PREFACE

The final activity of the network was to organise this conference to both report on some of the activities of the ENVEG network, but also to gather together expertise on important aspects of N fertilisation of field vegetable crops. We hope that these proceedings have met those aims.

Synopsis of the Conference
The conference was held at the Steigenberger Hotel, Potsdam between the 30th August and 1st September 1999. The first two days were occupied at the hotel with the third day reserved for field visits. This conference was the culmination of three years work for the EU concerted action ENVEG, and was attended by 70 participants, representing 21 countries. The conference was jointly organised by Dr Clive Rahn of Horticulture Research International in the United Kingdom and Dr Matthias Fink of the Institute of Vegetable and Ornamental Crops Grossbeeren/Erfurt e.V. in Germany; and was opened by Dr Hardy Rabisch, a deputy of the agricultural minister of the local Brandenburg Land. The programme consisted of twenty-three oral presentations and twenty one posters grouped in four sections:
1) Current recommendations systems
2) Efficient fertiliser application
3) Sustainable management
4) Methodology: Tools for N research

The scientific programme was introduced by two invited speakers, providing background for the concerns about nitrates in the environment and in food. Dr. Jacques Neeteson spoke on ‘The effect of nitrogen on the environment in field vegetable cropping’, and Dr. Alphons Boink spoke on ‘The health effects of nitrates and nitrites’. Following papers then provided options to reduce such problems which included the use of fertiliser recommendation systems, employing different forms of N fertiliser, placement of fertiliser, the management of crop residues and choosing of crops to make best use of N. Some major gaps in knowledge were highlighted, such as our understanding of the cycling of N in soils following crop residue incorporation. In the final papers we heard about the tools available for carrying out N research for field vegetable crops such as use of computer simulation models, measurement of leaching, mineralisation of N and methods for measuring soil mineral nitrogen.

The Way Ahead
Jacques Neeteson outlined several potential environmental problems associated with growing field vegetable crops. One related to the amount of fertiliser applied; if in excess to crop demand, unused fertiliser can be left in the soil at harvest. Another related to how much of the crop is left in the field after harvest, for some crops, such as Brussels sprouts, over 70 % of the crop remains. This excess N if not managed correctly can lead to excessive nitrate levels in groundwater. Excess N can also lead to excessive levels of nitrate in the leaves of crops particularly spinach and lettuce. Alphons Boink told us that 15% of the adult population in the Netherlands received more than the Acceptable Daily Intake of nitrates in food and water. Though the ADI concept gives a very high degree of protection to the consumer against exposure to nitrates, prolonged exposure at this level was not recommended. Alphons quoted Paracelsus (1493-1541)

'All substances are poisons; there is none which is not a poison. The right dose differentiates a poison from a remedy'.

In order to protect the environment and our health, the EU have instituted directives to provide maximum levels of nitrate in drinking water and food. It is therefore our job to provide the horticultural industry and government policy makers with guidelines for sustainable production of field vegetable crops based on sound scientific principles. The guidelines also need to be sufficiently practical to be used at farm and field level. We need to be able to facilitate sustainable production of vegetables in terms whilst minimising environmental pollution.

In order to be able to achieve these aims we need to understand the processes occuring in the soil, the plant, and the interactions between them and the atmosphere. At the conference there were papers which collected together part of our current understanding. For example, we heard about estimating crop demand for nitrogen, estimating when that nitrogen is needed by the crop and how the structure of the crop rooting system could affect the recovery of that nitrogen. From a knowledge of the rooting system and N requirement, perhaps fertiliser can be placed rather than broadcasted. In thinking about the amount of fertiliser to apply we have to consider the supply from the soil. This can come from the breakdown of soil organic matter but also from the release of N from previous crop residues. We must be able to understand more fully the supply of N from the soil, for example how quickly it becomes available and where in relation to crop roots. These remain challenges to be solved by future research and will keep us busy.

Once the supply is understood we can make more accurate predictions of the nitrogen that we need from fertiliser to satisfy crop demands. We then have further questions to ensure that the nitrogen is applied using suitable techniques particularly in drier Mediterranean environments. Do we use liquid or solid fertilisers?, how do we schedule irrigation to maximise efficient use of nitrogen? Even if we solve the problems of matching supply and demand for nitrogen we still have to deal with crop residues, which in the case of Brussels sprouts leave over 250 kg/ha N and more if the whole crop is ploughed in. We need to know how to transfer that nitrogen into the next cash crop. Do we use a cover crop?, and if we do will it release the N in time for the next cash crop to benefit? In intensive vegetable cropping rotations we have to consider more than single seasons but whole crop rotations. Brussels sprouts may not be an environmentally risky crop if the rotation can be managed to ensure that residual nitrogen is used by the following crop.

The meeting demonstrated that we have to continue networking, we cannot all measure everything on all our experiments, we cannot all be experts on roots, or crop demand, gaseous losses etc. The funding for the EU ENVEG project finished in June 2000. I hope that the networking that ENVEG has initiated will continue.

Clive Rahn (ENVEG co-ordinator), June 2001

More information is available at www.hri.ac.uk/enveg/