TEMPERATURE AND PLANT GROWTH

1. TEMPERATURE AND PLANT GROWTH

2. What is Temperature? • Temperature is the measurement of how hot something is. • In NZ we measure temperature in degrees Celsius (oC). • The minimum temperature is how low the temperature will go, whereas the maximum is the highest it will go. • Temperature fluctuates throughout the day, and throughout the year. • The temperature has effects on plants. • Plants need certain temperatures in which to flourish. • All plants have an optimum temperature at which they function best.

3. Student Activities Read pg 20 and highlight the key ideas.

4. Key Ideas • NZ has a temperate climate • NZ does not have a large temp. range. • January and February are the warmest months, July is the coldest. • The highest summer temps. Are usually recorded on the east coast of the South Island. • The far north has more subtropical weather. • Temp. increases as altitude decreases and air temp. can be changed by features such as slopes and wind currents around mountain ranges.

5. Air Temperature Read through page 21 and answer the questions. Read page 311 – 332 in Dynamic Ag.

6. Answers 2. Hawkes Bay 3. Central Otago 4. Central Otago Read page 23 in workbook Use the following slides to fill in the effects of temp. on plants.

10. Growing Degree Days • Temperature on its own has been found not to be a reliable indicator of an area’s suitability for growing a particular crop. • Growing degree days, however, have been found to be a better indicator. • Researchers have found that plants need a certain amount of heat to survive. • This is known as the base (minimum) temperature or threshold temperature for that particular plant. For maize this is 10o.

11. In the absence of extreme conditions such as unseasonal drought or disease, plants grow in a cumulative stepwise manner which is strongly influenced by the ambient temperature. • Growing degree days take aspects of local weather into account and allow gardeners to predict (or, in greenhouses, even to control) the plants’ pace toward maturity. • Unless stressed by other environmental factors like moisture, the development rate from emergence to maturity for many plants depends upon the daily air temperature. • Because many developmental events of plants and insects depend on the accumulation of specific quantities of heat, it is possible to predict when these events should occur during a growing season regardless of differences in temperatures from year to year. • Growing degrees (GDs) is defined as the number of temperature degrees above a certain threshold base temperature, which varies among crop species. • The base temperature is that temperature below which plant growth is zero. • GDs are calculated each day as maximum temperature plus the minimum temperature divided by 2 (or the mean temperature), minus the base temperature. • GDUs are accumulated by adding each day’s GDs contribution as the season progresses.

12. GDUs can be used to: assess the suitability of a region for production of a particular crop; estimate the growth-stages of crops, weeds or even life stages of insects; predict maturity and cutting dates of forage crops; predict best timing of fertilizer or pesticide application; estimate the heat stress on crops; plan spacing of planting dates to produce separate harvest dates.

13. BarleyHordeum vulgare125-162 GDD to emergence and 1290-1540 GDD to maturity • Wheat (Hard Red)Triticum aestivum143-178 GDD to emergence and 1550-1680 GDD to maturity • OatsAvena sativa1500-1750 GDD to maturity • Corn (maize)Zea mays2700 GDD to crop maturity

14. Base temperature for some crops and pasture plants.

15. Growing-Degree-Days (4°C base temperature) for long-term weather stations in New Zealand.

16. Note: anomalies can occur when you have a cloudy day at say 15°C and then the sun comes out for 15 minutes. • The temperature climbs by 8 - 10°C, causing a sudden spike on the graph giving a not so accurate picture of GDDs for that particular day. • The most accurate method, costing about $300 per unit, is to install a data logger that takes automatic temperature readings every 30 minutes and can store up to 6 months data. This will smooth out any variations. • The growing degree days required to produce quality cherries is 800+. • As a comparison, apples require a minimum of 700 GDDs, with grapes and olives needing 900+ GDDs. • Ideal growing temperatures for cherries are between 10°C – 30°C, with temperatures above and below this range limiting growth.

17. Read through pg 24 • Attempt the questions on GDD

18. Answers • The number of days that the plant is able to grow • Growing degree days take into consideration seasonal variations whereas calendar do not. • The plant does not grow below that temperature. • Central Otago – 966 and Hawkes Bay 1642

19. 5. Hawkes Bay 6. In a year where there is low sunshine there may not be enough growing degree days for the crop to mature and ripen. 7. Tauranga has 1365 growing degree days. So using the 1300GDD column and the 20th of September column they intercept on the 8th of February. 8. It is just coming out of spring and the days are still low in temp, therefore there are not many days in September above 10o C, so it takes longer to reach the required growing degree days.

20. Sweet corn are frost tender, so planting later will reduce the risk of frost. Sweetcorn also requires a soil temperature of 12oC, so by planting a month later increases the soil temperature. Planting a month later means harvest is only 3 days later. • Nelson has 1090 growing degree days. So using the 1000GDD coloumn, the earliest he can 0plant his peas is the 1st of September.

21. SOIL TEMPERATURE Air temp – the cooler… Aspect – soils on slopes… Climate – Drier climates… Season- in the summer Soil Colour – soils that are dark… Soil depth – soils that are deep… Soil texture – soils such as sandy … Vegetation cover – soils that are covered in… Water availability- soils that are wet…

22. Frosts Read pg 29 in your workbooks Fill in the gaps

23. Frost answers • What are frosts? – still, radiation, wind, southerly • Frost behaviour – warm, shelterbelts, altitude • Measuring frosts – air, ground • Negative effects of frosts – water, higher, cell, plant, nutrients, frost, flowers, leaves, crop, fruit • Positive effects – pests, chilling

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