Effect of nitrogen rate and water replacement level on leaf biomass production and leaf nitrogen concentration of ten pot-grown blueberry cultivars

Soilless blueberry ( Vaccinium corymbosum L.) production is an alternative system that is increasing worldwide in surface area. There is little scientific information available as yet on the agronomic management of this cultivation system. The objective of the present study was to evaluate four N rates (0%, 100%, 200%, and 300% of the reference rate) and three water replacement level (70%, 100%, 130%) on leaf biomass production and leaf N concentration previous to winter fall (May and August 2021) in 10 pot-grown blueberry cultivars (Blue Ribbon, Duke, Camelia, Cargo, Last Call, Legacy, Ochlockonee, Suzie Blue, Ventura, and Victoria). An experiment was conducted in south-central Chile (36°55’ S) with first-year plants. During the first growing season, results showed interactions between cultivars, N rates, and water replacement levels; there was a synergistic effect between N rates and water replacement levels on leaf biomass production in ‘Duke’, ‘Camelia’, ‘Ochlockonee’ and ‘Suzie Blue’. Overall, the highest leaf biomass production in most cultivars was obtained with an N rate ranging from 33.2 to 53.1 g plant -1 season -1 (100% and 200% N rates, respectively) and 100% and 130% water replacement levels. Water consumption during the season fluctuated between 93.79 a 136.23 L season -1 . The highest leaf N concentration in most of the blueberry cultivars was obtained with N rates ranging from 33.2 to 53.1 g plant -1 season -1 and 70% and 100% water replacement levels. Therefore, agronomic management recommendations for N fertilization and water replacement levels in blueberries produced with this growing system cannot be generalized. One-year-old blueberry plants were placed in 35 L pots filled with a 2:2:1 (v/v) mixture consisting of coconut fiber, peat, and perlite with a density of 20 000 plants ha -1 . The assay included 480 plants and 1 row for each cultivar. Ten blueberry cultivars were evaluated: ‘Blue Ribbon’, ‘Duke’, ‘Camelia’, ‘Cargo’, ‘Last Call’, ‘Legacy’, ‘Ochlockonee’, ‘Suzie Blue’, ‘Ventura’, and ‘Victoria’. Plants were fertilized twice a week with macro- and micronutrient solutions (Table 2) supplemented with one of four different ammonium sulfate concentrations per treatment. Irrigation was conducted with a drip system from October to April. Ten irrigation lines were placed along the rows of plants to independently irrigate each variety. The treatments were applied at different flow rates with two emitters per plant (Supertif PCND, Rivulis, Kibbutz Gvat, Jezreel Valley, Israel): two emitters at 1.1 L h -1 (70%), one emitter at 1.1 and one at 2.2 L h -1 (100%), and two emitters at 2.2 L h -1 (130%). Plants were irrigated daily at a rate of 2 to 3 min every hour (irrigation events) until substrate saturation (onset of leaching) was reached using an irrigation controller (Pro-C support, Hunter, San Marcos, California, USA). The number of irrigation events per day and the duration of each event were adjusted once a week with a water balance to determine a 100% water replacement level. The water balance was calculated for each variety with four replicates of plants fertilized with 100% N, assuming that the 24 h mean weight loss of the container would be equal to the daily transpiration rate of the plant. Pots and pot plates containing the leachate were removed and weighed with an electronic balance at an accuracy of 2 to 5 g (0.03 to 0.07 mm) on two consecutive days at the same time. Pot changes were used to calculate the total water volumes to control the soil moisture content in the pots according to the following