CCC research update on the development of nitrogen fertiliser guidelines for blueberry growers
This article was compiled by Dr Sophie Parks, Melinda Simpson & Gaius Leong from the Clean Coastal Catchments Research team.
July 2024
Managing the application of fertiliser to efficiently meet the nutrient needs of a crop helps to keep nutrients on farm while avoiding the waste of fertilisers. Additionally, this practice reduces the risk of excess nutrients being exported off farm where they can affect the water quality of creeks and rivers and the wider marine estate.
The Clean Coastal Catchments (CCC) Research project has been investigating the nitrogen (N) needs of Southern Highbush blueberry grown as an evergreen crop. This article provides an update on the experiment being conducted at the Wollongbar Agricultural Institute (NSW Department of Primary Industries and Regional Development) in northern NSW, to assess the impact of various rates of nitrogen supplied by fertigation to blueberries grown in substrate.
Experimental outline in brief
Fertigation treatments:
Five rates of N (50% nitrate, 50% ammonium) supplied via drippers to pots in fertigation solution (14, 60, 80, 100, 120 mg /L), each made with the same concentration of total salts (electrical conductivity, EC 0.92 dS/m), and pH of 5.7 and adjusted according to the weather conditions.
Plants and materials:
Southern highbush (Vaccinium corymbosum ‘11-11’), planted in May 2021 into 28 litre pots containing a commercial blend of coir, peat moss and perlite.
Key data collected:
- Whole-plant dry weight and plant nitrogen concentration on 3 dates for all N rates (July 2022, January 2023, March 2023). Three plants per treatment.
- Fruit production for 3 N rates (40, 60, 100 mg/L) during the 2023 season.
Our findings to date
On average, whole plants (roots and shoots) contained 0.8 g of N in July 2022, 3 g in January 2023, and 5 g in March 2023.
From these results we calculated that 20 months after planting, in the summer months between January and March 2023, each plant was taking up 0.5 g of N per week from the supplied fertigation.
In general, the total dry weight (growth) of the plants and their N concentration was greater at the higher rates of N in fertigation, than at the lower rates. However, despite the total plant growth being greater at 100 mg N/L, compared with 40 mg N/L, the total fruit production when we first measured it in 2023, was similar in count and total fresh weight (an average of 1.4 kg per plant across 12 harvests from mid-June to late October 2023).
The exception was that the average fresh weight of berries was greater for the 100 mg N/L treatment (2.41 g), compared with the 40 mg N/L treatment (2.17 g). Unfortunately, we were unable to take measurements of fruit production from all the treatments in 2023, however we are expanding our data collection to all five treatments for the current season in 2024.
The preliminary results emerging from these data suggest that the fertigation rate of 120 mg N/L is excessive and could be reduced to 100 mg N/L without reducing plant growth. This conclusion is based on the finding that there was no difference in plant growth between these two treatments. While we do not have fruit production data for the 120 and 100 mg N/L treatments in 2023, we are collecting fruit harvest data in 2024 to see if the totals for these treatments differ.
Other information that we are investigating and will report on in 2025, includes the role of plant canopy area and fruit number on fruit size, the impact of pruning severity on plant demand for N, and the critical N concentrations in leaves associated with optimum growth for an establishing crop.
Through this experiment at Wollongbar and our on-farm trials at Bucca, Corindi, and Woolgoolga, we are gathering data on how N is taken up and lost from the growing system. This information will be used to develop new fertiliser N guidelines for blueberry as an establishing crop, to be released in late 2024.
Key messages:
- A blueberry plant in a substrate system approximately 1.5 years after planting, takes up about 1.5 g of N per week during summer.
- In this study, the fertigation rate of 120 mg N/L was excessive and could be reduced to 100 mg N/L without reducing plant growth.
- The effect of fertigation N and plant N on berry production will be investigated for the 2024 season.
This Clean Coastal Catchments Research project was funded by the NSW Government under the Marine Estate Management Strategy.
The ten-year Strategy was developed by the NSW Marine Estate Management Authority to coordinate the management of the marine estate.
This article was originally compiled for publication in the Winter 2024 edition of the Australian Berry Journal. It was republished on this CCC Insights page on 31 July 2024.
