A new growing system for tomatoes
By Jørn Nygaard Sørensen, senior scientist, Danish Institute of Agricultural Sciences
The nutrient requirement for tomatoes is very high. In organic production, incorporating around 20 kg of stable manure per m2 fulfils this high requirement. Application of such high amount of manure may, however, increase the risk of nutrient losses for example by leaching.
When grown in soil, the plant roots may be injured by soil borne pests or diseases. In field grown crops these problems can be avoided by crop rotation. However, this possibility cannot be used in glasshouses.
Problems with soil borne pest and diseases and risk of losses of N and other plant nutrients have increased an interest in growing tomatoes in confined beds without soil contact. By growing in confined beds, leaching can be avoided by recycling drainage water, and problems with soil borne pest and diseases can be dealt with by replacement of growing medium. This medium can be reused as a soil conditioner for field grown crops.
However, organic growers believe that crops need to be grown in soil to ensure better supply of water and nutrients including trace elements. Therefore, it was the purpose to develop a new growing system, which benefits from the advantages of both soil growing and growing in confined beds.
In 2002, such a combined growing system was established with compost in boxes, which had holes in the vertical walls. Through these holes, plant roots grew into the soil surrounding the boxes. We compared this growing system with both common soil growing and growing in confined beds without soil contact. The compost was mainly made of organic clover grass and wheat straw and was used both as growing medium and nutrient source.
In such combined growing system, plants can take up water and nutrients from soil as well as compost, and drainage water can be recycled. Further, the compost can be replaced before each new planting. By using organic plant material for the compost, the grower is independent of the access to organic manure, which may be limited in some areas. In the combined growing system, plant roots may be injured by soil borne pest or diseases. However, we believe such problems will be less significant compared with common soil growing.
The total nitrogen content in the compost applied to the three growing systems was 95 g per m2. After seven month of growth we attained a yield of 35 kg per m2 in the combined system, 34 kg per m2 from soil-grown plants, and 32 kg per m2 from plants in confined beds. In the latter treatment, some early fruits developed blossom end rot, due to high cation activity ratios in the root zone. After four month of growth 55 g total N per m2 in legume plant material was applied. This supplemental application increased the yield by only 1 kg per m2 in all growing systems. The yields obtained were of the same size as at commercial growers.
During the growing period, the plants accumulated around 65 g N per m2. This N uptake originated from the applied compost and from soil mineral nitrogen. The highest yield was obtained by application of supplemental legume plants. Only in the combined growing system the soil mineral nitrogen was acceptable low at final harvest. By soil growing, the content of soil mineral nitrogen was still high with risk of losses by leaching.
|
