Effect of flat covers on macronutrient concentrations in arugula leaves

Arugula is a common name for several leafy vegetable species of the family Brassicaceae, characterized by a strong aroma and pungent peppery flavor. The perennial wall rocket Diplotaxis tenuifolia (L.) D.C. and the annual salad rocket Eruca sativa Mill. are grown commercially for human consumption. The objective of this study was to determine the effect of two types of flat covers, perforated PE film and non-woven PP fabric, on macroelement concentrations in arugula leaves. A two-factorial experiment was conducted in 2006 - 2008 in the Experimental Garden of the University of Warmia and Mazury in Olsztyn. The experimental factors were: (1) plant species Diplotaxis tenuifolia (L.) D.C. and Eruca sativa Mill., (2) the type of plant cover perforated PE film with 100 openings per m 2 and non-woven PP fabric with surface density of 17 g m -2 ; plants grown without protective covers served as control. Arugula was grown on proper black earth soil of quality class IIIb and cereal-fodder strong complex. Each year, seeds were sown in the middle of April. After planting out in the field, the seedlings were covered with PE film or non-woven PP fabric. The covers were removed after approximately five weeks. Leaves were harvested gradually over the growing season, one to three times from each treatment. The concentrations of mineral compounds were determined in dried plant material from the first harvest, as follows: total nitrogen – by the Kjeldahl method, phosphorus – by the vanadium molybdate method, potassium and calcium – by emission flame photometry (EFP), magnesium – by atomic absorption spectrometry (AAS). The concentrations of all analyzed macroelements in arugula leaves were significantly affected by both plant species and the type of cover. Leaves of Diplotaxis tenuifolia (L.) D.C. had a higher content of phosphorus, potassium and calcium, whereas leaves of Eruca sativa Mill. accumulated more total nitrogen and magnesium. Leaves of arugula plants covered with non-woven PP fabric contained the highest concentrations of phosphorus, potassium, calcium and magnesium, while plants covered with PE film had the highest total nitrogen content. The Ca:P, Ca:Mg and K:Mg ratios were wide in all treatments. The K:(Ca+Mg) and K:Ca ratios were relatively narrow, but they remained within the normal range.