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SMART-P™ granulated compound fertilisers
Nutrient recycling for sustainable biosolids management
(PRELIMINARY)
1.1 Introduction
Biosolids have been used safely in agriculture worldwide for over forty years. They contain a range of plant-available and soil-extractable nutrients useful in agriculture. Their use improves soil structure, drainage and available water capacity and so benefits agriculture (excerpt from the Recycling of Biosolids to Land, Water UK, March 2006).
The management of biosolids is particularly challenging for several reasons. Firstly, the nutrient content is highly variable coupled with a less controllable release characteristic that makes crop yield planning very complex. The traditional approach of applying the product according to the N content invariably leads to soil accumulation of phosphorus, a particular concern in many areas with watercourses sensitive to eutrophication. Transportation, storage and spreading of the bulky cake products also prove to be a disincentive for many operators. New uncertainty about the possible re-growth of the pathogen indicator E. coli suggests that recycling cost may rise further to account for additional treatment and quality assurance.
Organo Mineral Fertiliser (OMF) is a new approach to biosolids management that promises to alleviate all the above problems and provides a more attractive product for the farming community.
1.2 The Product
SMART-P™ granulated compound fertilisers are a range of nutrient balance OMF products specially designed to suit UK farming practices. Starting with the biosolids cake, the excess water is removed at 80°C in a tumbling evaporator to make the dry granules. The high temperature ensures that no harmful bacteria can survive the treatment, eliminating any re-growth risk. The dry granules provide the organic base for potash and urea deposition in a proprietary nutrient adjustment step. The overall process results in a free flowing, dust-free granular product with a narrow particle size distribution that can be bagged and applied using a standard fertiliser spreader.
Figure 1 (a) Schematic diagram of an OMF granule (b) Photo of an OMF sample.
SMART-P™ products are intended for surface dressings. Formulations OMF10 and OMF15 are ideally suited for grassland and wheat crop applications. The natural levels of P, S and micronutrients in the biosolids ensure an adequate supply of the vital elements for crop development with little risk of accumulation in the soil for regular product uses.
1.3 Agronomic and environmental performance
A comprehensive product trial programme has been undertaken by Cranfield University at Silsoe since 2007. Amongst the parameters investigated include the rate of nutrient release, crop yield response for grass and winter wheat as well as the fate of phosphorus. The results of the trials are summarised below.
Figure 2 (a) Lysimeters studies (b) Pot experiments (c) Plot trials
Figure 3 Grain yield vs. N application rate (2008 harvest)
Figure 4 Comparison of the environmental performance of different fertiliser options:
(a) Phosphorus accumulation. (b) Global warming potential (Salford University).
Farm scale demonstration of OMF application for various crops is currently on going on a commercial farm in the northwest of England.
Product Specification – Guaranteed Minimum Analysis of SMART-P™ products
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Organic base
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OMF10
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OMF15
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Solid content (%w/w)
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90%
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>85%
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>85%
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Particle size (mm, 95% confidence)
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3-6
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3-6
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3-6
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Organic content (% w/w)
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50%
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45%
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40%
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Total nitrogen (kg/t)
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35
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98.75
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139.54
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Soluble nitrogen (kg/t)
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1
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55
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105
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Total phosphorus (kg P2O5/t)
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55.73
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42.87
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37.39
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Potassium (kg K2O/t)
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1.24
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37.88
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37.88
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Total sulphur, (kg SO3/t)
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20.5
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15.77
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13.63
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E. coli, MPN/g solid
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<10
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<10
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<10
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Salmonella (P/A in 2 g solid)
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ND
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ND
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ND
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ND = below detection limit
KEY FACTS:
SMART-P™ is a range of granulated compound fertilisers made from biosolids. The free flowing granular OMF products are intended for surface dressings using a standard fertiliser spreader. Trials by Cranfield University have demonstrated that crop yield responses of grass and wheat for SMART-P™ were on a par with mineral fertilisers. No soil accumulations of phosphorus were observed after two years of application. Life Cycle Analysis suggests that the use of OMF in agriculture would result in a net reduction in greenhouse gas emissions.
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Organo Mineral Fertilisers
