## 2 Materials and Methods  
### Plant Material and Growth Conditions  
The experiment was carried out in accordance with the integrated production guidelines [9] at the experimental station of the Agricultural Institute of Slovenia, located in Brdo pri Lukovici (latitude, 46\({}^{\circ}\)10' N; longitude, 14\({}^{\circ}\)41' E). Each individual treatment (6 treatments) was repeated in five blocks (one plot for each treatment within one block), with 10 plants included in each plot. The field trial was carried out on silly loam soil rich in potassium and nitrogen and low in phosphorus, equipped with a drip irrigation system. Soil texture is silty loam with pH value of 6.1 and mineral composition of 9.5 mg/100 g P\({}_{2}\)O\({}_{5}\), 27 mg K\({}_{2}\)O/100 g and C organic matter stock (2017 soil analysis). Frigo strawberry cv. 'Clery' plants (_Fragaria \(\times\) ananassa_ Duch.) were planted in an open field on 7 August 2017 and covered with a non-heated plastic green-house in spring 2018. Slightly raised beds were covered with black polyethylene. Plants were planted in double rows, with 0.25 m \(\times\) 0.25 m spacing between the plants and 1.3 m spacing between the rows. Average day and night temperatures in the tunnel ranged between 10.5 \({}^{\circ}\)C and 24.3 \({}^{\circ}\)C during the production period. Light levels (0-757.3 W/m\({}^{2}\)) and humidity (53.2-99.4%) were under ambient spring conditions. An experiment was conducted to evaluate the application of different doses of nitrogen and calcium on yield and selected strawberry aroma compounds. Recommended dose of nitrogen (RDN) is 60 kg N/ha per year [9]. Six treatments were specified: CON (control)-without fertilisation, 33% of RDN (20 kg N/ha), 66% of RDN (40 kg N/ha), 100% RDN (60 kg N/ha), calcium chelate (CA-CH 1 g/L water) and Lithovit (LITH-5 g/L water). For nitrogen fertilisation we used urea, which consists of 46% N. For Ca fertilisation we used nano fertiliser Lithovit forte(r) (contains 80% calcium carbonate, 4.6% magnesium carbonate, 0.75% Fe) and calcium chelate with 10% Ca. We applied N using drip irrigation and Ca with spraying. The control plants were sprayed with water to unity the spraying with Ca spraying and irrigated with drips using only water. Fertilisation of the plants was performed during the furctification of strawberries weekly from 13 April 2018 (phenological development stages of strawberry [26]--first flower open (BBCH 60) until 15 May 2018 (beginning of harvesting--BBCH 87) early in the morning. For the nitrogen fertilisation treatments, we used 0.172% solution in divided doses, depending on the treatment required to reach the necessary concentrations, to avoid harming the plants due to high concentration. For the foliar application of calcium, the plants were sprayed in the morning, as the leaf stomata are open, and the effectiveness of the product is maximized. Foliar calcium application was performed on 3 April at full bloom (BBCH 65) and on 14 May, when the first fruits were harvested (BBCH 87). Each plant was sprayed until the leaves were completely soaked. Each treatment was repeated for five blocks and each block contained 10 plants. The number of fruits per plant and the total yield per plant were recorded on each harvesting date (from the beginning of harvesting and until the last fruits were harvested--BBCH 87-90): 14, 16, 18, 22, 24, 28, and 31 May, and 4, 7, and 11 June. Only ripe fruits were collected at each sampling date and the corresponding ripeness was determined according to the visual characteristics of the strawberries. Fruit samples for biochemical analysis (sugars, organic acids, phenolics, and volatile compounds) were collected at the third harvest on 18 May. The fruit was picked early in the morning when temperatures did not exceed 15 \({}^{\circ}\)C, labelled, immediately shock frozen in liquid nitrogen, stored in plastic bags, taken to the laboratory in liquid nitrogen and stored at \(-80\)\({}^{\circ}\)C for up to a week before further analysis was performed.