Großaufnahme eines Traktors, der auf einem Feld Gülle ausfährtClick to enlarge
With the manure go too many nutrients in the soil and charge such as groundwater.
Source: Hans von der Beele / Thinkstock

What exactly is fertilizer?

In order to develop and grow, apart from adequate water, plants need nutrients such as nitrogen, phosphate and potassium and trace elements such as copper and zinc. Only if these requirements are met can high yield, high quality crops be obtained. Crop plants obtain nutrients and trace elements from the soil via their root systems, a process in which soil humus content plays an instrumental role. Humus is rich in plant nutrients and has very high water retention capacity. The long term crop yield potential and fertility of soil can only be assured if the soil retains the nutrients that are removed when crops are harvested. Hence using fertilizer containing the exact nutrients needed by the crops being grown in the soil is indispensable. A distinction is made between mineral fertilizers and organic fertilizers, whereby the latter comprise livestock manure, vegetable manure, mulch, organic-residue fertilizer, and growing media such as composted biowaste, sewage sludge, and growing media (horticultural peat). Mineral fertilizers are synthetically manufactured fertilizers containing one or more nutrients.

Environmental impact

Improper fertilizer storage and handling can provoke a host of serious environmental hazards. Moreover, mineral-fertilizer manufacturing is highly energy intensive, resulting in greenhouse gas emissions and extensive resource use. Nitrogen and phosphorous have a particularly devastating effect on soil fertility and waterbody quality. Air quality can be negatively affected by the ammonia emissions resulting from manure storage and use, as well as by nitrous oxide emissions from ground on which manure has been spread.

Heavy metals in fertilizer

Apart from beneficial trace elements such as copper, zinc and iron, fertilizer also contains heavy metals that crop plants do not need, including lead, cadmium, nickel, mercury, arsenic and uranium. Intensive fertilization can result in these elements accumulating in the soil and entering the food chain through crop plants and groundwater. One of the main culprits in this regard is phosphorous fertilizer derived from raw phosphate of sedimentary origin containing high concentrations of heavy metals, mainly cadmium and uranium.
Heavy metals are incorporated into sewage sludge in a variety of ways, including through water line corrosion, metalworking industry discharges, and pharmaceutical residues. Heavy metals (particularly zinc, copper and in the case of liquid pig manure, arsenic) can be incorporated into manure via substances such as livestock-feed additives. All heavy metals are toxic in high concentrations, although some heavy metals such as copper, iron and manganese are also essential trace elements and are necessary for key metabolic processes in plants, livestock and humans

The heavy metals that are relevant for human health are those that enter the food chain via absorption by crop plants and livestock. Länderarbeitsgemeinschaft Boden (LABO)’s Schwermetalltransfer Boden/Pflanze (heavy-metal transfer to plants and soil) working group reached the conclusion that arsenic, iron, cadmium, mercury and thallium are “predominantly relevant” for crop plant quality. The main heavy metals that can be incorporated into livestock food via forage are nickel and copper. Although they do not pose a risk to human health, they are toxic to certain soil microorganisms and can thus have a long term impact on soil fertility.

Fertilizer legislation

The manufacture, placing on the market and use of fertilizers, soil improvers, culture media and plant aids are governed by the Fertilizer Act (DüG) and its regulations. The Düngemittelverordnung (DüMV) (fertilizer regulation) lays down the requirements for placing fertilizers on the market. Compliance with these requirements is monitored by official fertilizer transport controls known as Düngemittelverkehrskontrolle (DVK). The Fertilizer Act (DüG) stipulates the following: (a) fertilizer is to be used solely in accordance with good agricultural practice; (b) fertilizers are to be compatible with the type, quantity and timeline related nutrition needs of the plants in question; and (c) fertilizer use is to take into account available soil nutrients, the organic substances in the soil, and local and cultivation related conditions. The Düngeverordnung (DüV) regulation fleshes out the usage criteria in accordance with good agricultural practice for fertilizer use. These criteria pertain to matters such as determining fertilizer needs, the timing of fertilizer application, buffer strips for surface waterbodies, and rules concerning ammonia emission abatement. The Düngeverordnung regulation also transposes Directive 91/676/EEC into German law.

The Verbringungsverordnung (marketing regulation) governs placing on the market, transport and taking possession of manure, as well as the related commercial substance streams.

In order to avoid soil contamination by heavy metals and endangering human health and the environment, it is essential that fertilizer use be monitored efficiently. Limits on heavy metal inputs in Germany are governed by the fertilizer regulations (DüMV) and waste management regulations (BioAbfV, AbfKlärV). In addition, the Bundes-Bodenschutz- und Altlastenverordnung (BBodSchV) (soil protection regulation) as well as the Law on Food and Feed (LFGB) lay down limit values for pollutants and heavy metals. However, there are in some cases substantial differences between the stipulations in these various laws, concerning matters such as the pollutants that are actually regulated, pollutant concentrations and loads, the applicable limit values, and the relative importance of the various protection objectives in terms of human and livestock health, the ecobalance and environmental media. There are also some discrepancies between German laws and the applicable EU laws.

In light of these inconsistencies, the Federal Ministry of Food, Agriculture and Consumer Protection (BMELV) asked its scientific advisory panel on fertilizer related matters to make recommendations as to how readily implementable laws that will be compatible with future EU laws on fertilizer pollutants can be implemented for Germany’s fertilizer laws. The panel’s recommendations, which were issued in 2011, provide a comprehensive approach to harmonized assessments of fertilizer pollutants and for placing limits on the pollutant inputs arising from fertilizer use. They can be downloaded from the BMELV website.

The panel’s recommendations do not, however, propose a limit value for uranium, a heavy metal that at present is insufficiently regulated by Germany’s environmental laws. Various studies have detected uranium from phosphate fertilizer in soil, leachate and groundwater.Over the past decade, an average of 167 tons of uranium from phosphate fertilizer has been deposited on crop fields. If this uranium ends up in groundwater, elevated drinking water purification costs over the long term could be the result.

Hence the UBA’s soil conservation panel has recommended that uranium content in phosphate fertilizers be regulated as follows (as is the case with cadmium): labelling for phosphate fertilizers containing 20 milligrams or more of uranium per kilogram of phosphate; and a limit value of 50 milligrams per kilogram of phosphate.