Nutrient Value of Dairy Effluent

David Armstrong

AK Consultants

Main nutrientsMain nutrients are:

Nitrogen Phosphorus Potassium

Organic Matter

Quantity of nutrients

Detailed research in USA - very useful figures on nutrient output of dairy cows, related to

Concentrations in the feed

Amount of feed consumed

Proportion of dung and manure collected in yards

How the effluent is treated or stored

Dry matter excreted

Total manure dry matter production (in dung and urine);

Approximately 35-40% of dry matter intake.

Cow producing 20 litres of milk:

Feed intake around 19 kg/DM:

Produces 7.5 kg DM as manure.

Nitrogen excreted

Cow producing 20 litres milk/day

Excretes about 400 grams N/day

Phosphorus excreted

Cow producing 20 litres milk/day

Excretes about 65 grams P/day

Potassium excreted

Cow producing 20 litres milk/day

Excretes about 184 grams K/day

Total excreted per Lactation

Total, kg

Nitrogen 101

Phosphorus 17

Potassium 46

Most is deposited in the paddock; amount depends on the time in the paddock and yards.

Generally 10-15% in yards.

Total excreted per Lactation in yards

Total, kg Kg in the yards, 3 hrs/day

Nitrogen 101 13

Phosphorus 17 2

Potassium 46 6

What happens to the nutrients

Nitrogen Phosphorus Potassium

What happens to Nitrogen• 90% is in the liquid portion, 10% in the solids

50% is present as ammonia – easily lost

Organic forms, subject to changes:

Conversion to other organic forms

Mineralisation – to ammonium

Nitrification - to nitrite, then nitrate (needs oxygen)

Denitrification – to nitrous oxide then nitrogen

20-40% of N available in short term, residual 3 years

Nitrates easily leached (esp, urine patches)

Generally, 50% of the N in effluent is lost

What happens to Phosphorus

• Present in organic and inorganic forms

No losses from the effluent on treatment or

storage

Leaching only on coarse sandy soils

What happens to Potassium

• No losses from the effluent

Present in high levels in feeds (pasture 1.5% K)

Retained in clayey soils; leached from sands

Commonly high levels in paddocks close to the dairy

and effluent paddocks

High levels – contribute to health problems:

Calcium deficiency – milk fever

Magnesium deficiency – grass tetany

Potassium limits the rate of effluent application

Potassium sets the limit• Limit effluent to around a maximum of 100 kg/ha K

General rule, 1 hectare per 20 cows

Nutrient applications, at 1 ha/20 head

Cows producing 375 kg/ha MS

In yards 3 hours/day

Average pasture feed composition

No losses of Nitrogen

Total Kg/ha Fertiliser Kg/ha

Nitrogen 252 N 548 kg Urea

Phosphorus 42 P 467 kg Super

Potassium 114 K 228 kg Muriate

Manure Solids

Solids separators, material 10-30% DM P & K levels low N levels variable, around 0.3% on wet

basis (3 kg N/wet tonne) Value $20-$40/t wet. 90% of value is in the nitrogen

First pond sludgesN & P concentrations vary with depth in the pond

K more uniform.

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

0 500 1000 1500 2000

Depth

(m)

Nitrogen concentration against depth

0

0.5

1

1.5

2

2.5

3

3.5

4

4.5

0 50 100 150 200 250

Depth

(m)

Phosphorus concentration against depth

First pond sludges Dry matter, 6-8% N up to 1,700 ppm (1.7 kg/t wet) P 200 ppm (0.2 kg/t) K 600 ppm (0.6 kg/t) Value $4,100/ML ($4/1000 litres)

25 mm application (0.25 ML/ha) will apply:425 kg/ha N50 kg/ha P150 kg/ha K

Recommend 25 mm maximum application Most nutrient in organic forms, slow release

Economic value per head 13% of excreted nutrients are in the yard

Fertiliser equivalents (Urea, Super & Muriate).

If no N loss, $35/head/lactation

At 50% N loss, $27/head.

Value from the water in the effluent; at 50 L/head/day, value $5/hd.

Maximising nutrient response Apply the effluent nutrients when plants can respond:

when plants actively growingwarm & moist conditions

Victorian trial responses (3 years results)

Pasture response 9-16 kgDM/kg N applied Highest response in the year of application,

but response lasts 3 years.

Crop Response (tDM/ML)

Turnips 2.7 – 8.9

Pasture – silage regrowth 1.4 – 2.5

Risks of effluent application Nutrient accumulation in effluent paddocks – SOIL TEST

High levels – animal health problems

Contamination of surface water – runoff Avoid spreading in wet conditions

Contamination of groundwater More likely from ponds. Avoid waterlogged sandy soils.

Important points Useful amounts of N, P & K in effluents, potentially around

$35/head/lactation. Most value is the Nitrogen. N losses commonly 50%, lost as ammonia. Most nutrient value is in the liquid. Suggested maximum application rate is 1 ha per 20 cows; applies 252

kg/ha N, 42 kg/ha P, 114 kg/ha K (cows on yards 3 hrs/day) Avoid excessive application rates; K problems. Avoid applying to waterlogged soils. SOIL TEST application paddocks.

Effluent Management Code of Practice

TDIA prepared, November 2009

Expected to be gazetted soon

Part of the licence conditions to operate

a dairy

Effluent Management Code of Practice

Three requirements:

No effluent to leave the farm

Effluent management system in place

Land application to be sustainable

Effluent Management Plans

TDIA has developed a generic EMP.

Development and implementation will help to demonstrate compliance with the CoP.

ConclusionsA good effluent management system:

Utilises the nutrient content of effluent, worth $25-$35/head/year

Avoids pollution of surface and groundwater, and risks to animal health

Compliant with the industry Code of Practice