BEREKENING VAN KOUE EENHEDE

1. BEREKENING VAN KOUE EENHEDE deur Linda De Wet

2. INLEIDING • Dormansie by plante 1. Endodormansie of rusperiode Plante sal nie groei nie -interne “restraints” Verkoelingsure (“Chilling hours”) 2. Ektodormansie Toestande (buite die plant) nie reg nie, gewoonlik te koud Dormante periode – na die rusperiode

3. INLEIDING • Verkoelingsure/Koue-eenheidsure benodig varieer tussen 700 en 1300 ure of meer • Indien warm weer voorkom alvorens die voltooing van rus, sal geen groei plaasvind nie • Bg laat die plant toe om die winter te herken en aanbreek van lente te bepaal • Verkoeling en rus verhoed plante om groei te inisieer tydens warm periodes in die middel van die winter • So ‘n geval sal toelaat dat bome hul bestandheid teen koue verloor, dws. As groei eers begin, dan kan die plant nie sy vermoe om koue te weerstaan verhoog nie, en kan so skade opdoen as dit baie koud word

4. INLEIDING • As die verkoelingsvereiste bereik word, het plante die rusperiode voltooi en is maar net dormant omdat die weer te koud is vir vinnige groei om plaas te vind • Verkoelingsvereistes word gewoonlik bereik teen middelwinter. Met die aanbreek van warmer weer sal die plante weer begin groei

5. KOUE EENHEDE • Verkoeling (Chilling) • Proses waarby die plant tyd meet gedurende die winter. Die plant stip die hoeveelheid tyd bokant0 oC (vriespunt) en onder 10 oC • Eintlik is temperature tussen 4 oC en 7 oC meer prakties • Verkoelingseenhede • Stimuleer groei • Ontwikkel blare/vrugte • Vrugteset

6. KOUE EENHEDE • Verkoelingseenhede varieer met spesie en ligging • Die geakumuleerde minimum temperatuur moet minder as die drumpelwaarde wees • Toepassings van verkoelingseenhede is om: • Die einde van die rusperiode te voorspel • Bepaling van kweekpraktyke • Indentifisering van potensiele groeigebiede • Probleme sluit in beskikbaarheid van uurlikse weerdata. Gewoonweg is slegs daaglikse Ta, Tmx and Tmn beskikbaar

7. KOUE EENHEDE • Verkoelingsperiodes = Vernalisasie = Termoperiodisme = “to make springlike” • Benodig in sekere plante vir blom om plaas te vind • Vind plaas tydens ‘n 2 - 6 week periode met ‘n temperatuur van < 10 oC • Hierdie waardes kan nul word indien Ta te hoog is, by 30 oC - 35 oC

8. BEREKENING VAN VERKOELINGS-/KOUE-EENHEDE • GebruikTmx en Tmn • Die metodeomuurlikse data temodeleer is as volg: • Gebruiksinuskurwesvanafsonsopkoms tot sonsondergang • Gebruik log in die nag wanneerafkoelingplaasvind • Tydenssonskyn: Tt = (Tmx-Tmn).sin[/(D+4)]+Tmn • In die nag: Tt = Tss - [(Tss-Tmn)/{ln(24-D)}]ln(t) Where Tt = temperatuur by tyd t nasonopkoms of tyd t nasonsondergang Tmx = maksimumtemperatuur Tmn = minimum temperatuur D = daglengte (ure) Tss = temperatuur by sonsondergang

9. BEREKENING VAN KOUE-EENHEDE Tabel 1 Gebruik Tt om koue-eenhede (KE) te bereken, wat in uur gemeet is (Utah model)

10. Tabel 2 KE vir vrugte

11. Verspreidingspatroon van geakkumuleerdepositiewekoueeenhedeoorSuidAfrikagedurende die winter vir 1950 – 1999 (waargenomeklimaat) (http://rava.qsens.net/themes/agriculture_template/school-of-bio-resources-engineering-and-environmental-hydrology-ukzn/ech_his_pcun_mean%20-map1.jpg/view

12. Tabel 3 Koue-eenhede vir plekname in SA

13. Tabel 4 Ontkiemingstemperature vir sade

14. SADE • Vir sade • Ontkieming van sade is laag by lae temperature. • Optimale Ta = hoogste ontkieming in die kortste tyd.

15. Tabel 5 Boonstelimietevir KE (Algemeen - vir SA)

16. Post categories: climate change,temperature VOORBEELD VAN KLIMAATSVERANDERING http://www.bbc.co.uk/blogs/gardening/2010/12/the-impact-of-climate-change.shtml • Jim McColl | 16:02 UK time, Thursday, 9 December 2010 • Global Warming? Huh! Let’s face a couple of incontrovertible facts: • We are an off-shore island. • We have therefore a maritime climate – a lack of extremes, plenty of moisture all year round but unpredictable because of the all-pervading influence of the sea • Some are sceptical about climate change but I think most people would sign up to the fact that something is happening. Until last winter (09/10) and the present one to date it was being argued that winters would be milder but wetter. Gardeners would be worse off because milder winters would lead to less winterkill of damaging organisms. Is this just a blip on last year's blip? • Evidence that winters are getting milder in some areas has been shown in a serious way, and affecting food production. Here is one example.

17. VOORBEELD VAN KLIMAATSVERANDERING A very high percentage of the blackcurrant varieties; now grown in Britain for commercial fruit production, were bred at the Scottish Crop Research Institute; they carry the ‘Ben’ prefix. To be technical, all temperate fruits – apples, pears, plums, soft fruit must experience a period of low temperature to complete their annual physiological life cycle. It is referred to as the ‘chilling requirement’ and will vary from one fruit species to another and indeed one cultivar to another. The use of the word ‘chilling’ may be slightly misleading. When I worked in this area of endeavour we called them units of ‘coolth’ (as opposed to warmth!) The plants collect these low temperature ‘units’ cumulatively, they ‘bank’ the low temp degrees, which must then add up to a given figure if the cycle is to be completed normally.. For example, in the dormant season, the blackcurrant variety Ben Lomond must collect 2000 hrs below 7.2 °C and if they don’t get them, problems will arise.  It has been recorded that commercial plantations of some of these varieties in the south of England have reported erratic bud break, leading to a reduction in fruit quality. This is one of the classic symptoms of not reaching the chill totals. In layman’s terms, the winters have been too mild .

18. GEVOLGTREKKINGS • Koue-eenhede is ‘n NB deel van baie gewasse, groente en plante en is noodsaaklik vir normale ontwikkeling • KOUE-EENHEDE is ‘n interessante onderwerp maar benodig meer navorsing alvorens dit tot die maksimum potensiaal benut kan word • Dus, is hierdie ‘n geleentheid vir interessante nagraadse navorsing!

19. BAIE DANKIE