Sludge Regulations 1989

These regulations enact the European Directive (on the protection of the environment, and in particular of the soil, when sewage sludge is used in agriculture, 86/278/EEC). This was the first soil protection directive. The main provisions of the 1989 Regulations require that:

• All soils must be sampled and the results must be available before the first application of biosolids, and be resampled thereafter when heavy metals could have accumulated.
• Biosolids must not be applied to agricultural land when the concentrations of certain heavy metals in the soil (lead, cadmium, mercury, copper, zinc, and nickel) are greater than specified limits, according to soil pH.
• The rate at which heavy metals in biosolids may be added to soil is restricted.
• Biosolids must not be applied if the soil pH is below 5.0.
• Restrictions on use of different materials and harvest intervals for different crops must be adhered to, see Safe Sludge Matrix, page 3.
• Biosolids application rates must take account of the fertiliser needs of the rotation; the use of biosolids must not impair soil quality nor pollute ground or surface waters.

The farmer or landowner must provide the biosolids producer/supplier with relevant information about the application of other materials to the land. The biosolids producer/supplier must provide information to the farmer or landowner about the nutrients and heavy metals applied in the biosolids.

Cross-compliance

Statutory Management Requirement No. 3 (SMR 3) requires compliance with the Sludge (Use in Agriculture) Regulations 1989 and the Code of Practice for Agricultural Use of Sewage Sludge. HMSO, London 1996. The biosolids supplier will ensure that SMR 3 is observed and also SMR 4 (Nitrate Vulnerable Zones), as far as biosolids are concerned.

Use of biosolids can be considered to contribute to the requirement to maintain the land in ‘Good Agricultural and Environmental Condition’ (GAEC) because it improves soil structure, builds soil organic matter and increases water infiltration rate and resistance to soil erosion.

Stakeholder agreement

In the latter part of the 1990s, ADAS facilitated discussions between the British Retail Consortium, Country Land and Business Association, Environment Agency, National Farmers’ Union, Department of Environment Transport and Regions, Ministry of Agriculture Fisheries and Food, Water UK and other stakeholders to review the Regulations and agree additional requirements that would enable the use of biosolids on farmland to be welcomed by all parties as part of sustainable development. The Agreement on the method of working came into force on 31st December 1998. All agreed that the existing Regulations dealt with chemical risks adequately. Measures were agreed to further control the risk of disease transmission compared with the Regulations. Sludge treatment was to be based on HACCP (Hazard Analysis and Critical Control Point) principles, with two classes of treated sludge and defined rules on how they could be used. With this additional control and with FACTS training for advisors, all parties agreed that using biosolids to complete nutrient cycles and conserve organic matter is part of sustainable development. Conservation and recycling of phosphate by using biosolids to complement mineral fertiliser is especially relevant to sustainability; the phosphate industry estimates that the world’s reserves will be exhausted in between 100 and 300 years at the current rate of exploitation, depending on price.

The agreement was published by ADAS as the ‘Safe Sludge Matrix’; it affects all applications of biosolids to agricultural land. Defra planned to revise the Sludge Regulations to embembody the provisions of the Agreement and published a consultation in 2001, but revision now looks unlikely.

The Agreement on sludge treatment is:

Untreated sludge

Not permitted on land for food crops since 1999, nor for non-food crops since 2005.

Conventionally treated biosolids

These are biosolids that have undergone biological, chemical or heat treatment to reduce the fermentability and possible health hazards. The commonest treatment is anaerobic digestion. Conventional treatment ensures that at least 99% of pathogens have been destroyed.

Enhanced treated biosolids

These are biosolids subjected to treatment that virtually eliminates any pathogens. These materials will be free from Salmonella and the treatments will destroy 99.9999% of all pathogens.

The Safe Sludge Matrix

All applications must comply with Sludge (Use in Agriculture) Regulations and Defra Code of Practice for Agricultural use of Sewage Sludge.
Applications not allowed (except where stated conditions apply

Grass & Forage (deep injected or ploughed down only)3 week no grazing and no harvest interval applies 3 week no grazing and no harvest interval applies

Food Crops		Conventionally treated biosolids		Enhanced treated biosolids
Fruit
Salads			(30 month harvest interval applies)		10 month harvest interval applies
Vegetables			(12 month harvest interval applies)
Horticulture
Combinable & Animal feed crops
	– Grazed
Grass & Forage		(deep injected or ploughed down only)	3 week no grazing and no harvest interval applies		3 week no grazing and no harvest interval applies
	– Harvested
		(No grazing in season of application)
Industrial Crops
Industrial oilseed rape
Linseed
Flax
High erucic acid rape (HEAR)
Hemp for fibre
Coppice and other biomass crops
Other industrial crops

Matrix cropping categories

Best fertiliser practice

Nitrogen

Best fertiliser practice requires nitrogen (N) to be applied to an economic optimum level with timing matched to plant growth so that risk of N loss to the environment is minimised. Excess nitrogen carry-over should be avoided.

The Code of Good Agricultural Practice for the Protection of Water (1998) recommends a limit on the amount of total nitrogen to be applied in biosolids and other organic manures to no more than 250 kg/ha/year. Sludge cake which contain little available N may be applied at rates up to 500 kg/ha of total N in one application every two years in catchments less sensitive to nitrate leaching.

More stringent limits apply in NVZs – at the field level it is not permitted to apply more than 250 kg/ha total nitrogen per year. Also, full allowance should be made crop-available nitrogen supply from biosolids when calculating how much inorganic fertiliser N (if any) a crop needs.

Phosphate and Potash

The principles are quite different to those for nitrogen.

Best practice requires the maintenance of acceptable levels of these nutrients in the soil on a long-term basis. Fertiliser applications should aim to raise soil phosphorus (P) and potassium (K) to such levels that no further economic response occurs, and then to maintain these levels in the soil by replacing the nutrients removed in harvested crops.

At soil P Index 3 phosphate additions (biosolids or fertilisers) should not exceed crop offtake over the rotation. For most crops no phosphate is recommended at Index 4 or above, but biosolids may be applied, taking care to minimise the risk of run-off, soil erosion or leaching.

Nitrogen and potash balance

N and K are essential partners. If potash is limiting, the crop will not respond fully to nitrogen thus penalising yields and product quality. Biosolids can provide large quantities of nitrogen which must be balanced with adequate potash to ensure its efficient use.

Inefficiencies of N uptake and use in the plant may result in significant losses of N to the environment if potash levels are deficient.

Visual symptoms of P and K deficiency

Do not rely on visual symptoms in a crop to determine the adequacy of potash or phosphate supply. Deficiency symptoms are easily confused with other problems, frequently appear too late for damage to be prevented or may be totally absent despite yield/quality penalties.

The best way to ensure the maintenance of adequate soil fertility is to apply nutrients to replace those removed by cropping, and to monitor soil reserves by regular analysis every 4-5 years.

Potash and profit

Unlike many factors, potash fertility is within a farmer’s control and it is unwise to allow low reserves of this relatively inexpensive input to prejudice crop performance.

The penalty from inadequate potash will depend upon the soil type, the crop and the growing conditions. Even with so-called ‘less responsive’ crops such as cereals or grass the effects can be large.

Nutrient uptake

Typical uptake for cereal crops

Arable

For arable crops the typical uptake pattern of major nutrients is shown in the graph. Relatively small amounts of nutrient are required during the establishment period, but such supplies are vital to the development potential of the crop. Daily uptake increases dramatically during vegetative growth and restriction of nutrient supply at this stage can critically affect final yield and product quality such as grain sample, tuber size and numbers, sugar content etc. Peak uptake for potash is around flowering time for most combinable crops and at the end of the growing season for root crops. Peak uptake for nitrogen and phosphate coincides with the end of season.

Typical potash uptake and removal for high yielding crops

Plants must be able to take up nutrients when required at the rate to match potential growth. The total supply must provide for peak uptake rather than just the quantity removed at harvest. These can be very different especially for potash.

Grass and forage crops

With grazing, the livestock are continuously re-cycling nutrients back to the soil via dung and urine so replenishment needs are low. However hay and silage are similar to the arable situation – but more so!

Grassland conservation removes the whole crop, possibly several times a season, thus both uptake and removals of potash can be very large.

Typical K₂O removal in cut grass forage crops

Timing of application of potash

Additional potash requirements for crops receiving biosolids

For average-yielding crops assuming no other manure is applied
Fertiliser policy should be tailored to individual situations taking into account: rotation, crop grown, yield, treatment of residues such as straw, soil type and soil fertility level. Refer to other PDA leaflets or to the MAFF RB209 recommendations for precise guidance for individual crops. Check soil nutrient status every 4-5 years by soil analysis.

Conclusion

The application of biosolids to agricultural land makes a useful contribution to the recycling of nitrogen and phosphate, and completes natural carbon cycles. However, biosolids are seriously imbalanced nutritionally because of their low potash content. Where they are used additional potash is required and there is frequently only a need to apply a straight potash fertiliser to balance the N and P in the biosolids. Serious soil fertility and crop yield problems will usually arise if this balancing potash is omitted. Potash is firmly held in most soils so there is considerable flexibility in timing the applications of this essential nutrient. (see Timing of Potash)