ARCHIVE: Fertiliser Manual (RB209)

Using farm manures and fertilisers together

 


 

A planned and integrated manure and inorganic fertiliser policy aims to utilise as much as possible of the nutrient content of manures. Failure to adequately allow for these nutrients, particularly nitrogen, not only wastes money because of unnecessary fertiliser use but can reduce crop yields and quality – e.g. lodging in cereals, poor fermentation in grass silage and low sugar levels in beet.

  1. Calculate the quantity of crop available nutrients (equivalent to fertiliser) supplied by each manure application.
  2. Identify the fields that are available and that will benefit most from the application of manure. This will need to take account of the accessibility and likely soil conditions in individual fields at the time of application, and the application equipment that is available. Crops with a high nitrogen demand should be targeted first. Fields at low soil P or K Indices will benefit more than those at high Indices.
  3. Plan the application rate for each field ensuring that no more than 250 kg/ha total organic manure nitrogen is applied in any 12 month period – it is mandatory in NVZs not to exceed this amount. Also, take account of the phosphate content of manures over the crop rotation to avoid excessive enrichment of soil phosphorus levels. Make sure that the plans adhere to the NVZ rules in England and Wales. As far as possible, apply manures in the late winter to summer period – this will make best use of the nitrogen content.
  4. Aim for the manure application to supply no more than 50-60% of the total nitrogen requirement of the crop, with inorganic fertiliser used to make up the difference. This approach will minimise the potential impact of variations in manure nitrogen supply on crop yields and quality.
  5. Make sure that manure application equipment is well maintained and suitable for applying the manure in the most effective way, minimising losses of ammonia-N and soil or crop damage. The equipment should be routinely calibrated for the type of manure being applied, using the guidelines contained in Booklet 3 of the Managing Livestock Manures series.
  6. Following application, use the tables in this section or the MANNER-NPK / PLANET decision support systems to calculate the amount of crop available nitrogen supplied from each manure application in each field. Also, use the tables in this book to calculate the amounts of phosphate, potash, sulphur and magnesium applied.
  7. Calculate the nutrient requirement of the crop, then deduct the nutrients supplied from manures. This will give the balance that needs to be supplied as inorganic fertiliser (see examples 1 and 2 below).

Practical aspects of manure use

  • Manures are commonly applied to arable stubbles in the autumn prior to drilling winter cereals. But to make best use of manure nitrogen and to minimise nitrate leaching losses, manures should, if possible, be applied in the late winter to summer period. Band spreaders and other equipment are now available that allow accurate slurry top-dressing across full tramline widths, without causing crop damage. An
    additional benefit of band spreading is that ammonia emissions are reduced by 30-40% compared with conventional ‘splash-plate’ surface application, along with odour nuisance.
  • Manure applications before spring sown crops (e.g. root crops, cereals and oilseed rape) should be made from late winter onwards to minimise nitrate leaching losses, particularly where high readily available N manures are applied. In NVZs, applications of organic manure with a high readily-available nitrogen content (e.g. slurry, poultry manure and liquid digested sludge) can be made from 1st January onwards on sandy/shallow soils and 16th January onwards on all other soils. Rapid soil incorporation
    on tillage land (e.g. within 6 hours following surface broadcast application) will minimise ammonia losses and increase manure crop available nitrogen supply.
  • Manure applications to grassland are best made to fields intended for silage or hay production. Cattle slurry and FYM contain large amounts of potash relative to their readily available nitrogen and total phosphate contents, and are ideally suited to this situation. Solid manure application rates should be carefully controlled to avoid the risk of sward damage and contamination of conserved grass with manure solids, which can adversely affect silage quality. To encourage a low pH and good fermentation, grass cuts following solid manure or late slurry applications should be wilted before ensiling, or an effective silage additive used. To make best use of slurry nitrogen, applications should be made in the late winter to spring period. Slurry applications in summer are likely to be less efficiently utilised because of higher ammonia losses. The use of band spreading and/or shallow injection (5-7 cm deep) techniques will reduce ammonia-N losses (typically by 30-70% compared with surface broadcast application) and herbage contamination.
  • Where slurry and solid manure applications are made to grazed grassland, the pasture should not be grazed for at least 4 weeks following application, or until all visible signs of slurry solids have disappeared. This will minimise the risk of transferring disease to grazing livestock. Also, take care to ensure that the manure potash supply does not increase the risk of grass staggers (hypomagnesaemia) in stock through reduced herbage magnesium levels.
  • Forage crops, particularly forage maize prior to drilling, provide an opportunity to apply manures in late spring. Manure application rates should be carefully controlled and where possible the manure should be rapidly incorporated into the soil to minimise ammonia-N emissions and odour nuisance. Care should be taken to ensure that such applications do not lead to very high contents of crop-available phosphate
    in the soil.
  • Where manure applications are made before “ready to eat crops” i.e. crops that are generally not cooked before eating, relevant industry guidance should be followed to minimise the risks of pathogen transfer.

Example 1.

30 m3/ha of cattle slurry (6% dry matter) is broadcast in early spring before first-cut silage. The soil is at P Index 2 and K Index 2-. Where the slurry is surface broadcast in the spring, allowing for manure nutrients saves up to £95/ha. This potential saving will be less following autumn or winter application, or where soil P or K Indices are above maintenance levels.

 

 

Nitrogen (N)

Phosphate (P2O5)

Potash  (K2O)

Financial Saving (£/ha)

1. Estimated total nutrients in slurry (kg/m3)

 

 

 

 
Analysis of representative sample or typical values from tables in this booklet. 2.6 1.2 3.2  
2. Estimate available nutrients in slurry (kg/m3)        
Nitrogen (table on page 64)

 0.9a

     
Phosphate and potash (table on page 65)

  

 0.6

 2.9

 
3. Nutrients supplied by slurry that are equivalent to inorganic fertiliser (kg/ha)        

30m3/ha supplies 78 kg/ha total N and 27 kg/ha crop available N

 27

 36b

 96b

 
Potential saving from manure use      

 £95/had

4. Nutrient requirements for first-cut silage to produce a yield of 10 t/ha (kg/ha)        
Section 8 of this book

 120

 40c

 80c

 
5. Inorganic fertiliser needed for the silage crop (kg/ha)        
Stage 4 minus Stage 3

 93

 4

 NIL

 
Actual saving for next crop from manure use      

 £85/ha

6. Surplus manure nutrients for subsequent crops that are equivalent to inorganic fertiliser (kg/ha)        
Stage 3 minus Stage 4  

NIL

16

 
Saving for subsequent crops from manure use      

£10/ha

a. Nitrogen availability is 35% of total N (see table on page 64)
b. Total phosphate and potash content used in calculations to maintain soil Indices.
c. Nutrients required for spring application (soil P Index 2 and K Index 2-)
d. Saving for next crop plus value of surplus manure phosphate and potash which will contribute to the nutrient requirement of future crops.
Assumed fertiliser costs: Nitrogen 60p/kg; phosphate 60p/kg; potash 60p/kg

Example 2.

35 t/ha of pig FYM is applied in autumn to a clay soil before drilling winter wheat (8 t/ha grain yield, straw baled). It is NOT rapidly incorporated. The soil is at P Index 2 and K Index 2-. Where the FYM is surface applied in the autumn, allowing for manure nutrients saves up to £309/ha. This potential saving will be less where soil P or K Indices are above maintenance levels.

 

 

Nitrogen (N)

Phosphate (P2O5)

Potash (K2O)

Financial Saving (£/ha)

1. Estimated total nutrients in FYM (kg/t)

 

 

 

 
Analysis of representative sample or typical values from table on page 64.

 7.0

 6.0

 8.0

 
2. Estimate available nutrients in FYM (kg/t)        
Nitrogen (table on page 64)

 0.7a

     
Phosphate and potash (table on page 65)

   

 3.6

 7.2

 
3. Nutrients supplied by FYM that are equivalent to inorganic fertiliser (kg/ha)        

35m3/ha supplies 245 kg/ha total N and 25 kg/ha crop available N

 25

 210b

 280b

 
Potential saving from manure use      

 £309/had

4. Nutrient requirements for winter wheat (kg/ha)        
Section 4 of this book

220

 70c

 85c

 
5. Inorganic fertiliser needed for the wheat crop (kg/ha)        
Stage 4 minus Stage 3

195

 NIL

 NIL

 
Actual saving for next crop from manure use      

 £108/ha

6. Surplus manure nutrients for subsequent crops that are equivalent to inorganic fertiliser (kg/ha)        
Stage 3 minus Stage 4  

140

195

 
Saving for subsequent crops from manure use      

£201/ha

a. Nitrogen availability is 10% of total N (see table on page 64)
b. Total phosphate and potash content used in calculations to maintain soil Indices.
c. Nutrients required for spring application (soil P Index 2 and K Index 2-)
d. Saving for next crop plus value of surplus manure phosphate and potash which will contribute to the nutrient requirement of future crops.
Assumed fertiliser costs: Nitrogen 60p/kg; phosphate 60p/kg; potash 60p/kg

Manure Application

It is important that manures are applied evenly and at known application rates. The most important causes of uneven application on farms are the incorrect setting of bout widths and poor attention to machinery maintenance. For both slurries and solid manures, the evenness of spreading is usually better with rear discharge spreaders than side discharge machines. Top-dressing slurry to arable crops in spring can be carried out using tankers or umbilical systems, with boom applicators (fitted with nozzles or trailing-hoses) operating from tramlines. The aim should be to apply all manure types evenly with a coefficient of variation of less than 25%. This is achievable with many commonly used types of manure application equipment provided they are well maintained and calibrated.

Application rates can be calculated simply from a knowledge of the capacity of the slurry tanker or solid manure spreader (by weighing both full and empty machines on a weighbridge), the number of loads applied per field and the field area. An accurate flow meter should be used to measure the slurry application rate of umbilical and irrigation systems. More information about manure spreading systems is in Booklet 3 of the Managing Livestock Manures series (see Section 9).


Heavy metals

Livestock manures also contain heavy metals, which on certain soils, for example copper deficient soils, can correct micronutrient (trace element) deficiency. However, in the majority of situations, the accumulation of heavy metals in soil is the more important issue. Pig and poultry manures can contain elevated levels of zinc and copper, which in the long-term (over 100 years), may lead to undesirably high soil levels. Where pig or poultry manures have been applied to land for a number of years and will continue to be applied, it is advisable to sample the soil periodically for analysis for heavy metals.

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