Making the most of finite resources

Over the last few years, issues around sustainability have been high on the agenda. Whether in terms of energy use, both from a cost and a climate change perspective, the avoidance of waste and the protection of the environment have all become much more important considerations when making any management decision.

However, while access to water and soil are also recognised issues, the availability of other finite resources, such as nutrients, and other materials has not received quite as much attention. This is beginning to change. In the wider world businesses are starting to think about the so-called ‘circular economy’, as promoted by the Ellen MacArthur Foundation. According to their website, ‘A circular economy is one that is restorative and regenerative by design, and which aims to keep products, components and materials at their highest utility and value at all times, distinguishing between technical and biological cycles.’ The foundation also points out that today’s linear ‘take, make, dispose’ economic model relies on large quantities of cheap, easily accessible materials and energy, and is a model that is reaching its physical limits.

There are sound economic reasons for agriculture and horticulture to address the availability of certain resources. Global phosphate and potash are limited, and while figures produced by the United States Geological Survey (USGS) in 2012 suggested more than 350 years supply of rock phosphate, there are many uncertainties surrounding the figure. A similar calculation for potash suggests around 250 years of reserves. However, neither estimate considers the fact that the UN FAO estimates global demand is currently growing by around two per cent a year.

“The efficient use of resources and inputs will help producers to manage costs of production and improve profitability,” points out Leslie Berger, Agri-Food Sustainability Consultant at RSK ADAS UK Ltd. “Climate related limitations on water and potential increases in the cost and availability of water are driving improved efficiency of water use, while reducing water use and greenhouse gas (GHG) emissions is increasingly required by supply chain partners and customers such as processors, food service suppliers and retailers.”

Resource use calculator

In 2013 ADAS led a two year consortium project for the Agriculture and Horticulture Development Board (AHDB) to research and develop a Farm Scale Resource Use Efficiency Calculator. The main aim was to understand the environmental and economic impact of farm management decisions relating to resource use.

The resulting AHDB Environmental and Agricultural Resource Efficiency Tool (EAgRET) is available to levy payers via AHDB, but other tools are available to measure and monitor carbon emissions, including the Cool Farm Tool developed by the Cool Farm Alliance ( For those simply looking for introductory information, there are numerous sources, such as Defra’s Waste Minimisation Manual which can be found at

“The EAgRET project was developed in order to provide a tool to quantify the efficiency of resource use at a farm level, including where that farm has multiple enterprises,” explains Haroon Jabar of AHDB Horticulture. “The tool is unique in addressing the impact of transferring resources between enterprises and the impact that has on a range of environmental metrics. EAgRET is not designed to provide a decision making tool for individual farmers or growers, but rather to test scenarios for ‘typical’ farms in order to inform discussions with policy makers and evaluate research and knowledge exchange priorities.”

He adds; “improved resource efficiency can improve financial performance, for example by reducing the cost of inputs, at the same time as reducing the environmental impact of production. The tool enables scenarios to be tested so that trade-offs between different environmental metrics can be considered. However, improvements in resource use efficiency typically require a significant investment of time; to measure, plan changes, adapt or mitigate and then subsequently manage. In addition to time, there can also be significant financial investments to be made, although the return on investment can be relatively quick.”

Recycling veg waste

“Recovering and recycling vegetable waste can provide new income streams such as animal feed, anaerobic production or composting to produce energy and organic fertiliser,” points out Leslie Berger. “We are aware of a number of the larger vegetable growers who have invested in AD and are now using the energy produced and recycling the digestate back onto their crops.”

However, she points out that while organic materials such as digestate and composts contain valuable organic matter and plant nutrients, it is important that recycling of these materials to land is done carefully to avoid any risks to the food chain: “The main concern is potential pathogen transfer where growing fresh produce, but digestate and compost are generally very low in pathogens anyway as the treatment process kills pathogens. Any risk from purchased digestate can be further minimised by using a quality product, such as PAS 100 certified compost or PAS110 certified digestate, and following guidelines in Farm Assurance schemes such as Red Tractor, which sets out safe harvest intervals when applying wastes to fresh produce crops.” Growers should also refer to the Safe Sludge Matrix and the Renewable Fertiliser Matrix, both of which provide excellent guidelines.

Matt Hindle, Head of Policy for the Anaerobic Digestion & Bioresources Association (ADBA) points out that farming has been at the heart of the recent expansion of anaerobic digestion. “The AD market has grown very strongly in the UK over the last few years and the farming sector in general has been a very big part of that,” he says. “There are now around 540 anaerobic digestion plants in total, of which well over two hundred are on farms. They use a huge range of different feedstock materials, but the residue from vegetable processing can be a really important feedstock.”

As well as recycling nutrients, farmers benefit from a waste processing process which is often lower cost than the available alternatives, and energy generation. “The advantage of AD is that the nutrients recovered match the crop or vegetable waste that is put into the plant,” explains Matt.

“The biofertiliser that is produced, the digestate from AD, is particularly rich in nitrogen, phosphorus and potassium which are all crucial to plant growth, and the availability of the nitrogen is increased by the AD process, so you get more available nitrogen than from spreading the organic materials directly and the next crop can take that nutrition up very quickly. It is also a low carbon fertiliser, so your end product has a lower carbon footprint associated with it.”

Nutrient recovery

However, a lot of nutrients are lost through other non-farming activities and while the use of biosolids and sewage sludge is an established method of recovering resources, they are not always suitable for all crops or production systems, as well as needing specialist equipment and being subject to additional regulations. Because of this, entrepreneurs are now looking at recovering resources from materials like sewage and making them available to end uses such as farmers and other industries.

“The Pearl® process is a unique phosphate recovery system from both cleaning P and N from waste water and also providing a concentrated N-P-Mg complex fertilizer which vegetable growers may use,” explains Jim Welson, a Consultant with Ostara. “Some nutrients like phosphate are known to be a relatively limited resource, and in addition while all nutrients are needed to grow vegetables, some major ones like phosphate are utilized very inefficiently by crops, so the aim is to improve upon that uptake.”

Ostara Nutrient Recovery Technologies Inc. sustainably produces Crystal Green®, an enhanced efficiency continuous release phosphate fertilizer that has a guaranteed analysis of 5-28-0-16.7MgO. According to Jim, Ostara’s Pearl® process produces three mean granule grades, 1mm, 1.5mm and 3mm which are citric soluble and release the nutrients evenly over a period of 5 – 8 months.

“The product is clean and dry, not hygroscopic, and contains very low heavy metals relative to standard phosphates. It also has a low salt index and so may safely be placed in the rooting zone,” he explains. “It is not locked up and is available from very low to very high pH levels. The product is solid, is most efficient when placed in the root zone and used in conjunction with some water-soluble phosphate, although it has not yet been given clearance for use on organic crops.”

Unlike sewage sludge and digestate, and other forms of struvite, Crystal Green® is classed as an EU and UK fertilizer and not a waste and has a guaranteed plant available nutrient analysis. It doesn’t have the societal or environmental concerns associated with biosolids and digestate and has no restrictions as to what crop it can be used.

As demand for resources of all kinds continues to increase and society moves towards a circular economy, more companies such as Ostara are likely to appear, helping the agricultural and horticultural sectors play their full part. However, true sustainability means that this has to be done in a way which is profitable and provides the business itself with a future: “Growers have to continually challenge normal procedures, inputs and timings, but they have to do it in a way which provides them with sufficient empirical evidence to warrant the change,” Jim concludes.

by Richard Crowhurst.