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.

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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.

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Peter Dawson

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