Effect of Plant Preparations on Lettuce Yield

Plant preparations are commonly used in organic horticulture. Herbal teas and broths are considered to be plant growth stimulating and disease suppressive. However, scarce scientific support is available. The aims of this work were to evaluate the effect of onion (Allium cepa) and stinging nettle (Urtica dioica) preparations on the growth of lettuce crops. The experiments were carried out in the Experimental Organic Orchard of the Faculty of Agronomy, University of Buenos Aires. The assays were planned as completely randomized blocks, with 6 replications per treatment. Lettuce (Lactuca sativa 'Criolla') was sown in continuous rows (3 kg seeds/ha) in each 1 m(2) minimum tillage experimental unit. Manual thinning out was required to reach an optimum number of plants per area. Onion and nettle preparations were obtained as follows. Broths were prepared by boiling 1 kg of chopped bulbs or leaves, respectively, in 10 L of water during 20 min, fermenting during 15 days, filtering and adding water to complete 10 L. Teas were prepared by chopping 1 kg of bulbs or leaves, respectively, adding 10 L of water, fermenting during 15 days, filtering and adding water to complete 10 L. Each preparation (diluted 1:20) was applied to the corresponding experimental units 3 times per week, during the whole crop cycle. Controls were treated with water. Plots treated with onion tea showed the highest leaf area and fresh head weight. Variations in the analyzed chemical components of the different plant preparations can, at least, partially explain these results. Further research is needed on the presence and role of organic compounds present in these preparations.