Managing temperature in potatoes to improve quality

Page last updated: Wednesday, 13 December 2017 - 2:35pm

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Heat and water stress reduce the quality of potatoes in summer in Western Australia. Crop water use increases with higher temperature, resulting in rapid reduction of soil moisture, which in turn leads to increased soil temperature. This page explains how, with some advance planning, such problems can be reduced.

Optimum temperatures for handling tubers

Tuber temperatures between 12 and 18°C are considered best for harvesting and handling tubers. Tubers warmer than 18–20°C and under drought stress are susceptible to black spot bruising. The optimum day/night temperatures for potato growth are 25/12°C. Harvesting when tuber pulp temperature exceeds 18°C or soil temperature is greater than 20°C increases the risk of microbial rots, especially in damaged tubers.

Soil temperatures

Optimum soil temperature for harvest is 12–18°C. Harvest temperatures greater than 25°C or lower than 5°C can lead to bruising.

Soil temperature is primarily controlled by air temperature and solar radiation. The drier the soil, the closer the soil temperature will be to air temperature. High soil temperatures can be reduced by more frequent irrigation to provide evaporative cooling.

Tuber development declines as soil temperature rises above 20°C and practically stops above 30°C. The number of tubers per plant is higher at low soil temperatures while bigger but fewer tubers are set at higher temperatures.

Seasons with long periods of high temperatures increase the rate of vine senescence at the end of the season, exposing the soil to more sunlight and higher temperatures. Tables 1 and 2 show average soil temperatures for some of the main potato producing areas in WA.

Table 1 Daily average, minimum and maximum soil temperatures in the Perth and Myalup potato growing areas in Western Australia recorded at DAFWA weather stations

Perth Myalup
Month Mean Min Max Mean Min Max
Jan 32 24 42 32 25 39
Feb 32 24 41 30 24 37
Mar 28 22 37 26 21 32
Apr 22 18 29 21 17 25
May 16 13 21 16 13 20
Jun 14 11 18 13 10 16
Jul 13 10 17 12 9 16
Aug 14 11 19 13 10 18
Sep 17 13 23 15 12 20
Oct 21 15 28 20 16 26
Nov 26 20 34 25 19 32
Dec 30 23 39 29 23 37
Table 2 Daily average, minimum and maximum soil temperatures in the Busselton, Manjimup and Pemberton potato growing areas in Western Australia recorded at DAFWA weather stations
  Busselton Manjimup Pemberton
Month Mean Min Max Mean Min Max Mean Min Max
Jan 29 18 43 25 19 33 32 24 42
Feb 28 18 42 25 19 33 32 24 41
Mar 25 15 39 22 18 29 28 22 37
Apr 20 12 32 17 14 22 22 18 29
May 16 10 24 14 11 18 16 13 21
Jun 13 8 19 11 9 14 14 11 18
Jul 12 8 17 10 8 14 13 10 17
Aug 13 8 19 11 9 15 14 11 19
Sep 15 9 23 13 10 17 17 13 23
Oct 18 10 28 15 12 20 21 15 28
Nov 22 12 36 19 15 25 26 20 34
Dec 26 16 40 22 17 28 30 23 39

For Manjimup and Pemberton, the major ware production areas, the high minimum soil temperature in March which is close to 20°C is considered undesirable for potato handling due to increased risk of microbiological decay (Table 2). The soil temperature in March ranges from 18 to 29°C in Manjimup. This means a high risk of bruising and rots if tubers are harvested at this time.

The main harvesting months at Busselton will have reduced risk of rots and bruising as minimum soil temperatures are within the range of 10–15°C which is considered the best for handling and harvesting tubers (Table 2). However, maximum soil temperatures in the warmer months are above 20°C and harvesting during the hotter parts of the day could lead to increased black spot bruise damage and increased risk of rots during storage.

Soil temperatures at Myalup from May to September will cause low risk of rots and bruising (Table 1). However, maximum temperatures in November and December are above 20°C and harvesting during the hotter parts of the day could lead to increased black spot bruises and risk of rots during storage.

Soil temperatures in the Perth area show reduced risk of rots and bruising during September (Table 1). Risk may increase later in the year as soil temperatures rise.

Contact information

Rachelle Johnstone
+61 (0)8 9780 6158
Peter Dawson
+61 (0)8 9892 8461
Andrew Taylor
+61 (0)8 9780 6241

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Rachelle Johnstone

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