I can calculate quantities amounting from rainfall on outside concrete and roofs but cannot discover how to estimate what the animals themselves produce. I have a reasonable idea of water consumption but clearly not all that water ends up in the lagoon.
To
assist producers calculate their NVZ spreading and storage requirements BPEX
have prepared two spreadsheets, one is for those who run continuous flow systems
and one for batch systems as the calculations are slightly different. These can
be found at: www.bpex.org.uk/PracticalAdvice/environmentHub/NVZs.
The spreadsheets use Defra standard data taken from NVZ Leaflet 3: www.defra.gov.uk/environment/quality/water/waterquality/diffuse/nitrate/help-for-farmers
The
Regulations require you to have sufficient storage for 6 months continuous
slurry production; this will include wash water and dirty surface water where
they cannot be separated. If dirty water can be kept separate, then it may be
possible to have less storage (4 months minimum) than for slurry as the closed
periods for spreading will not apply. Dirty water is covered in a Defra Q&A
Factsheet 1: www.environment-agency.gov.uk/static/documents/Business/NVZ_QA_Jan_2010_FINAL.pdf
Whilst
6 months slurry storage may be the legal minimum requirement, an individual
farms needs may be in excess of this because "closed periods" may overlap with
traditional spreading windows. Manure and slurry nitrogen efficiency (NVZ
Leaflet 3, Table 8) cropping patterns, soil types, method of spreading etc., all
have an influence on the amount of storage needed.