An assessment of the impact of Farming Rules for Water

The Farming Rules for Water (FRfW) were introduced in April 2018 to fulfil obligations on diffuse pollution under the Water Framework Directive, particularly in regard to reducing phosphorus (P) losses to water from agriculture. Rule 1 aims to ensure that ‘all reasonable precautions’ are taken to prevent diffuse pollution following the application of organic manures and manufactured fertilisers. To comply with Rule 1, farmers must demonstrate they have planned nutrient applications to ensure they are applied in quantities that are sufficient to meet, and not exceed, the crop and soil requirements (e.g. by using a recognized nutrient management system, such as RB209).

Compliance with the rules is managed by the Environment Agency (EA) and recent clarification of the interpretation of Rule 1 by the EA has confirmed that farmers must demonstrate that the timing and quantity of organic manure applied is in accordance with crop and soil need at the time of application. This applies to all types of organic manure containing readily available N (RAN), and effectively rules out autumn and winter applications except to a crop that has a nitrogen fertiliser requirement in those seasons (e.g. winter oilseeds and grass to support late season growth in August and September). The lack of an autumn window for applications of all livestock manures, biosolids, digestate and other organic materials which contain RAN is likely to have a significant impact on manure and nutrient management on all farms as in many circumstances it will not be practical to apply manure in spring. Moreover, a change in practice may also increase the risk of losses of pollutants other than nitrate (e.g. ammonia emissions to air, and P loss to water - so called ‘pollution swapping’). This impact assessment was commissioned to evaluate the impact of the EA’s interpretation of Rule 1 on farm practice and the wider environment.

Currently almost 50 million tonnes (MT) fresh weight of farm manures, 1.9MT compost, 4.3MT digestate (from commercial facilities) and 3.5 MT biosolids are applied to agricultural land in England on an annual basis. A large proportion of these – particularly the solid, low RAN materials (e.g. cattle and pig farmyard manure (FYM), biosolids and compost) are applied and incorporated in the autumn ahead of autumn-sown cereals. This impact assessment focused on livestock manures and a scenario was developed which only permitted their application in the autumn (August and September) to either winter oilseed rape and grass (i.e. crops with a nitrogen fertiliser requirement in the autumn, according to RB209 and NVZ rules). Using British Survey of Fertiliser Practice (BSFP) data, all other livestock manure applications in the months of August - November were moved to spring (February – April, to the same crop types). This resulted in the movement of c. 7 million tonnes of solid manures and 3 million m³ of slurry from autumn to spring, with spring slurry applications assumed to be applied using band-spreading equipment and solid manures broadcast and incorporated ahead of spring crops or top-dressed onto winter cereals.

Moving applications from autumn to spring poses several practical and logistical challenges to the management of organic materials, particularly associated with storage and spreading. For solid manures this is likely to result in an increase in the number of temporary field heaps and the time that the manure is stored in field. For slurries this will require an increase in the storage capacity of slurry tanks or lagoons. Where there is access to grass, it is likely that a minimum of 6 months storage will be required, however, where slurry is only applied to arable land at least 9 months storage is likely to be necessary. Moreover, ensuring that organic material applications are made to soils when they are strong enough to withstand the weight of spreading equipment, is an important practical consideration. Travelling on ‘wet’ soils with heavy spreading equipment is likely to cause significant compaction (with associated increased run-off and erosion), especially on clay and medium textured soils. The proportion of days in a month when medium textured soils are at or close to field capacity (i.e. ‘wet’) was estimated from 30 year average rainfall data (1981-2010) in order to assess the impact of application timing on soil compaction and run-off risk. In the summer and early autumn (May – September), when c.50% of solid manures and 35% of slurries are currently applied the risk of soil compaction and run off is low (soils at field capacity for <10% of month). By contrast, in February and March, soils are at field capacity for on average 70-80% of the month, and the number of available spreading days are significantly lower than in summer and early autumn. Moving the majority of autumn applications to spring will increase pressure on the number of days available for safe spreading (i.e. where the risk of soil damage or run-off is low), at a time when there is also a higher risk of soils returning to field capacity shortly after application.

A modelling approach was used to estimate changes in nitrate and phosphorus losses to water and ammonia and nitrous oxide losses to air (post storage) resulting from restrictions on the timing of applications required to meet the EA’s interpretation of Rule 1. Under current practice (baseline) the application of organic materials in England was estimated to result in annual ammonia volatilisation losses of 31kT NH₃-N, nitrate leaching losses of 9 kT NO₃-N and nitrous oxide emissions of 1kT NO₂-N, respectively. Baseline annual phosphorus losses from farm manure applications were estimated at 0.7kt P loss. Nutrient losses from manure applications were estimated to contribute c. 20% of the total ammonia emission, 2.5% of the total nitrate-N loss and 15% of the total P loss from all agricultural sources. The EA’s interpretation of Rule 1 was predicted to:

• reduce nitrate leaching losses by c. 60% (1.5% decrease in the total loss from agriculture)
• increase in ammonia emission by c. 10% (2% increase in total emissions from agriculture)
• increase P loss by c. 30% (5% increase in the total loss from agriculture)

The increase in ammonia emissions and P losses largely reflected the reduction in soil incorporation resulting from a change from applications to autumn stubbles to top-dressing to growing crops in spring. Increases in P losses are also exacerbated by applications to wet soils in the spring. Soil incorporation is an important mitigation method for controlling ammonia volatilisation to air and P losses to water via surface runoff/bypass flow. For livestock manures, these impacts are likely to be greatest in the East of England where most pig and poultry manures are applied ahead of autumn cropping.

The FRfW aims to prevent diffuse pollution following the application of organic manures and manufactured fertilisers, stating that materials should not be applied ‘if there is a significant risk of agricultural diffuse pollution’. This impact assessment has shown that the effective management of organic materials requires  consideration of the ‘balance of risks’ to  water, air and soil, as well as practical considerations, taking into account not only the type of organic material and when it is applied, but how and where it is applied. Autumn applications to light textured soils present the greatest risk of nitrate leaching. The risks of soil damage from spring applications is also lowest on light soils. By contrast ammonia losses to air and phosphorus losses to water pose the greatest pollution risk on clay and medium soils, and spring applications pose a significant risk of compaction on these soil types. Clay and medium soils also have more limited opportunities for spring cropping (and hence the potential for soil incorporation). Based on these findings, a matrix has been drafted, which aims to guide the industry on when and where organic materials can be used most effectively to reduce the risks that applications pose to diffuse water and air pollution and soil compaction.