Effects of nitrogen availability on root dynamics in 'Bing' on Gisela~R6 sweet cherry trees

摘要

Available nitrogen (N) is a main soil factor affecting root production and mortality, and therefore the amount of roots at any given time. However, the mechanism of this effect is poorly understood. A study was carried out in a 'Bing'/"Gisela~R6' sweet cherry orchard in central Chile to study the effect of N fertilization on root growth dynamic, distribution and root production and mortality. The study was conducted in a five-year-old orchard with a density of 889 trees ha1. Two N rates were applied(0 and 60 kg N ha ') in a completely randomized design, with three repetitions corresponding to a rhizotron. Root growth was quantified as white root length from September 2011 to March 2012 from photographs of the rhizotrons taken weekly. In addition, shoot length and fruit diameter were measured. Root production and mortality was calculated as the difference in root length between two sampling dates; these values were accumulated over time. In trees with no N application, a single root peak was observed between 63 and 91 days after full bloom (DAFB), coinciding with the maximum growth rate of shoots and with fruits in phase III. In trees with 60 kg N ha1, there were at least three root peaks at 56, 91 and 119 DAFB, and most of root growth occurred after cessation of shoot growth and harvest. Cumulative root production and mortality in the fertilized treatment was significantly greater than in control treatment, and root distribution along soil profile was more homogeneous. More than 80% of root production and mortality was concentrated below 50 cm depth in trees with no N fertilization. No significant differences due to N fertilization were observed in shoot length and fruit diameter. Our results indicate that N application led to a sustained rootproduction throughout the growing season.