Productivity of lettuce fertilized with volcanic by-products of aggregate extraction

Abstract

This paper presents a study at field level on the effect of fertilization with two types of volcanic materials in organic horticulture production in the Mediterranean climate. Specifically, lettuce of the “maravilla” (summercrisp) type were cultivated in soil amended with basalt or volcanic sand, both by-products of aggregate extraction. The survey was performed at a biological farm with sandy loam soil in Bigues i Riells (Barcelona Prov., Spain).Different doses of volcanic mineral (0 t/ha, 9.8 t/ha, 13.1 t/ha, 16.38 t/ha and, in basalt, also 23.9 t/ha) and the same amount of compost (30 t/ha) made of manure and shredded plants on-site at the farm, were applied to 5 m2 plots. The plantation frames measured 30 cm x 30 cm and the lettuces were planted in between. Plots with different kinds of minerals were separated 50 cm from each other and drip irrigation was used. The study lasted 36 days and lettuce height and biomass production were measured (weekly and at the end, respectively) in order to assess the effects of the experiment. Finally, the results indicated that all the lettuces fertilized with volcanic material showed a greater height and biomass production than the controls (0 t/ha). In fact, the lettuces presented an average height increase of 3.3 % with volcanic sand and 4.4 % with basalt, and an average increase of biomass production of 16.5 % with volcanic sand and 15.9 % with basalt. On the other hand, an economic analysis seems to show that application of volcanic materials is especially profitable for doses of around 10 t/ha.

Keywords: fertilization, volcanic rock, biological production, lettuce.