Organic farming benefits the aquatic environment

By Uffe Jørgensen, Danish Institute for Agricultural Sciences (DIAS) & Erik Steen Kristensen, Danish Research Centre for Organic Farming (DARCOF)

Nitrogen is a crucial plant nutrient but can cause large problems in excessive doses. In the 1970s and 80s the water quality in rivers and lakes started deteriorating. The reason was extreme algal growth leading to oxygen depletion, with a drastic negative impact on plant and animal life.

The cause of algal growth was the supply of nutrients – in particular nitrogen and phosphorus – from agriculture and waste-water. The increased use of mineral fertilizer and intensification of animal production, in particular, caused a reduction in the utilization of nutrients and thus led to leaching of nutrients to other recipients such as the aquatic environment.

In order to limit the discharge of nutrients, the Danish parliament in 1987 passed a national Action Plan on the Aquatic Environment (VMP I) with the ambitious aim of reducing the discharge of nitrogen by 50% by year 2000. In agriculture, the main reduction in nitrogen leaching was to come from an increased use of winter crops, an improved utilization of animal manure and a reduction in the use of mineral fertilizer.

It became clear, however, that further measures would be needed if leaching were to be sufficiently reduced. In 1998, a further Action Plan was therefore enacted (VMP II), which tightened the regulations on fertilizer use and included further measures on changes in land use (e.g. afforestation and organic farming).

Evaluation of VMP II

VMP II has recently been evaluated by scientists from the Danish Institute of Agricultural Sciences (DIAS) and the National Environmental Research Institute (NERI). According to the evaluation, the leaching of nitrogen (N) from Danish agricultural soils has been reduced from about 311,000 tonnes N per year in the mid 1980s to about 168,000 tonnes N per year in 2002.

A prognosis was prepared in connection with the evaluation showing a further reduction in the level of leaching of 6,000 tonnes N per year when VMP II is fully implemented at the end of 2003. Leaching of N is then expected to be 162,000 tonnes per year. On this basis, NERI and DIAS concluded that the objectives of the two water actions plans have largely been achieved.

The Water Action Plan uses two different avenues of implementation. One avenue encompasses measures relating to fertilizer use, the other avenue measures relating to land use. The fertilizer-related measures are the regulations set by the action plans in terms of the balance between farm acreage and the number of animals allowed, the use of catch crops, reduced fertilizer standards and stricter regulations on the use of animal manure (improved utilization of nutrients in animal feed numbers as one of the options). The land-use-related measures include conversion of conventionally farmed areas to wetlands, forests and environ-mentally sensitive areas (ESAs), and conversion to organic farming.

Table 1 shows the effects of the individual measures. Organic farming emerges as by far the most effective land-use-related measure in the Action Plan. The area converted is not as large as that budgeted in VMP II, but the reduction in N leaching per ha, particularly in organic livestock farming, has exceeded the expecta-tions of VMP II.

Organic farming in VMP II

The expectation at the mid-term evaluation of VMP II (year 2000) was that c. 156,000 ha could be con-verted to organic farming during 1998-2003. According to the Danish Plant Directorate, the area under organic farming was 64,329 ha in 1997 and 178,360 ha in 2002. For 2003, the area is actually expected to decrease, so that by the end of 2003 the area will be c. 175,800 ha. At the full implementation of VMP II, the organically farmed area is expected to have increased by 111,500 ha – or c. 44,500 ha less than originally envisaged.

However, conversion has had a greater effect than budgeted. The mid-term evaluation of VMP II thus assumed that a conversion to organic farming would reduce N leaching by 10 kg N per ha. On the basis of analyses in DIAS/DARCOF, however, it is now estimated that conversion during the VMP II period reduced N leaching by an average of 33 kg N per ha compared with the average level of leaching from conventionally farmed areas in 1998.

It is in particular the conversion to organic livestock farming that has had a greater effect than previously assumed. It is estimated that conversion to organic farming until 2002 has resulted in a reduction in N leaching of c. 3,700 tonnes N per year, where the calculation only includes the fully converted area. The prognosis at the end of 2003 shows a total reduction in leaching of c. 3,700 tonnes N per year where the total area is included, i.e. both the fully converted area and the area under conversion.

Organic farming in VMP III

Organic farming is also one of the possible elements in the third Action Plan for the Aquatic Environment, which has to be negotiated during this winter. The evaluation of the effect of conversion of dairy farming is based on a new analysis of farm balances, which shows that a conversion from conventional to organic dairy farming results in a reduction of N leaching by 46-50 kg N per ha per year.

Conversely, a simulation of leaching from conventional and organic arable farming with the FASSET model (November 2003) shows increased leaching levels when converting to an organic production. The increase amounts to 5-10 kg N per ha. These calculations are based on conventional arable farming prac-tices without specialty crops, but with a large proportion of cereal in the rotation. The organic arable farmers are, however, a very diverse group. The group is characterised by having a small number of animals while importing relative large amounts of animal manure (compared with conventional farming). This dif-ference contributes to the larger level of N leaching from organic arable farming. The calculations also show, however, that an improved effect of organic arable farming can be achieved through changes in the crop rotations and through an increased use of catch crops.

Dairy and arable productions constitute by far the largest sectors in organic farming. Assuming conver-sions from these two sectors are similar in size, the expected effect of the conversion would be an average of 20 kg N per ha. This figure will change with different rates of conversion for the two sectors.

Reference

Ib Sillebak Kristensen, Niels Halberg, Anders Højlund Nielsen, Randi Dalgaard and Nich Hutchings, (2003). N turnover on Danish mixed dairy farms. Paper presented at workshop “Nutrient management on farm scale: how to attain European and national policy objectives in regions with intensive dairy farming?” 23-25 June 2003, Quimper, France. (pdf)