ARCHIVE: Fertiliser Manual (RB209)

Livestock manures


Manure management planning

It is essential to plan the handling and use of manures on a farm. This will ensure that good use is made of the nutrient content (‘content’ is used rather than the more accurate ‘concentration’ as this is common usage) of the manures and that the risks of causing environmental pollution are minimised. The Code of Good Agricultural Practice (Defra, 2009) provides guidance on how to prepare a Manure Management Plan (see Defra Manure Management Plan – a step by step guide for farmers). This plan includes a field risk assessment which will help in deciding when, where and at what rate to apply solid manures, slurry and dirty water, thereby reducing the risks of causing water pollution and transfer of pathogens to water. In NVZs, the preparation of a field risk assessment is a requirement of the Action Programme (NVZ Guidance Leaflet 8).

When planning manure management systems, information is needed on the quantity and nutrient content of livestock manures produced on a farm. This depends on a number of factors, including the number and type of livestock, the diet and feeding system, the volume of dirty water and rainwater entering storage facilities, and the amount of bedding used. Although the volume of manure to be managed will vary considerably with the amount of water introduced into the system (often doubling the volume of slurry to be handled), estimates of the quantities of excreta produced by livestock are useful for calculating manure storage needs, and manure nutrient contents (ex housing and storage) for nutrient planning at the farm level. The table below shows typical outputs of undiluted excreta and nutrient outputs (ex housing and storage) for selected livestock types. In NVZs, it is a mandatory requirement to have 26 weeks storage capacity for pig slurry and poultry manure, and 22 weeks storage capacity for all other livestock slurries (NVZ Guidance Leaflet 4).

Estimated quantities of excreta and nutrient outputs at the end of the housing/storage period.

 

Type of livestock

Age, Liveweight or Milk yield

Housing period
or occupancy % of year

Output at end of housing/storage period         

        

Undiluted excreta

Nitrogen (N)d

Phosphate (P2O5)d

Potash (K2O)e

     

(t or m3)

(kg)

(kg)

(kg)

Cattle            

Dairy cow

> 9000 litres

60a

14.0

69b

31

56

 

6-9000 litres

60a

11.6

60b

26

46

 

< 6000 litres

60a

9.2

46b

20

37

Dairy heifer replacement

13 months to first calf

50

7.3

30b

12.5

29

Beef suckler cow

> 500 kg

50

8.2

41b

15.5

33

 

< 500 kg

50

5.8

30b

12

23

Beef cattle

13-25 months

50

4.7

25b

7.9

19

 

3-13 months

50

3.6

17b

5.0

15

Pigs

 

 

 

 

 

 

1 sow + litter

Litter up to 7 kg

100

4.0

18

13.5

14

Finishers (dry-meal fed)

7-13 kg

71

0.34

1.0

0.34

1.2

 

13-31 kg

82

0.6

4.2

1.8

2.1

 

31-66 kg

88

1.2

7.7

3.9

4.2

 

66+ kg

86

1.6

10.6

5.6

5.6

Poultry

 

 

 

 

 

 

1000 laying hens (caged)

17 weeks & over

97

41

400

350

390

1000 Broilers

 

85

19c

330

220

340

1000 Turkeys (male)

 

90

53c

1230

1020

950

1000 Turkeys (female)

 

88

39c

910

740

690

1000 Ducks

 

83

30c

730

760

230

a. ‘housing period’ for dairy cows includes allowance for time spent in yards/buildings during milking in the grazing season.
b. N.B. These values should NOT be used for calculating NVZ compliance as they do not include excretal N deposited in the field during grazing.
c. excretal output includes litter, where appropriate.
d. nitrogen and phosphate outputs based on nutrient balance estimates.
e. potash outputs based on estimated undiluted excreta volumes and typical potash content of manures (@10% dry matter content for slurries).

Nutrient content of manures

For nutrient management planning, it is important to know the nutrient content of manures applied to land. The tables on pages 62-69 give typical values of the total nutrient content of manures based on the analysis of a large number of samples.

Owing to farm-specific feeding and manure handling practices, manures produced at a particular livestock unit may have a nutrient content that is consistently different from the values given in the tables. It is therefore worthwhile having the nutrient content of representative manure samples determined by analysis. Rapid on-farm kits (e.g. Agros, Quantofix) can reliably assess the ammonium-N content of slurries (and it is this value that should be entered into the ammonium-N input box on the MANNER-NPK analysis screen), but laboratory analysis is necessary for other nutrients. Laboratory analyses should include dry matter (DM), total N, total P2O5, total K2O, total SO3, total MgO and ammonium-N (NH4-N).

Additionally, nitrate-N (NO3-N) should be measured for well composted FYM and poultry manures and slurry that has been treated aerobically, and uric acid-N for poultry manures. Hydrometers can be used to measure slurry dry matter content and, where dry matter varies, to estimate nutrient analyses by adjusting previous laboratory results or the typical values in the cattle (page 65-67) and pig slurry (page 67-69) tables. Appendix 6 provides information on the calculation and interpretation of laboratory manure analysis results.

It is important that sampling is carried out carefully and that representative samples are provided for analysis (see Appendix 6 for guidance on sampling). The optimum sampling frequency will vary depending on how manures are managed on the farm, but at least two samples per year are recommended coinciding with the main spreading periods.

Whether using typical values for the nutrient content of manure, or the results of analysis, the availability of the nutrients for crop uptake must be assessed before the fertiliser replacement value of a manure application can be calculated. Values for the availability of manure nutrients from different application timings and methods have been determined from detailed research studies.

Principles of nitrogen supply and losses

Nitrogen is present in manures in two main forms:

  • Readily available nitrogen (i.e. ammonium-N as measured by N meters, nitrate-N and uric acid-N) is the nitrogen that is potentially available for rapid crop uptake. Slurries and poultry manures are ‘high’ in readily available-N (typically in the range of 35-70% of total N) compared with FYM which is ‘low’ in readily available-N (10-25% of total N) – see diagram below.
  • Organic-N is the nitrogen contained in organic forms which are broken down slowly to become potentially available for crop uptake over a period of months to years.

Crop available nitrogen is the readily available-N that remains for crop uptake after accounting for any losses of nitrogen. This also includes nitrogen released from organic forms.

Following the application of manure to land, there can be losses of nitrogen by two routes. Ammonium-N can be volatilised to the atmosphere as ammonia gas. Following the conversion of ammonium-N to nitrate-N, further losses may occur through nitrate leaching and denitrification of nitrate to nitrous oxide and nitrogen gas under warm and wet soil conditions. To make best use of their nitrogen content, organic manures should be applied at or before times of maximum crop growth – generally during the late winter to summer period.

Ammonia volatilisation

Around 40% of the readily available nitrogen content of manures is often lost following surface application to land. Ammonia loss and odour nuisance can be reduced by ensuring that manures are rapidly incorporated into soils (within 6 hours of application for slurries and 24 hours for solid manures to tillage land). For slurries, shallow injection and band spreading techniques are effective application methods that reduce ammonia emission (typically by 30- 70%) compared with broadcast application. Also, slurry band spreading (trailing shoe and trailing hose) and shallow injection application techniques increase the number of spreading days, and cause less sward contamination than surface broadcast applications. These practices will also increase the amount of nitrogen available for crop uptake. Ammonia losses are generally smaller from low dry matter slurries because they more rapidly infiltrate into the soil. Higher dry matter slurries remain on the soil/crop surface for longer leading to greater losses. Losses are also higher when slurries are applied to dry soils under warm weather conditions.

On large pig and poultry units that are permitted under regulations that implement the EU Integrated Pollution Prevention and Control (IPPC) Directive, there is a requirement where solid manures are applied to uncropped land or bare soil to incorporate them into the soil within 24 hours, unless such applications are used to control wind erosion on susceptible soils. Slurry can be applied by an injector, or band spreader, or by any type of splash plate spreader provided slurry is incorporated into the soil within 6 hours of application and provided such equipment is operated to avoid slurry atomisation. Slurry may also be applied by irrigation equipment provided it is applied to a growing crop and such equipment provides a low spreading trajectory (operated at low pressure to create large droplets). If dilute pig slurry (less than 2% dry matter) is applied by irrigation equipment then it does not have to be to a growing crop.

Nitrate leaching

The amount of manure nitrogen leached following land application is mainly related to the soil type, the application rate, the readily available-N content and the amount of rainfall after application. As ammonium-N is rapidly converted in the soil to nitrate-N, manure applications during the autumn or early winter period should be avoided, as there is likely to be sufficient over-winter rainfall to wash a large proportion of this nitrate out of the soil before the crop can use it. Delaying applications until late winter or spring will reduce nitrate leaching and increase the efficiency of utilisation of manure nitrogen. This is particularly important for manures with a high content of readily available-N. In NVZs, there are mandatory closed spreading periods for high readily available-N manures (e.g. slurries, poultry manures), which typically have greater than 30% of their total nitrogen content present as readily available N (see Defra Guidance for Farmers in Nitrate Vulnerable Zones, Leaflet No. 8 Field application of organic manures).

 Release of crop-available nitrogen from organic nitrogen

The organic nitrogen content of manures is released (mineralised) slowly over a period of months to years. Where the nitrogen mineralised from the manure is not taken up by the crop in the season following application, nitrate may be lost by leaching during the following overwinter period, or can accumulate in soil organic matter allowing further long-term savings in nitrogen fertiliser inputs. Around 5% of the total nitrogen content of manures may become available for the second crop following application.

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