How much weather and soil type influence nitrate losses

Published 28 February 14

How weather and soil type affect nitrogen losses via leaching and ammonia emission.

Key Messages:

  • Factors influencing nitrogen lost due to leaching include: the amount of rainfall following application and overwinter drainage, soil type and available nitrogen in the slurry
  • Weather conditions at or shortly after spreading will affect ammonia losses
  • Incorporating manures into ground no more than six hours after application will reduce ammonia emissions
  • Using a shallow injector will reduce ammonia emissions by about 70% compared to surface broadcasting.

The effect of weather and soil on nitrogen use efficiency is a new DairyCo video now available on YouTube.

In the video, Dr Lizzie Sagoo, ADAS soil scientist, explains how a number of factors influence the amount of nitrogen lost via leaching when slurry is applied in the autumn and winter period. These include:

  • The amount of readily available nitrogen in the manure that is at risk of loss - slurry has a higher ammonium-N content than FYM so losses will be higher
  • The amount of rainfall and overwinter drainage following application - with wetter areas experiencing more leaching
  • Soil type - with nitrate leaching tending to be higher on lighter sandy soils than on heavy textured soils.

To help farmers take account of these losses and calculate what remaining nitrogen is available to the crop, the latest version of MANNER-NPK uses postcode-specific climate data and soil information to estimate nitrate losses following a manure application event.

“Once you’ve enter your postcode, MANNER NPK will calculate monthly values for rainfall, evapotranspiration and drainage for that location,” explains Dr Sagoo. “The climate model also calculates the average rainfall between manure application and the end of soil drainage. These figures can be edited in an exceptionally wet or dry year.”

“You can then select the top and subsoil texture in the field and, from this, MANNER-NPK calculates the soil hydrology and takes it into account when calculating your nitrate leaching,” she explains.

What role does weather play when calculating ammonia losses?

Research has shown that weather conditions at, and immediately following, slurry application have an effect on ammonia losses.

Ammonia emission following summer application of cattle slurry to dry soils is usually higher than to moist soils, due to a combination of the hydrophobic effect of dry soils on slurry infiltration and higher temperature, lower humidity conditions in the summer. Emissions after application increase with wind speed and reduce after rainfall as the slurry is washed into the soil.  These factors are taken into account by MANNER-NPK when estimating ammonia losses.

Reducing ammonia losses

“Incorporating manure into areas due to be reseeded can be very effective in reducing ammonia emissions,” explains Lizzie. “With most emission occurring within six hours of application, the sooner after spreading the incorporation takes place the more effective it is.”

The best way to minimise ammonia losses on grassland where incorporation is not an option, is by applying slurry using a shallow injector or bandspreading equipment. Typically, applying using a shallow injector will reduce emissions by about 70% compared to surface broadcasting. Using bandspreading application can also reduce emissions by between 30 and 60% compared to surface broadcasting.

Within MANNER NPK, you can enter details of application method and soil incorporation and this will be taken into account when estimating ammonia losses.

For more information about MANNER NPK and to download the program go to http://www.planet4farmers.co.uk/Manner.