Archived at http://orgprints.org/4644 

Optimising nutrition in organic tomato production
Dr. Kristian Thorup-Kristensen
Danish Institute of Agricultural Science

In our tomato project we have identified two main problems in organic tomato production which we wanted to address:
1.	Crop rotation is one of the main tools to handle crop nutrition, pests, and diseases in organic farming. This is not used in the greenhouses where the same crop will typically be grown year after year. This leads to problems with build up of soil borne pests and diseases as well as with nutrient balances and losses. To manage these problems we are working with tomatoes grown compost in containers.
2.	In organic tomato production large amounts of plant nutrients are needed. The supply of organic manures for organic farming is limited by many regulations which are likely to become even stricter in the future. Farmyard manure from farms with organic livestock production can be used with few regulations. However, the supply is dependent on livestock farms which have limited availability of plant nutrients themselves, and which may be located far away. To handle this problem we try to use easily available crop residues to supply most or all of the nutrients needed for the tomato crop. 

Open or closed containers for tomato production
As crop rotation is not realistic in greenhouses, we try to develop systems where the growing medium can be changed from year to year instead. This means that each tomato crop can be planted in a “fresh” growing medium. To do this, we grow tomatoes in compost in long containers with 12 plants in each. After each crop, the compost can be recycled to the field, while fresh compost is put into the containers for the next tomato crop. We work with two types of containers, one type where the tomato root system is confined within the container and another type where holes in the sides of the container walls allow roots to develop also in the soil outside the container. 
The idea behind this “intermediate” where tomatoes are grown in containers, but also have access to the soil outside the container is to try to combine the advantages of the two alternative systems where tomatoes are grown either directly in the soil or confined within the containers. Allowing the root systems to spread in a large soil volume offers clear advantages in terms of water and nutrient supply. Further, it has been questioned whether growing crops without access to the soil can be accepted in organic farming. 

Soil grown

Intermediate system
 - containers allowing root growth in soil outside the container

Closed 
containers

Results of two years of experiments have shown that tomatoes can be grown successfully in containers, but that the intermediate system gave the best results with higher yields than the soil grown tomatoes. Tomatoes with their roots confined within the containers gave a lower yield and showed some problems with blossom end rot. Though successful systems where the tomato roots are confined within the compost can probably be developed, it is questionable whether this is worth doing considering the very promising results obtained with the intermediate system. Thorough studies of tomato quality did not show any significant effects of growing system. 

Crop residues as “manure” for tomatoes
If the nutrient supply for organic tomato production can be based on crop residues, the “manure” can be produced locally, either by the tomato producers or by contract with local organic farmers. Plant materials, especially legumes, can be efficient sources of nutrients for crop growth. We have used clover-grass hay, lucerne pellets and wheat straw to supply most of the nutrients for the tomatoes grown in our experiments, and have obtained high yields. We have also worked on producing composts based solely on crop residues. This also looks promising, though we have not tested composts based only on crop residues for tomato production yet. 
Important aspects to consider is compost structure and aeration, drainage, irrigation systems which keep all of the compost moist, and nutrient balances, but this is true with composts based on farmyard manure or other sources of organic matter as well.