Vallört som växtnäringskälla
växtnäringsförsök och litteraturstudie
Russian comfrey, Symphytum x uplandicum, was tested as a plant nutrient source in a trial with tomatoes. Comfrey liquid was produced by Stiftelsen Holma i Höör. Tomato plants of the cultivar Aromata planted in a medium of soil:peat (1:1) enriched with organic nutrients and lime, were fed with comfrey liquid plus Biofer, in three different concentrations. Two different concentrations of BioRika were used as comparison, along with an unfertilized control group. In the comfrey treatment I a total amont of 1g N, 0,23 g P, 0,84 g K, was given to the tomatoes. In comfrey treatment II they were given 1,3 g N, 0,3 g P, 1 g K, and in comfrey treatment III they were given 1,7 g N, 0,4 g P och 1,9 g K. In the two treatments with BioRika the tomatoes were given 0,23 g N, 0,08 g P, 0,3 g K and 0,44 g N, 0,15 g P, 0,6 g K, respectively. The treatments were given at 11 occasions, starting when the tomatoes were 34 days and ending when they were 64 days old. The treatments gave a significant effect on the fresh weight, water content/dry matter, pH and conductivity, as the unfertilized control group differed considerably from the fertilized groups. No significant differences between the comfrey treatments and the BioRika treatments appeared during the short experimental period.
A literature study was also made with the aim of reviewing earlier trials with comfrey as a plant nutritent source. Even though the use of comfrey is widely spread among organic growers in England and USA, there are very few scientific papers on the subject. In order to supplement the research history, other applications of comfrey are presented, and also other species which can be used as plant nutrition sources, perhaps in combination with comfrey.
The literature study shows that comfrey liquid is not sufficient as a total fertilizer. The low nitrogen content makes it less suitable for organic transplant production. However, comfrey liquid can be used in fruit setting crops as tomatoes, peppers and cucumber, from the time of flowering, as it is a rich source of potassium. Due to the content of pyrrolizidin alkaloids in comfrey it is desirable with more studies about the toxic substances, to see whether they are taken up by crops fed with comfrey.