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Slurry Evaluation for Second Cut Silage

This year, first cut silage has been harvested early especially on ungrazed fields which are giving very good yields.

Good weather and very little rainfall have allowed an adequate wilting time of more than 24 hours for grass after mowing. This will inevitably mean that first cut silage should be of a high quality for next winter, giving the added advantage of reduced feed costs.

Keep in mind your first silage cut will have removed a lot of P & K and it is best practice to recycle slurry back onto silage ground, and the ratio of P to K (1: 6) in cattle slurry is ideal for this purpose. Exercise care in calculating the value of nutrients in the slurry. Do not overestimate the nutrient value as this can vary depending on a number of factors including amount of concentrates fed to animals in housing and dry matter (DM) content of the slurry being applied.

To determine slurry DM content, farmers should invest in a slurry hydrometer to measure the samples viscosity, this can then be used as an indicator of nutrient content. To get a more complete picture, do a chemical analysis of your slurry. In all cases, make sure the sample taken is representative of the tank overall and therefore, you should take this sample after agitation.

Typically, thick cattle slurry has a DM content of 7%, but this can vary as the contractor or farmer may have added water to ease the spreading operation, consequentially decreasing DM and diluting the nutrient value content.

Nitrogen value from slurry can increase by up to 3 units by changing from splash plate application to injection or trailing shoe method of application.

Nutrient value of slurry

1000 gallons of Cattle Slurry at 7% DM

 

N

 

3-5 units

P

 

5 units

K

 

30 units

1000 gallons/ac of Pig Slurry at 4 % DM

 

17-19 units 7 units 20 units

 

It is important to note that:

  • P availability from slurry is reduced by 50% on soils that are Index 1 & 2 for P
  • It is recommended on soils that are Index 1 & 2 for P to only use 50% of the crop’s requirement in the form of organic P and use the remaining 50% as an available water-soluble P form, such as that from chemical fertiliser
  • K availability is reduced to 90% on soils that are index 1 & 2 for K
  • It is best practice to spread slurry on a dull damp day to get better nutrient utilisation and to minimise its impact on the environment.

To learn more about compiling a slurry and fertiliser programme for second cut silage, contact us here

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