Blackcurrants require winter chilling and the North Island cannot provide this. There are a few small growers in the North Island but no commercial properties that I am aware of. All commercial growers are in the South Island with the majority in the Canterbury region and Nelson area.
I beleive winter chilling and soil moisture are major contributing factors on tonnage. I am now recording data for these factors on my own farm and set out below is information on the instruments and results of my findings so far.
I have two dataloggers recording air temperatures. One is a Hobo H8 pro 2-channel logger recording air temperature and relative humidity. The second is a Hobo H8 4-channel external logger recording air temperature, soil temperature and two soil moisture meters. I have been recording data from my own farm since October 1999 and purchased air temperatures recorded for the past five years at the local airport two kilometres away. The airport temperatures would be slightly colder than my farm, but I did not allow for this in my calculations. With advice from the blackcurrants research team I decided to use the data for the four month period 1st May to 31st August for winter chilling. They also supplied a formula to work out the winter chilling hours. When I graphed the past five year air temperature data in conjunction with the tonnages for those years I found a definite link between the two. Over the next few years this information may help with farm management.
I have two Aquaflex Soil Moisture meters connected to the Hobo logger. The Aquaflex are 3 metres long and are at a depth of 150mm and 270mm. I also have a Hydro-Sense hand held meter with 200mm probes. This displays data in Volumetric Water Volume. Soil Moisture is a new topic for me as I have always beleived that the region I farm in has not required irrigation. I am the only farm in the area with irrigation. Since I have been recording soil moisture I have been amazed at the volume of water blackcurrants require. In the past when I have had a good rainfall I had thought soil moisture would have been adequate for three to four weeks, but now find it only lasts for ten days and I should be irrigating. I have 11.5 hectares of overhead sprinklers installed for frost protection but find this being used mainly for irrigation now. I also purchased a small traveling irrigator in the spring of 1999 and found this well worth while. I do not plan to purchase any more irrigation equipment until I get more data to support the expense.
For more information on the equipment used as above, go to my links page.