  • Rotation includes livestock, grass or organic manure
  • Drilling mid-May or later
  • Low rainfall in autumn and spring
  • Slurry application – after February can mean more of a saving
  • Late-maturing varieties
  • Early harvesting
  • Light soils
  • Not subsoiled in the past three years
  • Previously in a cereal crop
  • Previously in a maize crop – but to a lesser extent than cereal
  • In an arable rotation with no organic manure
  • Early-April drilling
  • High rainfall in autumn and spring

Friedhelm Taube was addressing the Maize Growers Association (MGA) conference near Derby on Thursday (6 February)

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