Precision nitrogen fertigation and irrigation management for improved apple quality

Nitrogen (N) management is a balance to meet tree demands for current seasons’ crop as well as for internal storage for the subsequent season whilst reducing N loss via runoff and deep drainage. Whilst fertigation is commonly practised by apple growers in Australia, research into tree nutrient requirements and therefore fertigation management strategies are limited. In the Huon valley of southern Tasmania, we applied N (Ca(NO₃)₂) treatments pre- and post-harvest combined with high (4 L/hr), medium (2.3 L/hr) and low (1.6 L/hr) irrigation treatments to 10 year-old ‘Galaxy’ trees grafted on M26 rootstocks. We measured yield, fruit quality attributes and fruit N content. Data from the second season revealed fruit in the low irrigation treatments were significantly smaller (152 g) but firmer, with higher total soluble solids (11.80 Brix). Irrigation treatment had no effect on fruit colour, however fruit background colour decreased significantly with increased current season N application. Fruit N content was not significantly influenced by N application. This study demonstrates the strong linkage between N and irrigation management on the above ground components of orchard production and urges caution for growers implementing pre-harvest fertigation.