New organic growing system reduces losses of nutrients
By Jørn Nygaard Sørensen and Kristian Thorup-Kristensen, Danish Institute of Agricultural Sciences
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Producers of organically grown greenhouse tomatoes grow their plants in soil where plant roots are not restricted in nutrient uptake. In this system a risk of nutrient leaching arises due to application of organic farm manure and surplus irrigation. |
The leaching risk is avoided when plants are grown in confined beds, but it has been questioned whether such cropping is in agreement with the principles of organic production. Therefore, there may be a need to develop a growing system, which combines the advantages from both the soil grown and confined systems.
We have developed a combined system using compost-filled containers with holes in the vertical sidewalls, which enables the roots to grow out into the soil (Figure 1). The drainage water was re-circulated. At the end of the growing period, the compost can be re-used as soil amendments for field-grown crops.
High yields with compost in the new growing system
In confined beds and in the combined system, plants were grown in a six-week compost of chopped hay of clover grass, deep litter and peat. Equal amounts of compost mixed into the soil were applied to plants grown in open beds.
On average of two experiments, the cumulated production in October after seven month of growth was (Figure 2):
- 39 kg per m2 in combined beds
- 37 kg per m2 in open beds
- 32 kg per m2 in confined beds.
Application of supplemental fertilizer did not increase fruit production considerably.
The plant available content of soil N to 1 m soil depth in February-March before planting was 64 and 25 g N per m2 in 2002 and 2003, respectively. In these two years, 117 and 196 g N per m2 was applied with the compost. Having in mind that the compost in October was not fully decomposed, this N supply was sufficient to create an acceptable yield.
Reduced risk of leaching
In October at the end of the production period, the soil N content in the top 1 m soil layer of combined beds without supplemental fertilizer was equal to or halved compared to open beds without re-circulation of drainage water (in 2002 and 2003, respectively, see Table 1).
Application of supplemental fertilizer did not increase the soil N content in combined beds. In contrast, the soil N content in open beds was considerably higher when supplemental fertilizer was applied. Here, an increased risk of N losses occurs if the succeeding crop is applied surplus irrigation water.
Conclusions on the new growing system
- It is possible to grow greenhouse tomatoes and achieve high yields by application of compost of clover grass, deep litter and peat.
- It is possible to re-circulate surplus irrigation water and at the end of the growing period to re-use the compost as soil amendments for field-grown crops.
- Use of new compost at plant establishment of each new crop may reduce problems with soil-borne diseases.
- The risk of N losses through leaching is reduced.
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