EFFECTS OF FERTIGATION TIMING ON GROWTH AND DEVELOPMENT IN STRAWBERRY 'KORONA'

Abstract

Increased focus on targeted fertilization to improve specific processes in the plant has hypothesised that the common practice of spring fertilization could be substituted by other techniques. Two pot trials were set up to increase the knowledge on effects of fertilizer timing in small overwintered plants and runner plants potted in spring and fertigated with a complete nutrient solution until October. At defined developmental stages, the electric conductivity (EC) of the nutrient solution was increased with extra calcium nitrate for a period of three weeks, in addition to two treatments with continuously high or low EC. In Trial 2, compost used as substrate was also tested. Vegetative and generative traits were recorded during the trial and after destructive harvests. The results showed significant effects of fertigation timing, although there was a high degree of variation in the plant material. A high fertigation rate early in the growing season generally increased vegetative growth and runner development, while a high fertilizer rate applied in spring or autumn was positive for yield the following season. Plants grown in compost were phenotypically very different from the others. Fertigation in spring or autumn enhanced yield the following season, and based on this trial we cannot recommend to substitute spring fertilization with fertilization in other periods. INTRODUCTION Strawberry (Fragaria × ananassa) ‘Korona’ is a facultative short day (SD) plant where the axillary buds in the crown forms runners in long day (LD) conditions, while crown branching and flowers are initiated in SD (Konsin et al., 2001). The phenology of the strawberry plant implies that some of the plant traits could be enhanced by precision fertilization, stimulating specific developmental stages or plant organs. Timing of Nitrogen (N) application prior to or during the period of the flower differentiation significantly influence on the development of flowers and inflorescences (Sonsteby et al., 2009; Lieten, 2002), but effects of fertigation at specific periods during the growing season is not well documented. The great variation in yield responses in fertilizer trials in strawberry (see Strik et al., 2004 with references therein) requires a consideration of other factors than applied fertilizer rates in order to improve fertilizer strategies. Although seasonal growth pattern in June-bearing strawberry is mainly controlled by an interaction of temperature and photoperiod (Heide, 1977; Konsin et al., 2001), it is also influenced by internal competing sinks (Archbold and MacKown, 1995, 1997; Fernandez et al., 2001) and responses to growth limiting or stimulating factors such as water stress (Grant et al., 2010) and plant nutrient availability (e.g., Breen and Martin, 1981; Strik et al., 2004). The aim of the following trials was to describe vegetative and generative growth and development in ‘Korona’ during the season, and elucidate how plants and plant organs respond to increasing nutrient supply at defined developmental stages. The final objectives are to define optimal fertigation timing, as well as periods when nutrient access could or should be limited in order to improve fertilizer efficiency and yields. Proc. VIIth IS on Mineral Nutrition of Fruit Crops Eds.: S. Poovarodom and S. Yingjajaval Acta Hort. 984, ISHS 2013 144 MATERIALS AND METHODS Experiment 1 Small overwintered plug plants of ‘Korona’ from a certified commercial plant producer were potted in 3.5 L pots in a peat based potting compost in late April 2010, using 2 plants pot-1. The pots were placed on table tops in a polyethylene high tunnel and fertigated with a complete nutrient solution with EC 0.5 mS cm-1 from May 3. In defined periods of 3 weeks during the season, EC was increased with calcium nitrate to 2.2 mS cm-1: 1) Early spring (May 3-23), 2) Flowering (May 31-Jun 16), 3) Berry ripening (Jun 24-Jul 15), 4) Crown branching (Aug 2-22), 5) Flower differentiation (Aug 30-Sep 19). In addition, other plants were kept 6) Continuously with low EC (-), or 7) Continuously with high EC (Apr 30-Sep 30). Yield and berry size were recorded three times per week during the harvest season. Two to four days after termination of the increased EC periods (May 26, June 23, July 19, August 25 and September 22), four plants from all treatments were destructively harvested and separated into leaves, petioles, crowns and roots. The number of crowns and leaves was recorded, and leaf area was measured using a LI-COR area meter. The plant parts were dried at 70oC for dry weight (DW) measurements. The remaining 6 x 3 plants treatment-1 were kept outside for cold hardening under natural temperature conditions until December 1, when they were cold-stored at -2oC over the winter. From June 10 the following spring, 6 x 3 plants treatment-1were forced in a high poly-tunnel and grown for yield recordings. All plants were then supplied with a complete nutrient solution of EC 0.5 mS cm-1. Experiment 2 Fresh runner plants of ‘Korona’ from a certified commercial plant producer were potted in 1.5 L pots in a peat based potting compost on May 25, 2010 in a heated greenhouse, using 1 plant pot-1. In addition, a group of plantlets was potted in a commercial peat mix with cow dung compost (2:1) (Simontorp). The plantlets had two developed leaves when the trial was initiated, and were placed in a propagation tent until rooted. On June 10, when the plants had developed three leaves ±1, they were moved to table tops in an open, high polyethylene tunnel. There were 15 plants per treatment; growth recordings were made on 5 single plants while the remaining 10 plants are kept for yield control. The plants were fertigated with a complete nutrient solution with EC 0.4 mS cm-1 from May 27 until October 3, except in defined periods when fertigation was increased to 2.0 by calcium nitrate: 1) EC 2 three weeks from start (May 27-June 17), 2) EC 2 prior to crown branching (July 11-29), 3) EC 2 during crown branching (August 8-26), 4) EC 2 during flower differentiation (September 5-26). In addition two other treatments were present: 5) EC 2 continuously (May 27-Oct 3) or 6) EC 0.4 continuously. Every two weeks, leaves and crowns on five plants per treatment were counted, and runners were counted and removed. Runners from each treatment were dried and weighed for calculation of total dry matter accumulation at the end of the season. On October 3-5, five plants treatment-1 were destructively harvested and separated into leaves, petioles, crown and root, and dried at 70oC for DW measurements. Plants were kept outside for hardening under natural temperature conditions. They were coldstored from November 29 at -2oC, and were forced on table tops with standard fertigation from June 2012 for yield and growth registrations. Because of a technical error in the fertigation system, vegetative recordings on the plants supplied with a high fertigation rate in spring were excluded, but the plants fertigated according to the plan were kept for yield control in 2012. The experimental data were subjected to analysis of variance (ANOVA) by standard procedure using MiniTab® Statistical Software programme package.

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