The future of fertilisers

Fertilisers and Turf

For intensively managed turf, fertiliser input is essential to promote growth and to allow grass to recover from wear and tear. By far and away the most important nutrient for grass growth is nitrogen.

A considerable amount of research has been carried out to ascertain the total amounts of nitrogen (N) required for golf greens and football/rugby turf, growing under a range of conditions from sand-based constructions to normal soils.

Other nutrients are important, e.g. phosphate and potassium. The former is particularly important for seed establishment, the latter for drought tolerance and strength of growth. Deficiency in these may occur in some soils, and this can be ascertained by soil testing. Other nutrients, such as sulphur, magnesium and calcium, are not likely to be deficient in most soils. In addition, there are micronutrients, such as copper and manganese, which are required by the turf in very small quantities and are rarely found to be deficient.

The Environment

There has been increasing concern about the environmental impacts of using fertilisers and, in particular, nitrogen. Up until now, this has focused on the potential for N to be leached as nitrate from soils to adjacent waterways or to aquifers used for drinking water. As a consequence, some precautions are taken in turf management, e.g. the use of controlled release fertilisers in situations where leaching could be a problem, for example where there is poor grass cover (it is worth noting that a dense turf is actually very efficient at taking up any applied fertiliser). The optimum amounts of fertiliser application for turf growth are not likely to lead to any major leaching of N.

Phosphate application on golf greens is generally kept to a minimum and unlikely to lead to leaching losses. However, greater amounts tend to be used on winter games turf and so losses are potentially greater, especially on sand-based constructions. However, it should be noted that phosphates do tend to be immobilised in soils, thus reducing losses in drainage water.

Large amounts of potassium are commonly applied in turf maintenance, probably much more than are actually needed. For sand-based rootzones the amounts leached are likely to be substantial.

Energy and Resources

Although the concern about over-application of these nutrients has been associated with ecological aspects (particularly with nitrogen and phosphate), the concern is now widening to take in other environmental and economic aspects. The first of these is the high energy requirements required to produce fertilisers, especially nitrogen. This is of particular concern for nitrogen, because the process of producing ammonium from atmospheric nitrogen has an extremely high energy input, with associated carbon dioxide output if fossil fuels are being used to produce the energy. The energy requirement is known as the embedded energy of the nitrogen.

Phosphate and potassium also contain embedded energy for their production as fertiliser. The table shows the calculated amounts.

Therefore, for a one hectare area (10,000 m2) of intensively managed turf receiving 25g/m2 of N from ammonium, the energy input is 5.2Wh x 25 x 10,000 = 1,300kWh of energy.

This is the energy content of 135 litres of petrol.

A second area of concern is that some of the minerals mined and quarried for producing the nutrients in fertiliser are running out. This is particularly true for phosphate, where the rock phosphate in Morocco and other countries is becoming depleted; and therefore more expensive. There are resources in China, but very little is being exported. This phosphate is required for agricultural production and, indeed, there are major concerns that production could be limited through the lack of phosphate. It is an extremely serious issue.

Recycled products

Scientists and other practitioners have realised that the situation with regard to fertiliser for food crops needs to be addressed. A major focus of current research is the capturing of fertiliser nutrients in waste materials and re-using them as fertiliser. There is a considerable amount of work being carried out on this at present. For instance:

- Composted green and food waste contains N, P and K which can be re-applied. However, the concentrations tend to be rather small, and substantial quantities of compost would need to be applied to intensively managed turf

- Waste water in water treatment centres contains significant quantities of nutrient, particularly phosphate derived from many domestic products. Industrial processes are now being installed to capture the phosphate, along with nitrogen, and process it to a fertiliser

- There is an increasing processing of food waste in the UK through anaerobic digestion. This is a biological process whereby methane gas is produced from the food waste material and, thereafter, used for energy production. However, most of the food waste is still present and requires disposal. It is normally split into a liquid and solid fraction. The liquid fraction contains some N, P and K, along with other nutrients such as sulphur, and it can be used as a fertiliser, although nutrient levels are low. The solid fraction can be composted

- By-products from industrial processes may produce nutrients. In turf management, ammonium sulphate is commonly used as an N source and most of this is derived from an industrial by-product. There are likely to be other materials with fertiliser value

- Greater interest is being taken in the ability of some plants to 'fix' atmospheric nitrogen. Clover is used to fix atmospheric N and is used within some turfgrass mixes. The possibility also exists to process leguminous crops such as peas or beans to produce a nitrogen fertiliser. As nitrogen fertiliser prices continue to increase, this may become an economically sound strategy for producing fertiliser

Most of these technologies are at an early stage and further developments will take place over the next few decades. However, because of increasing energy prices, the technologies used must have a low energy input.

One way or another, the cost of fertiliser will continue to increase and more recycled material will be used as fertiliser.