DISTRIBUTION OF MACRONUTRIENTS IN ORGANICALLY GROWN JERUSALEM ARTICHOKE (HELIANTHUS TUBEROSUS L.) TUBERS THROUGHOUT THE GROWING PERIOD

The aim of this research was to evaluate the distribution of macronutrients in organically grown Jerusalem artichoke (Helianthus tuberosus L.) tubers throughout the plant growing season. During the years of 2012 - 2014, the following Jerusalem artichoke cultivars were grown for our investigations on an organic farm in the south of Lithuania: Sauliai, Albik and Rubik. The soil had the following agrochemical characteristics: soil pH(KCl) 6.7-7.5, available phosphorus 101-232 mg kg(-1), and available potassium 65-98 mg kg(-1). Additional fertilizing was applied to maintain such agrochemical characteristics during all research years. Samples were taken eight times during the growing season of tubers: in March-June (spring period) and August-November (autumn period). Dry matter (DM) content was determined by drying samples to the constant weight at the temperature of 105 degrees C; N - by Kjeldahl method; P - photometrically after wet digestion in sulphuric acid; K, Mg - by atomic absorption spectrmetry (using an Analyst 200). The data were statistically treated using ANOVA data analysis and the management module of the integrated system Statistica. For the evaluation of the analytical results, one-factor analysis of variance was carried out. Averages of separate treatments were calculated, the standard deviation and the least significant difference at a 95% probability level were estimated using the Fisher's LSD test (P < 0.05). The distribution of macronutrients in organic Jerusalem artichoke tubers throughout the plant growing period is largely associated with their organogenesis stage. The highest dry matter and nitrogen content were established in tubers of the cultivars Sauliai and Albik in March, while the highest content of potassium and magnesium was determined in tubers of the cultivars Rubik and Sauliai in May. The highest phosphorus content was in the tubers of cv. Rubik in November.