How to make the most of poultry manure: phosphate – part 2
The UK consumes a significant quantity of poultry products each year. For example:
In my last blog, we focused on its nitrogen contribution and how best to manage its supply. This blog focuses on the phosphate and potash contribution poultry manure can supply and, in the case of phosphate, how excess in the environment can cause issues with water quality.
Like nitrogen, poultry manure is a rich source of phosphate. When planning manure applications, this rich supply must be considered from both a soil and agronomic need perspective and an environmental risk perspective. Poultry manure and its return to land can ignite debate, mainly with the risk of phosphate causing damage to the water environment through eutrophication and habitat loss.
Excess nutrients, especially phosphate, reduce the diversity of aquatic plants. This has knock-on impacts on aquatic invertebrates, fish, and other organisms living in the river. Excess nutrients also cause algal blooms during high temperatures or low flow periods (or both), driving down biological oxygen levels and causing harm to salmon and other fish species.
The River Wye Action Plan and environmental incentives for farmers
For several years, the River Wye catchment has been under significant pressure from agricultural pollution due to unsustainable farming practices, the concentration of poultry units in the area, and other pressures from sewage discharges. Defra reports that phosphate enters the river catchment from the following:
In the spring of 2024, Defra announced the River Wye Action Plan, which involves nine commitments to support the ongoing local efforts to restore it fully in the long term. This plan aims to prevent the catchment’s decline by making it a pilot for transforming how manure is managed while continuing to support the creation of new habitats to keep nutrients and sediment in the field and make space for nature. This plan will also help further progress towards legally binding environmental targets on species abundance and water pollution.
One of the nine Defra commitments includes £35 million for poultry manure combustors (PMC). When poultry manure is burnt, a nutrient-rich ash is produced. This material remains a valuable phosphate-containing fertiliser that is easier to transport to other farms in the catchment. The burning process causes the nutrients to become less mobile, which means the ash poses less of a risk to the environment when applied. The combustion units can also lower a farm’s energy consumption by recycling the heat energy generated during the burning process for use on the farm.
Defra plans to work with farmers and stakeholders in the Wye to determine the best way to deliver the funding to trial PMCs and understand the distances and costs of transporting the ash to avoid overapplication within the catchment.
The government has also launched the Sustainable Farming Incentive (SFI), which provides funding for farmers and landowners to transition to farm practices that encourage better land management. The 2024 SFI scheme has 102 actions, and many options include activities around soil health, its management and long-term improvement.
NRM data analysis of poultry manure: phosphate and potash
The charts below (figures 1 and 2) describe the variation in phosphate and potash concentrations measured in poultry manures with 20, 40, 60, and 80% dry matter (DM) content. On average, the measured phosphate values are higher than the comparative typical values (see Table 1 below), apart from 60% DM, which is slightly lower. However, as we expect, there is a wide range, which increases as the dry matter of the poultry manure increases.
For example, in manure with 60% DM content (figure 1c), the median is slightly skewed toward the 25th percentile value, where a quarter of the samples analysed contained just less than 10kg P2O5/t. The typical average value in RB209 is 17kg P2O5/t, whereas this data suggested an average value of 15.4kg P2O5/t.
The median value describing the phosphate concentration of 40% DM (Figure 1b) was also skewed towards the 25th percentile. Still, the median was incredibly close to the typical average value (11.9 V 12kg P2O5/t). The average content was 14.1 kg P2O5/t, indicating that more samples had a greater concentration than the average published in RB209.
The phosphate contents at 80% DM (figure 1d) were more normally distributed, as indicated by the median value being very close to the average value. However, the average value measured was lower than the typical values published in RB209 (see table 1 below).
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The potash content measured in poultry manure of all dry matter contents was more normally distributed, but in all cases (20, 40, 60, 80% DM), the average values were less than the typical values published in RB209.
It’s important to understand the amount of phosphate & potash contained in poultry manure for several reasons. The main reasons are:
It is also important to realise that if you apply poultry manure at its maximum allowable field rate of 250kg N/ha, soil phosphate and potash can easily build up to unsustainable levels.
For example, if we apply an 80% DM poultry manure (which contains on average 30kg/t of total nitrogen at a rate of 8.3t/ha to supply 250kg N/ha), this means we would be applying on average 152kgs of total and 92kgs of available phosphate and 194kg/ha of total and 175kgs of available potash. If these rates are applied consistently over time, it is easy to see how soil indices can quickly build up as crop growth is unlikely to remove all the phosphate and potash applied in one or even two years.
Keeping nutrients in the field, where crops can effectively utilise them, is more achievable when we measure the nutrient content before application. Understanding how nutrient-rich these materials are allows us to use them optimally, reducing our spending on inorganic fertilisers and potentially exporting them to farms in greater need of nutrients. This awareness enables us to plan more effectively and manage resources efficiently, particularly in the case of phosphates, which we must keep out of our water systems.
How NRM can help
NRM provides a range of analytical services to help you get the most out of your livestock and organic manures. With accurate, timely data on manure nutrient content, you can make informed decisions on application rates, saving on fertilisers and boosting productivity.
To understand more about how analysis can help, contact your advisor or speak to us directly. You can also request sampling supplies on our website here.
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