Farmers put on a good spread
Paddy Johnson of ADAS discusses the effects of increased NVZs in England, the impacts on farmers and biosolids producers and help available to ensure compliance with the NVZ rulesBiosolids are a valuable source of readily available and slow-release nitrogen for crops. On many farms they make a valuable contribution in decreasing input costs and improving crop yields and quality. Biosolids suppliers commonly make applications at a rate of 250kg/ha of total nitrogen per annum.
Biosolids producers will be affected in other ways. Liquid digested sludge applications cannot be made to sandy or shallow soils in NVZs on land which is not in grass or to be sown to an autumn crop between August 1 and November 1. This is because these sludges have high available nitrogen contents and without any crop present much of this nitrogen will be lost by leaching. If an autumn crop is to be sown the closed-period starts on September 1. It is only materials with high available nitrogen contents that have closed-period restrictions and only on sandy or shallow soils. The timing of biosolids applications low in available nitrogen materials, e.g. digested and lime stabilised cakes and thermally dried granules, is not affected by the NVZ rules.
In NVZs the farmer will need to keep records of the timing of application, type of material and the amount of total nitrogen applied. Farmers will also have to keep within a total organic nitrogen loading for the whole of the farm, based on different limits for arable and grass areas, which will create competition for the landbank from all organic materials that are recycled to land. Full details of how to calculate the nitrogen capacity of a farm will be supplied by DEFRA to every farmer in an NVZ, in a booklet Guidelines for Farmers in NVZs – England (similar documents will be available in Wales, Scotland and Northern Ireland).
Once biosolids have been applied, the farmer has to ensure the nitrogen which will become crop-available is taken into account when deciding how much manufactured fertiliser nitrogen to apply. This will be something all people in the biosolids supply industry, who deal with farmers, will need to know about. One form of help for this is the decision support system MANNER, available free from ADAS. Applications of organic manures should not be made which would supply more nitrogen than the following crops require. The NVZ rules make the application of organic manures on flooded, waterlogged, snow covered or frozen ground illegal. They also make application within 10m of a watercourse illegal. But these are requirements of the DEFRA Water Code which biosolids suppliers will have been conforming to for many years. There are other NVZ rules that suppliers should be aware of which are explained in the guidelines booklet.
In summary, the main impacts of the NVZ rules for biosolids suppliers are likely to be the need to limit field application rates to 250kg/ha total nitrogen per annum and increased competition from other organic wastes and livestock manures. The greatest impact is likely to be in mixed farming areas and areas where there is a concentration of intensive livestock, such as pigs and poultry holdings. The rules will also increase the need for field staff to be qualified fertiliser advisers. Many of the requirements are good practice measures already being followed by biosolids suppliers. The closed periods introduced under the NVZ rules will impact on liquid operations in particular. The timing of cake and granule applications will be unaffected by these changes. Definitive maps will be available shortly and suppliers should review their application rates and assess whether there is any potential impact on their available landbank