Cattle and sheep can be considered four-legged fertiliser factories.

Their manure is not as concentrated as bagged fertilisers (or poultry litter).

However, when overall stocking rates are high or when livestock spend a lot of time in a restricted area, such as a sheep camp, they deposit nutrients in significant amounts.

The dung of ruminants has moderate levels of phosphorus (P) and nitrogen (N).

Typical concentrations are 0.8 per cent P, or eight kilograms per tonne and 2.2pc N, or 22 kg/tonne.

The urine has appreciable levels of nitrogen and potassium (K).

A dry sheep excretes around 145 kg dung per year, measured as dry matter.

At a stocking rate of 10 dry sheep equivalents per hectare, the output is 44 kg N, 10 kg P and 19 kg K - all per hectare per year.

This contribution of phosphorus is equivalent to 113 kg/ha single superphosphate annually.

However, this fact does not mean that manure adequately replaces fertiliser on an average farm.

Manure is spread unevenly and there will be losses of nutrients due to the volatilisation of N, soil fixation of P and the removal of animals for sale.

In stock camps, around water points, under shade trees and in other areas where animals congregate, there are often high levels of soil nutrients.

Generally, these areas do not need additional fertiliser and may be skipped when spreading products.

Where overall stocking rates are high, say three fully-grown cattle per hectare and above, it is likely that only nitrogen needs to be added to ensure maximum plant growth.

Phosphorus, potassium and lesser nutrients should be adequate.

Intensive dairies and some paddocks of feedlots are in this situation.

The effluent from intensive livestock operations will be a substantial resource.

Effluent disposal paddocks should be moved periodically, eg. every five years, to take advantage of the nutrients over a larger area.

The more feed brought onto a farm, the more nutrients end up in paddocks via grazing animals or effluent disposal systems.

Only soil testing will reveal how much nutrient is in a paddock and whether fertilisers can be eliminated completely.

One useful reference text is Fertilisers for Pastures, available from the NSW Department of Primary Industries at www.dpi.nsw.gov.au/agriculture/resources/soils/improvement/pastures

Contact Ashley Senn, Richmond, (02) 4588 2100, ashley.senn@dpi.nsw.gov.au