Growth and yield responses of apricot (cv. Moorpark) to soil-applied nitrogen

Abstract

The effect of soil-applied nitrogen on the growth and yield of 12-year-old apricot Prunus armeniaca cultivar Moorpark trees growing on an orthic Tenosol in the Riverland region of South Australia was studied over 3 years. The experiment was set up in a randomised complete block design with 6 annual rates of nitrogen (0, 250, 500, 750, 1000 and 1250 g/tree.year) applied in the form of ammonium nitrate. Application was split into 30% at budburst, 30% 6 weeks after budburst and 40% after harvest. Growth in trunk circumference was significantly greater at 750 and 1000 g/tree.year than at the other rates of nitrogen. In years 1 and 2, the weight of water shoot growth removed at pruning was significantly higher at nitrogen rates of 750–1250 g/tree.year than from trees that received no nitrogen. It is suggested that for Moorpark apricots growing on an orthic Tenosol, applying nitrogen at rates of 750 g/tree.year and above produces levels of water shoot growth that are undesirable for tree management. Nitrogen application resulted in darker and more vivid green leaves as measured with a Minolta Chroma Meter. Concentration of nitrogen in mid-shoot leaves was increased with increase in applied nitrogen. Fruit size was significantly increased by applied nitrogen in year 1, but fruit size was not significantly affected in years 2 and 3. Nitrogen application increased fruit set in the second and third year. Yield of fresh fruit was not significantly affected in the first year, but was in subsequent years with the maximum yield obtained at a rate of 1000 g/tree.year of nitrogen in both years. Yield of dried fruit followed similar trends to that of fresh fruit. Fruit maturation was delayed by 4 to 8 days by nitrogen application. After 3 years, applying nitrogen at 1250 g/tree.year the pH of soil in the top 15 cm was 4.7 compared with 6.7 where no nitrogen was applied.